text: /**@file mpc.c 
   * @brief See the header for licensing, and https://github.com/orangeduck/mpc for
   * the original source, this file has been taken from commit 
   * "37c12b1d43605c2b897b4bacd6d45c450920aea4" and subsequently modified */
  
  #include "mpc.h"
  #include <assert.h>
  
  static const char *emsg(void)
  {
    return errno ? strerror(errno) : "unknown reason";
  }
  
  static void fatal(const char *fmt, ...)
  {
    va_list args;
    assert(fmt);
    va_start(args, fmt);
    vfprintf(stderr, fmt, args);
    va_end(args);
    fputc('\n', stderr);
    exit(EXIT_FAILURE);
  }
  
  static void *allocate(size_t sz)
  {
    errno = 0;
    void *r = calloc(sz, 1);
    if(!r)
      fatal("allocated failed: %s", emsg());
    return r;
  }
  
  static void *reallocate(void *p, size_t n)
  {
    /**@bug something is not allocating enough memory, the +1 fixes the Valgrind issues*/
    errno = 0;
    void *r = realloc(p, n+1); 
    if(!r)
      fatal("reallocate failed: %s", emsg());
    return r;
  }
  
  /*
  ** State Type
  */
  
  static mpc_state_t mpc_state_invalid(void) {
    mpc_state_t s;
    s.pos = -1;
    s.row = -1;
    s.col = -1;
    return s;
  }
  
  static mpc_state_t mpc_state_new(void) {
    mpc_state_t s;
    s.pos = 0;
    s.row = 0;
    s.col = 0;
    return s;
  }
  
  /*
  ** Input Type
  */
  
  /*
  ** In mpc the input type has three modes of 
  ** operation: String, File and Pipe.
  **
  ** String is easy. The whole contents are 
  ** loaded into a buffer and scanned through.
  ** The cursor can jump around at will making 
  ** backtracking easy.
  **
  ** The second is a File which is also somewhat
  ** easy. The contents are never loaded into 
  ** memory but backtracking can still be achieved
  ** by seeking in the file at different positions.
  **
  ** The final mode is Pipe. This is the difficult
  ** one. As we assume pipes cannot be seeked - and 
  ** only support a single character lookahead at 
  ** any point, when the input is marked for a 
  ** potential backtracking we start buffering any 
  ** input.
  **
  ** This means that if we are requested to seek
  ** back we can simply start reading from the
  ** buffer instead of the input.
  **
  ** Of course using `mpc_predictive` will disable
  ** backtracking and make LL(1) grammars easy
  ** to parse for all input methods.
  **
  */
  
  enum {
    MPC_INPUT_STRING = 0,
    MPC_INPUT_FILE   = 1,
    MPC_INPUT_PIPE   = 2
  };
  
  enum {
    MPC_INPUT_MARKS_MIN = 32
  };
  
  enum {
    MPC_INPUT_MEM_NUM = 512
  };
  
  typedef struct {
    char mem[64];
  } mpc_mem_t;
  
  typedef struct {
  
    int type;
    char *filename;  
    mpc_state_t state;
    
    char *string;
    char *buffer;
    FILE *file;
    
    int suppress;
    int backtrack;
    int marks_slots;
    int marks_num;
    mpc_state_t *marks;
    
    char *lasts;
    char last;
    
    size_t mem_index;
    char mem_full[MPC_INPUT_MEM_NUM];
    mpc_mem_t mem[MPC_INPUT_MEM_NUM];
    
  } mpc_input_t;
  
  static mpc_input_t *mpc_input_new_string(const char *filename, const char *string) {
  
    mpc_input_t *i = allocate(sizeof(mpc_input_t));
    
    i->filename = allocate(strlen(filename) + 1);
    strcpy(i->filename, filename);
    i->type = MPC_INPUT_STRING;
    
    i->state = mpc_state_new();
    
    i->string = allocate(strlen(string) + 1);
    strcpy(i->string, string);
    i->buffer = NULL;
    i->file = NULL;
    
    i->suppress = 0;
    i->backtrack = 1;
    i->marks_num = 0;
    i->marks_slots = MPC_INPUT_MARKS_MIN;
    i->marks = allocate(sizeof(mpc_state_t) * i->marks_slots);
    i->lasts = allocate(sizeof(char) * i->marks_slots);
    i->last = '\0';
    
    i->mem_index = 0;
    memset(i->mem_full, 0, sizeof(char) * MPC_INPUT_MEM_NUM);
    
    return i;
  }
  
  static mpc_input_t *mpc_input_new_nstring(const char *filename, const char *string, size_t length) {
  
    mpc_input_t *i = allocate(sizeof(mpc_input_t));
    
    i->filename = allocate(strlen(filename) + 1);
    strcpy(i->filename, filename);
    i->type = MPC_INPUT_STRING;
    
    i->state = mpc_state_new();
    
    i->string = allocate(length + 1);
    strncpy(i->string, string, length);
    i->string[length] = '\0';
    i->buffer = NULL;
    i->file = NULL;
    
    i->suppress = 0;
    i->backtrack = 1;
    i->marks_num = 0;
    i->marks_slots = MPC_INPUT_MARKS_MIN;
    i->marks = allocate(sizeof(mpc_state_t) * i->marks_slots);
    i->lasts = allocate(sizeof(char) * i->marks_slots);
    i->last = '\0';
    
    i->mem_index = 0;
    memset(i->mem_full, 0, sizeof(char) * MPC_INPUT_MEM_NUM);
    
    return i;
  
  }
  
  static mpc_input_t *mpc_input_new_pipe(const char *filename, FILE *pipe) {
  
    mpc_input_t *i = allocate(sizeof(mpc_input_t));
    
    i->filename = allocate(strlen(filename) + 1);
    strcpy(i->filename, filename);
    
    i->type = MPC_INPUT_PIPE;
    i->state = mpc_state_new();
    
    i->string = NULL;
    i->buffer = NULL;
    i->file = pipe;
    
    i->suppress = 0;
    i->backtrack = 1;
    i->marks_num = 0;
    i->marks_slots = MPC_INPUT_MARKS_MIN;
    i->marks = allocate(sizeof(mpc_state_t) * i->marks_slots);
    i->lasts = allocate(sizeof(char) * i->marks_slots);
    i->last = '\0';
    
    i->mem_index = 0;
    memset(i->mem_full, 0, sizeof(char) * MPC_INPUT_MEM_NUM);
    
    return i;
    
  }
  
  static mpc_input_t *mpc_input_new_file(const char *filename, FILE *file) {
    
    mpc_input_t *i = allocate(sizeof(mpc_input_t));
    
    i->filename = allocate(strlen(filename) + 1);
    strcpy(i->filename, filename);
    i->type = MPC_INPUT_FILE;
    i->state = mpc_state_new();
    
    i->string = NULL;
    i->buffer = NULL;
    i->file = file;
    
    i->suppress = 0;
    i->backtrack = 1;
    i->marks_num = 0;
    i->marks_slots = MPC_INPUT_MARKS_MIN;
    i->marks = allocate(sizeof(mpc_state_t) * i->marks_slots);
    i->lasts = allocate(sizeof(char) * i->marks_slots);
    i->last = '\0';
    
    i->mem_index = 0;
    memset(i->mem_full, 0, sizeof(char) * MPC_INPUT_MEM_NUM);
    
    return i;
  }
  
  static void mpc_input_delete(mpc_input_t *i) {
    
    free(i->filename);
    
    if (i->type == MPC_INPUT_STRING) { free(i->string); }
    if (i->type == MPC_INPUT_PIPE) { free(i->buffer); }
    
    free(i->marks);
    free(i->lasts);
    free(i);
  }
  
  static int mpc_mem_ptr(mpc_input_t *i, void *p) {
    return
      (char*)p >= (char*)(i->mem) &&
      (char*)p <  (char*)(i->mem) + (MPC_INPUT_MEM_NUM * sizeof(mpc_mem_t));
  }
  
  static void *mpc_allocate(mpc_input_t *i, size_t n) {
    size_t j;
    char *p;
    
    if (n > sizeof(mpc_mem_t)) { return allocate(n); }
    
    j = i->mem_index;
    do {
      if (!i->mem_full[i->mem_index]) {
        p = (void*)(i->mem + i->mem_index);
        i->mem_full[i->mem_index] = 1;
        i->mem_index = (i->mem_index+1) % MPC_INPUT_MEM_NUM;
        return p;
      }
      i->mem_index = (i->mem_index+1) % MPC_INPUT_MEM_NUM;
    } while (j != i->mem_index);
    
    return allocate(n);
  }
  
  static void *mpc_calloc(mpc_input_t *i, size_t n, size_t m) {
    char *x = mpc_allocate(i, n * m);
    memset(x, 0, n * m);
    return x;
  }
  
  static void mpc_free(mpc_input_t *i, void *p) {
    size_t j;
    if (!mpc_mem_ptr(i, p)) { free(p); return; }
    j = ((size_t)(((char*)p) - ((char*)i->mem))) / sizeof(mpc_mem_t);
    i->mem_full[j] = 0;
  }
  
  static void *mpc_reallocate(mpc_input_t *i, void *p, size_t n) {
    
    char *q = NULL;
    
    if (!mpc_mem_ptr(i, p)) { return reallocate(p, n); }
    
    if (n > sizeof(mpc_mem_t)) {
      q = allocate(n);
      memcpy(q, p, sizeof(mpc_mem_t));
      mpc_free(i, p);
      return q;
    }
    
    return p;
  }
  
  static void *mpc_export(mpc_input_t *i, void *p) {
    char *q = NULL;
    if (!mpc_mem_ptr(i, p)) { return p; }
    q = allocate(sizeof(mpc_mem_t));
    memcpy(q, p, sizeof(mpc_mem_t));
    mpc_free(i, p);
    return q; 
  }
  
  static void mpc_input_backtrack_disable(mpc_input_t *i) { i->backtrack--; }
  static void mpc_input_backtrack_enable(mpc_input_t *i) { i->backtrack++; }
  
  static void mpc_input_suppress_disable(mpc_input_t *i) { i->suppress--; }
  static void mpc_input_suppress_enable(mpc_input_t *i) { i->suppress++; }
  
  static void mpc_input_mark(mpc_input_t *i) {
    
    if (i->backtrack < 1) { return; }
    
    i->marks_num++;
    
    if (i->marks_num > i->marks_slots) {
      i->marks_slots = i->marks_num + i->marks_num / 2;
      i->marks = reallocate(i->marks, sizeof(mpc_state_t) * i->marks_slots);
      i->lasts = reallocate(i->lasts, sizeof(char) * i->marks_slots);
    }
  
    i->marks[i->marks_num-1] = i->state;
    i->lasts[i->marks_num-1] = i->last;
    
    if (i->type == MPC_INPUT_PIPE && i->marks_num == 1) {
      i->buffer = calloc(1, 1);
    }
    
  }
  
  static void mpc_input_unmark(mpc_input_t *i) {
    
    if (i->backtrack < 1) { return; }
    
    i->marks_num--;
    
    if (i->marks_slots > i->marks_num + i->marks_num / 2
    &&  i->marks_slots > MPC_INPUT_MARKS_MIN) {
      i->marks_slots = 
        i->marks_num > MPC_INPUT_MARKS_MIN ?
        i->marks_num : MPC_INPUT_MARKS_MIN;
      i->marks = reallocate(i->marks, sizeof(mpc_state_t) * i->marks_slots);
      i->lasts = reallocate(i->lasts, sizeof(char) * i->marks_slots);      
    }
    
    if (i->type == MPC_INPUT_PIPE && i->marks_num == 0) {
      free(i->buffer);
      i->buffer = NULL;
    }
    
  }
  
  static void mpc_input_rewind(mpc_input_t *i) {
    
    if (i->backtrack < 1) { return; }
    
    i->state = i->marks[i->marks_num-1];
    i->last  = i->lasts[i->marks_num-1];
    
    if (i->type == MPC_INPUT_FILE) {
      fseek(i->file, i->state.pos, SEEK_SET);
    }
    
    mpc_input_unmark(i);
  }
  
  static int mpc_input_buffer_in_range(mpc_input_t *i) {
    return i->state.pos < (long)(strlen(i->buffer) + i->marks[0].pos);
  }
  
  static char mpc_input_buffer_get(mpc_input_t *i) {
    return i->buffer[i->state.pos - i->marks[0].pos];
  }
  
  static int mpc_input_terminated(mpc_input_t *i) {
    if (i->type == MPC_INPUT_STRING && i->state.pos == (long)strlen(i->string)) { return 1; }
    if (i->type == MPC_INPUT_FILE && feof(i->file)) { return 1; }
    if (i->type == MPC_INPUT_PIPE && feof(i->file)) { return 1; }
    return 0;
  }
  
  static char mpc_input_getc(mpc_input_t *i) {
    
    char c = '\0';
    
    switch (i->type) {
      
      case MPC_INPUT_STRING: return i->string[i->state.pos];
      case MPC_INPUT_FILE: c = fgetc(i->file); return c;
      case MPC_INPUT_PIPE:
      
        if (!i->buffer) { c = getc(i->file); return c; }
        
        if (i->buffer && mpc_input_buffer_in_range(i)) {
          c = mpc_input_buffer_get(i);
          return c;
        } else {
          c = getc(i->file);
          return c;
        }
      
      default: return c;
    }
  }
  
  static char mpc_input_peekc(mpc_input_t *i) {
    
    char c = '\0';
    
    switch (i->type) {
      case MPC_INPUT_STRING: return i->string[i->state.pos];
      case MPC_INPUT_FILE: 
        
        c = fgetc(i->file);
        if (feof(i->file)) { return '\0'; }
        
        fseek(i->file, -1, SEEK_CUR);
        return c;
      
      case MPC_INPUT_PIPE:
        
        if (!i->buffer) {
          c = getc(i->file);
          if (feof(i->file)) { return '\0'; }
          ungetc(c, i->file);
          return c;
        }
        
        if (i->buffer && mpc_input_buffer_in_range(i)) {
          return mpc_input_buffer_get(i);
        } else {
          c = getc(i->file);
          if (feof(i->file)) { return '\0'; }
          ungetc(c, i->file);
          return c;
        }
      
      default: return c;
    }
    
  }
  
  static int mpc_input_failure(mpc_input_t *i, char c) {
  
    switch (i->type) {
      case MPC_INPUT_STRING: { break; }
      case MPC_INPUT_FILE: fseek(i->file, -1, SEEK_CUR); { break; }
      case MPC_INPUT_PIPE: {
        
        if (!i->buffer) { ungetc(c, i->file); break; }
        
        if (i->buffer && mpc_input_buffer_in_range(i)) {
          break;
        } else {
          ungetc(c, i->file); 
        }
      }
      default: { break; }
    }
    return 0;
  }
  
  static int mpc_input_success(mpc_input_t *i, char c, char **o) {
    
    if (i->type == MPC_INPUT_PIPE
    &&  i->buffer && !mpc_input_buffer_in_range(i)) {
      i->buffer = reallocate(i->buffer, strlen(i->buffer) + 2);
      i->buffer[strlen(i->buffer) + 1] = '\0';
      i->buffer[strlen(i->buffer) + 0] = c;
    }
    
    i->last = c;
    i->state.pos++;
    i->state.col++;
    
    if (c == '\n') {
      i->state.col = 0;
      i->state.row++;
    }
    
    if (o) {
      (*o) = mpc_allocate(i, 2);
      (*o)[0] = c;
      (*o)[1] = '\0';
    }
    
    return 1;
  }
  
  static int mpc_input_any(mpc_input_t *i, char **o) {
    char x = mpc_input_getc(i);
    if (mpc_input_terminated(i)) { return 0; }
    return mpc_input_success(i, x, o);
  }
  
  static int mpc_input_char(mpc_input_t *i, char c, char **o) {
    char x = mpc_input_getc(i);
    if (mpc_input_terminated(i)) { return 0; }
    return x == c ? mpc_input_success(i, x, o) : mpc_input_failure(i, x);
  }
  
  static int mpc_input_range(mpc_input_t *i, char c, char d, char **o) {
    char x = mpc_input_getc(i);
    if (mpc_input_terminated(i)) { return 0; }
    return x >= c && x <= d ? mpc_input_success(i, x, o) : mpc_input_failure(i, x);  
  }
  
  static int mpc_input_oneof(mpc_input_t *i, const char *c, char **o) {
    char x = mpc_input_getc(i);
    if (mpc_input_terminated(i)) { return 0; }
    return strchr(c, x) != 0 ? mpc_input_success(i, x, o) : mpc_input_failure(i, x);  
  }
  
  static int mpc_input_noneof(mpc_input_t *i, const char *c, char **o) {
    char x = mpc_input_getc(i);
    if (mpc_input_terminated(i)) { return 0; }
    return strchr(c, x) == 0 ? mpc_input_success(i, x, o) : mpc_input_failure(i, x);  
  }
  
  static int mpc_input_satisfy(mpc_input_t *i, int(*cond)(char), char **o) {
    char x = mpc_input_getc(i);
    if (mpc_input_terminated(i)) { return 0; }
    return cond(x) ? mpc_input_success(i, x, o) : mpc_input_failure(i, x);  
  }
  
  static int mpc_input_string(mpc_input_t *i, const char *c, char **o) {
    
    const char *x = c;
  
    mpc_input_mark(i);
    while (*x) {
      if (!mpc_input_char(i, *x, NULL)) {
        mpc_input_rewind(i);
        return 0;
      }
      x++;
    }
    mpc_input_unmark(i);
    
    *o = mpc_allocate(i, strlen(c) + 1);
    strcpy(*o, c);
    return 1;
  }
  
  static int mpc_input_anchor(mpc_input_t* i, int(*f)(char,char), char **o) {
    *o = NULL;
    return f(i->last, mpc_input_peekc(i));
  }
  
  static mpc_state_t *mpc_input_state_copy(mpc_input_t *i) {
    mpc_state_t *r = mpc_allocate(i, sizeof(mpc_state_t));
    memcpy(r, &i->state, sizeof(mpc_state_t));
    return r;
  }
  
  /*
  ** Error Type
  */
  
  void mpc_err_delete(mpc_err_t *x) {
    int i;
    for (i = 0; i < x->expected_num; i++) { free(x->expected[i]); }
    free(x->expected);
    free(x->filename);
    free(x->failure);
    free(x);
  }
  
  void mpc_err_print(mpc_err_t *x) {
    mpc_err_print_to(x, stdout);
  }
  
  void mpc_err_print_to(mpc_err_t *x, FILE *f) {
    char *str = mpc_err_string(x);
    fprintf(f, "%s", str);
    free(str);
  }
  
  static void mpc_err_string_cat(char *buffer, int *pos, int *max, char const *fmt, ...) {
    /* TODO: Error Checking on Length */
    int left = ((*max) - (*pos));
    va_list va;
    va_start(va, fmt);
    if (left < 0) { left = 0;}
    (*pos) += vsprintf(buffer + (*pos), fmt, va);
    va_end(va);
  }
  
  static char char_unescape_buffer[4];
  
  static const char *mpc_err_char_unescape(char c) {
    
    char_unescape_buffer[0] = '\'';
    char_unescape_buffer[1] = ' ';
    char_unescape_buffer[2] = '\'';
    char_unescape_buffer[3] = '\0';
    
    switch (c) {
      case '\a': return "bell";
      case '\b': return "backspace";
      case '\f': return "formfeed";
      case '\r': return "carriage return";
      case '\v': return "vertical tab";
      case '\0': return "end of input";
      case '\n': return "newline";
      case '\t': return "tab";
      case ' ' : return "space";
      default:
        char_unescape_buffer[1] = c;
        return char_unescape_buffer;
    }
    
  }
  
  char *mpc_err_string(mpc_err_t *x) {
  
    int i;  
    int pos = 0; 
    int max = 1023;
    char *buffer = calloc(1, 1024);
    
    if (x->failure) {
      mpc_err_string_cat(buffer, &pos, &max,
      "%s: error: %s\n", x->filename, x->failure);
      return buffer;
    }
    
    mpc_err_string_cat(buffer, &pos, &max, 
      "%s:%i:%i: error: expected ", x->filename, x->state.row+1, x->state.col+1);
    
    if (x->expected_num == 0) { mpc_err_string_cat(buffer, &pos, &max, "ERROR: NOTHING EXPECTED"); }
    if (x->expected_num == 1) { mpc_err_string_cat(buffer, &pos, &max, "%s", x->expected[0]); }
    if (x->expected_num >= 2) {
    
      for (i = 0; i < x->expected_num-2; i++) {
        mpc_err_string_cat(buffer, &pos, &max, "%s, ", x->expected[i]);
      } 
      
      mpc_err_string_cat(buffer, &pos, &max, "%s or %s", 
        x->expected[x->expected_num-2], 
        x->expected[x->expected_num-1]);
    }
    
    mpc_err_string_cat(buffer, &pos, &max, " at ");
    mpc_err_string_cat(buffer, &pos, &max, mpc_err_char_unescape(x->recieved));
    mpc_err_string_cat(buffer, &pos, &max, "\n");
    
    return reallocate(buffer, strlen(buffer) + 1);
  }
  
  static mpc_err_t *mpc_err_new(mpc_input_t *i, const char *expected) {
    mpc_err_t *x;
    if (i->suppress) { return NULL; }
    x = mpc_allocate(i, sizeof(mpc_err_t));
    x->filename = mpc_allocate(i, strlen(i->filename) + 1);
    strcpy(x->filename, i->filename);
    x->state = i->state;
    x->expected_num = 1;
    x->expected = mpc_allocate(i, sizeof(char*));
    x->expected[0] = mpc_allocate(i, strlen(expected) + 1);
    strcpy(x->expected[0], expected);
    x->failure = NULL;
    x->recieved = mpc_input_peekc(i);
    return x;
  }
  
  static mpc_err_t *mpc_err_fail(mpc_input_t *i, const char *failure) {
    mpc_err_t *x;
    if (i->suppress) { return NULL; }
    x = mpc_allocate(i, sizeof(mpc_err_t));
    x->filename = mpc_allocate(i, strlen(i->filename) + 1);
    strcpy(x->filename, i->filename);
    x->state = i->state;
    x->expected_num = 0;
    x->expected = NULL;
    x->failure = mpc_allocate(i, strlen(failure) + 1);
    strcpy(x->failure, failure);
    x->recieved = ' ';
    return x;
  }
  
  static mpc_err_t *mpc_err_file(const char *filename, const char *failure) {
    mpc_err_t *x;
    x = allocate(sizeof(mpc_err_t));
    x->filename = allocate(strlen(filename) + 1);
    strcpy(x->filename, filename);
    x->state = mpc_state_new();
    x->expected_num = 0;
    x->expected = NULL;
    x->failure = allocate(strlen(failure) + 1);
    strcpy(x->failure, failure);
    x->recieved = ' ';
    return x;
  }
  
  static void mpc_err_delete_internal(mpc_input_t *i, mpc_err_t *x) {
    int j;
    if (x == NULL) { return; }
    for (j = 0; j < x->expected_num; j++) { mpc_free(i, x->expected[j]); }
    mpc_free(i, x->expected);
    mpc_free(i, x->filename);
    mpc_free(i, x->failure);
    mpc_free(i, x);
  }
  
  static mpc_err_t *mpc_err_export(mpc_input_t *i, mpc_err_t *x) {
    int j;
    for (j = 0; j < x->expected_num; j++) {
      x->expected[j] = mpc_export(i, x->expected[j]);
    }
    x->expected = mpc_export(i, x->expected);
    x->filename = mpc_export(i, x->filename);
    x->failure = mpc_export(i, x->failure);
    return mpc_export(i, x);
  }
  
  static int mpc_err_contains_expected(mpc_input_t *i, mpc_err_t *x, char *expected) {
    int j;
    (void)i;
    for (j = 0; j < x->expected_num; j++) {
      if (strcmp(x->expected[j], expected) == 0) { return 1; }
    }
    return 0;
  }
  
  static void mpc_err_add_expected(mpc_input_t *i, mpc_err_t *x, char *expected) {
    (void)i;
    x->expected_num++;
    x->expected = mpc_reallocate(i, x->expected, sizeof(char*) * x->expected_num);
    x->expected[x->expected_num-1] = mpc_allocate(i, strlen(expected) + 1);
    strcpy(x->expected[x->expected_num-1], expected);
  }
  
  static mpc_err_t *mpc_err_or(mpc_input_t *i, mpc_err_t** x, int n) {
    
    int j, k, fst;
    mpc_err_t *e;
    
    fst = -1;
    for (j = 0; j < n; j++) {
      if (x[j] != NULL) { fst = j; }
    }
    
    if (fst == -1) { return NULL; }
    
    e = mpc_allocate(i, sizeof(mpc_err_t));
    e->state = mpc_state_invalid();
    e->expected_num = 0;
    e->expected = NULL;
    e->failure = NULL;
    e->filename = mpc_allocate(i, strlen(x[fst]->filename)+1);
    strcpy(e->filename, x[fst]->filename);
    
    for (j = 0; j < n; j++) {
      if (x[j] == NULL) { continue; }
      if (x[j]->state.pos > e->state.pos) { e->state = x[j]->state; }
    }
    
    for (j = 0; j < n; j++) {
      if (x[j] == NULL) { continue; }
      if (x[j]->state.pos < e->state.pos) { continue; }
      
      if (x[j]->failure) {
        e->failure = mpc_allocate(i, strlen(x[j]->failure)+1);
        strcpy(e->failure, x[j]->failure);
        break;
      }
      
      e->recieved = x[j]->recieved;
      
      for (k = 0; k < x[j]->expected_num; k++) {
        if (!mpc_err_contains_expected(i, e, x[j]->expected[k])) {
          mpc_err_add_expected(i, e, x[j]->expected[k]);
        }
      }
    }
    
    for (j = 0; j < n; j++) {
      if (x[j] == NULL) { continue; }
      mpc_err_delete_internal(i, x[j]);
    }
    
    return e;
  }
  
  static mpc_err_t *mpc_err_repeat(mpc_input_t *i, mpc_err_t *x, const char *prefix) {
  
    int j = 0;
    size_t l = 0;
    char *expect = NULL;
    
    if (x == NULL) { return NULL; }
    
    if (x->expected_num == 0) {
      expect = mpc_calloc(i, 1, 1);
      x->expected_num = 1;
      x->expected = mpc_reallocate(i, x->expected, sizeof(char*) * x->expected_num);
      x->expected[0] = expect;
      return x;
    }
    
    else if (x->expected_num == 1) {
      expect = mpc_allocate(i, strlen(prefix) + strlen(x->expected[0]) + 1);
      strcpy(expect, prefix);
      strcat(expect, x->expected[0]);
      mpc_free(i, x->expected[0]);
      x->expected[0] = expect;
      return x;
    }
    
    else if (x->expected_num > 1) {
      
      l += strlen(prefix);
      for (j = 0; j < x->expected_num-2; j++) {
        l += strlen(x->expected[j]) + strlen(", ");
      }
      l += strlen(x->expected[x->expected_num-2]);
      l += strlen(" or ");
      l += strlen(x->expected[x->expected_num-1]);
      
      expect = mpc_allocate(i, l + 1);
      
      strcpy(expect, prefix);
      for (j = 0; j < x->expected_num-2; j++) {
        strcat(expect, x->expected[j]); strcat(expect, ", ");
      }
      strcat(expect, x->expected[x->expected_num-2]);
      strcat(expect, " or ");
      strcat(expect, x->expected[x->expected_num-1]);
  
      for (j = 0; j < x->expected_num; j++) { mpc_free(i, x->expected[j]); }
      
      x->expected_num = 1;
      x->expected = mpc_reallocate(i, x->expected, sizeof(char*) * x->expected_num);
      x->expected[0] = expect;
      return x;
    }
    
    return NULL;
  }
  
  static mpc_err_t *mpc_err_many1(mpc_input_t *i, mpc_err_t *x) {
    return mpc_err_repeat(i, x, "one or more of ");
  }
  
  static mpc_err_t *mpc_err_count(mpc_input_t *i, mpc_err_t *x, int n) {
    mpc_err_t *y;
    int digits = n/10 + 1;
    char *prefix;
    prefix = mpc_allocate(i, digits + strlen(" of ") + 1);
    sprintf(prefix, "%i of ", n);
    y = mpc_err_repeat(i, x, prefix);
    mpc_free(i, prefix);
    return y;
  }
  
  static mpc_err_t *mpc_err_merge(mpc_input_t *i, mpc_err_t *x, mpc_err_t *y) {
    mpc_err_t *errs[2];
    errs[0] = x;
    errs[1] = y;
    return mpc_err_or(i, errs, 2);
  }
  
  /*
  ** Parser Type
  */
  
  enum {
    MPC_TYPE_UNDEFINED = 0,
    MPC_TYPE_PASS      = 1,
    MPC_TYPE_FAIL      = 2,
    MPC_TYPE_LIFT      = 3,
    MPC_TYPE_LIFT_VAL  = 4,
    MPC_TYPE_EXPECT    = 5,
    MPC_TYPE_ANCHOR    = 6,
    MPC_TYPE_STATE     = 7,
    
    MPC_TYPE_ANY       = 8,
    MPC_TYPE_SINGLE    = 9,
    MPC_TYPE_ONEOF     = 10,
    MPC_TYPE_NONEOF    = 11,
    MPC_TYPE_RANGE     = 12,
    MPC_TYPE_SATISFY   = 13,
    MPC_TYPE_STRING    = 14,
    
    MPC_TYPE_APPLY     = 15,
    MPC_TYPE_APPLY_TO  = 16,
    MPC_TYPE_PREDICT   = 17,
    MPC_TYPE_NOT       = 18,
    MPC_TYPE_MAYBE     = 19,
    MPC_TYPE_MANY      = 20,
    MPC_TYPE_MANY1     = 21,
    MPC_TYPE_COUNT     = 22,
    
    MPC_TYPE_OR        = 23,
    MPC_TYPE_AND       = 24
  };
  
  typedef struct { char *m; } mpc_pdata_fail_t;
  typedef struct { mpc_ctor_t lf; void *x; } mpc_pdata_lift_t;
  typedef struct { mpc_parser_t *x; char *m; } mpc_pdata_expect_t;
  typedef struct { int(*f)(char,char); } mpc_pdata_anchor_t;
  typedef struct { char x; } mpc_pdata_single_t;
  typedef struct { char x; char y; } mpc_pdata_range_t;
  typedef struct { int(*f)(char); } mpc_pdata_satisfy_t;
  typedef struct { char *x; } mpc_pdata_string_t;
  typedef struct { mpc_parser_t *x; mpc_apply_t f; } mpc_pdata_apply_t;
  typedef struct { mpc_parser_t *x; mpc_apply_to_t f; void *d; } mpc_pdata_apply_to_t;
  typedef struct { mpc_parser_t *x; } mpc_pdata_predict_t;
  typedef struct { mpc_parser_t *x; mpc_dtor_t dx; mpc_ctor_t lf; } mpc_pdata_not_t;
  typedef struct { int n; mpc_fold_t f; mpc_parser_t *x; mpc_dtor_t dx; } mpc_pdata_repeat_t;
  typedef struct { int n; mpc_parser_t **xs; } mpc_pdata_or_t;
  typedef struct { int n; mpc_fold_t f; mpc_parser_t **xs; mpc_dtor_t *dxs;  } mpc_pdata_and_t;
  
  typedef union {
    mpc_pdata_fail_t fail;
    mpc_pdata_lift_t lift;
    mpc_pdata_expect_t expect;
    mpc_pdata_anchor_t anchor;
    mpc_pdata_single_t single;
    mpc_pdata_range_t range;
    mpc_pdata_satisfy_t satisfy;
    mpc_pdata_string_t string;
    mpc_pdata_apply_t apply;
    mpc_pdata_apply_to_t apply_to;
    mpc_pdata_predict_t predict;
    mpc_pdata_not_t not;
    mpc_pdata_repeat_t repeat;
    mpc_pdata_and_t and;
    mpc_pdata_or_t or;
  } mpc_pdata_t;
  
  struct mpc_parser_t {
    char retained;
    char *name;
    char type;
    mpc_pdata_t data;
  };
  
  static mpc_val_t *mpcf_input_nth_free(mpc_input_t *i, int n, mpc_val_t **xs, int x) {
    int j;
    for (j = 0; j < n; j++) { if (j != x) { mpc_free(i, xs[j]); } }
    return xs[x];
  }
   
  static mpc_val_t *mpcf_input_fst_free(mpc_input_t *i, int n, mpc_val_t **xs) { return mpcf_input_nth_free(i, n, xs, 0); }
  static mpc_val_t *mpcf_input_snd_free(mpc_input_t *i, int n, mpc_val_t **xs) { return mpcf_input_nth_free(i, n, xs, 1); }
  static mpc_val_t *mpcf_input_trd_free(mpc_input_t *i, int n, mpc_val_t **xs) { return mpcf_input_nth_free(i, n, xs, 2); }
  
  static mpc_val_t *mpcf_input_strfold(mpc_input_t *i, int n, mpc_val_t **xs) {
    int j;
    size_t l = 0;
    if (n == 0) { return mpc_calloc(i, 1, 1); }
    for (j = 0; j < n; j++) { l += strlen(xs[j]); }
    xs[0] = mpc_reallocate(i, xs[0], l + 1);
    for (j = 1; j < n; j++) { strcat(xs[0], xs[j]); mpc_free(i, xs[j]); }
    return xs[0];
  }
  
  static mpc_val_t *mpcf_input_state_ast(mpc_input_t *i, int n, mpc_val_t **xs) {
    mpc_state_t *s = ((mpc_state_t**)xs)[0];
    mpc_ast_t *a = ((mpc_ast_t**)xs)[1];
    a = mpc_ast_state(a, *s);
    mpc_free(i, s);
    (void) n;
    return a;
  }
  
  static mpc_val_t *mpc_parse_fold(mpc_input_t *i, mpc_fold_t f, int n, mpc_val_t **xs) {
    int j;
    if (f == mpcf_null)      { return mpcf_null(n, xs); }
    if (f == mpcf_fst)       { return mpcf_fst(n, xs); }
    if (f == mpcf_snd)       { return mpcf_snd(n, xs); }
    if (f == mpcf_trd)       { return mpcf_trd(n, xs); }
    if (f == mpcf_fst_free)  { return mpcf_input_fst_free(i, n, xs); }
    if (f == mpcf_snd_free)  { return mpcf_input_snd_free(i, n, xs); }
    if (f == mpcf_trd_free)  { return mpcf_input_trd_free(i, n, xs); }
    if (f == mpcf_strfold)   { return mpcf_input_strfold(i, n, xs); }
    if (f == mpcf_state_ast) { return mpcf_input_state_ast(i, n, xs); }
    for (j = 0; j < n; j++) { xs[j] = mpc_export(i, xs[j]); }
    return f(j, xs);
  }
  
  static mpc_val_t *mpcf_input_free(mpc_input_t *i, mpc_val_t *x) {
    mpc_free(i, x);
    return NULL;
  }
  
  static mpc_val_t *mpcf_input_str_ast(mpc_input_t *i, mpc_val_t *c) {
    mpc_ast_t *a = mpc_ast_new("", c);
    mpc_free(i, c);
    return a;
  }
  
  static mpc_val_t *mpc_parse_apply(mpc_input_t *i, mpc_apply_t f, mpc_val_t *x) {
    if (f == mpcf_free)     { return mpcf_input_free(i, x); }
    if (f == mpcf_str_ast)  { return mpcf_input_str_ast(i, x); }
    return f(mpc_export(i, x));
  }
  
  static mpc_val_t *mpc_parse_apply_to(mpc_input_t *i, mpc_apply_to_t f, mpc_val_t *x, mpc_val_t *d) {
    return f(mpc_export(i, x), d);
  }
  
  static void mpc_parse_dtor(mpc_input_t *i, mpc_dtor_t d, mpc_val_t *x) {
    if (d == free) { mpc_free(i, x); return; }
    d(mpc_export(i, x));
  }
  
  enum {
    MPC_PARSE_STACK_MIN = 4
  };
  
  #define MPC_SUCCESS(x) r->output = x; return 1
  #define MPC_FAILURE(x) r->error = x; return 0
  #define MPC_PRIMITIVE(x) \
    if (x) { MPC_SUCCESS(r->output); } \
    else { MPC_FAILURE(NULL); }
  
  static int mpc_parse_run(mpc_input_t *i, mpc_parser_t *p, mpc_result_t *r, mpc_err_t **e) {
    
    int j = 0, k = 0;
    mpc_result_t results_stk[MPC_PARSE_STACK_MIN];
    mpc_result_t *results;
    int results_slots = MPC_PARSE_STACK_MIN;
    
    switch (p->type) {
        
      /* Basic Parsers */
  
      case MPC_TYPE_ANY:     MPC_PRIMITIVE(mpc_input_any(i, (char**)&r->output));
      case MPC_TYPE_SINGLE:  MPC_PRIMITIVE(mpc_input_char(i, p->data.single.x, (char**)&r->output));
      case MPC_TYPE_RANGE:   MPC_PRIMITIVE(mpc_input_range(i, p->data.range.x, p->data.range.y, (char**)&r->output));
      case MPC_TYPE_ONEOF:   MPC_PRIMITIVE(mpc_input_oneof(i, p->data.string.x, (char**)&r->output));
      case MPC_TYPE_NONEOF:  MPC_PRIMITIVE(mpc_input_noneof(i, p->data.string.x, (char**)&r->output));
      case MPC_TYPE_SATISFY: MPC_PRIMITIVE(mpc_input_satisfy(i, p->data.satisfy.f, (char**)&r->output));
      case MPC_TYPE_STRING:  MPC_PRIMITIVE(mpc_input_string(i, p->data.string.x, (char**)&r->output));
      case MPC_TYPE_ANCHOR:  MPC_PRIMITIVE(mpc_input_anchor(i, p->data.anchor.f, (char**)&r->output));
      
      /* Other parsers */
      
      case MPC_TYPE_UNDEFINED: MPC_FAILURE(mpc_err_fail(i, "Parser Undefined!"));
      case MPC_TYPE_PASS:      MPC_SUCCESS(NULL);
      case MPC_TYPE_FAIL:      MPC_FAILURE(mpc_err_fail(i, p->data.fail.m));
      case MPC_TYPE_LIFT:      MPC_SUCCESS(p->data.lift.lf());
      case MPC_TYPE_LIFT_VAL:  MPC_SUCCESS(p->data.lift.x);
      case MPC_TYPE_STATE:     MPC_SUCCESS(mpc_input_state_copy(i));
      
      /* Application Parsers */
      
      case MPC_TYPE_APPLY:
        if (mpc_parse_run(i, p->data.apply.x, r, e)) {
          MPC_SUCCESS(mpc_parse_apply(i, p->data.apply.f, r->output));
        } else {
          MPC_FAILURE(r->output);
        }
      
      case MPC_TYPE_APPLY_TO:
        if (mpc_parse_run(i, p->data.apply_to.x, r, e)) {
          MPC_SUCCESS(mpc_parse_apply_to(i, p->data.apply_to.f, r->output, p->data.apply_to.d));
        } else {
          MPC_FAILURE(r->error);
        }
      
      case MPC_TYPE_EXPECT:
        mpc_input_suppress_enable(i);
        if (mpc_parse_run(i, p->data.expect.x, r, e)) {
          mpc_input_suppress_disable(i);
          MPC_SUCCESS(r->output);
        } else {
          mpc_input_suppress_disable(i);
          MPC_FAILURE(mpc_err_new(i, p->data.expect.m));
        }
      
      case MPC_TYPE_PREDICT:
        mpc_input_backtrack_disable(i);
        if (mpc_parse_run(i, p->data.predict.x, r, e)) {      
          mpc_input_backtrack_enable(i);
          MPC_SUCCESS(r->output);
        } else {
          mpc_input_backtrack_enable(i);
          MPC_FAILURE(r->error);
        }
      
      /* Optional Parsers */
      
      /* TODO: Update Not Error Message */
      
      case MPC_TYPE_NOT:
        mpc_input_mark(i);
        mpc_input_suppress_enable(i);
        if (mpc_parse_run(i, p->data.not.x, r, e)) {
          mpc_input_rewind(i);
          mpc_input_suppress_disable(i);
          mpc_parse_dtor(i, p->data.not.dx, r->output);
          MPC_FAILURE(mpc_err_new(i, "opposite"));
        } else {
          mpc_input_unmark(i);
          mpc_input_suppress_disable(i);
          MPC_SUCCESS(p->data.not.lf());
        }
      
      case MPC_TYPE_MAYBE:
        if (mpc_parse_run(i, p->data.not.x, r, e)) {
          MPC_SUCCESS(r->output);
        } else {
          *e = mpc_err_merge(i, *e, r->error);
          MPC_SUCCESS(p->data.not.lf());
        }
      
      /* Repeat Parsers */
      
      case MPC_TYPE_MANY:
        
        results = results_stk;
        
        while (mpc_parse_run(i, p->data.repeat.x, &results[j], e)) {
          j++;
          if (j == MPC_PARSE_STACK_MIN) {
            results_slots = j + j / 2;
            results = mpc_allocate(i, sizeof(mpc_result_t) * results_slots);
            memcpy(results, results_stk, sizeof(mpc_result_t) * MPC_PARSE_STACK_MIN);
          } else if (j >= results_slots) {
            results_slots = j + j / 2;
            results = mpc_reallocate(i, results, sizeof(mpc_result_t) * results_slots);
          }
        }
        
        *e = mpc_err_merge(i, *e, results[j].error);
        MPC_SUCCESS(
          mpc_parse_fold(i, p->data.repeat.f, j, (mpc_val_t**)results);
          if (j >= MPC_PARSE_STACK_MIN) { mpc_free(i, results); });
      
      case MPC_TYPE_MANY1:
        
        results = results_stk;
        
        while (mpc_parse_run(i, p->data.repeat.x, &results[j], e)) {
          j++;
          if (j == MPC_PARSE_STACK_MIN) {
            results_slots = j + j / 2;
            results = mpc_allocate(i, sizeof(mpc_result_t) * results_slots);
            memcpy(results, results_stk, sizeof(mpc_result_t) * MPC_PARSE_STACK_MIN);
          } else if (j >= results_slots) {
            results_slots = j + j / 2;
            results = mpc_reallocate(i, results, sizeof(mpc_result_t) * results_slots);
          }
        }
        
        if (j == 0) {
          MPC_FAILURE(
            mpc_err_many1(i, results[j].error);
            if (j >= MPC_PARSE_STACK_MIN) { mpc_free(i, results); });
        } else {
          *e = mpc_err_merge(i, *e, results[j].error);
          MPC_SUCCESS(
            mpc_parse_fold(i, p->data.repeat.f, j, (mpc_val_t**)results);
            if (j >= MPC_PARSE_STACK_MIN) { mpc_free(i, results); });
        }
      
      case MPC_TYPE_COUNT:
        
        results = p->data.repeat.n > MPC_PARSE_STACK_MIN
          ? mpc_allocate(i, sizeof(mpc_result_t) * p->data.repeat.n)
          : results_stk;
        
        while (mpc_parse_run(i, p->data.repeat.x, &results[j], e)) {
          j++;
          if (j == p->data.repeat.n) { break; }
        }
        
        if (j == p->data.repeat.n) {
          MPC_SUCCESS(
            mpc_parse_fold(i, p->data.repeat.f, j, (mpc_val_t**)results);
            if (p->data.repeat.n > MPC_PARSE_STACK_MIN) { mpc_free(i, results); });
        } else {
          for (k = 0; k < j; k++) {
            mpc_parse_dtor(i, p->data.repeat.dx, results[k].output);
          }
          MPC_FAILURE(
            mpc_err_count(i, results[j].error, p->data.repeat.n);
            if (p->data.repeat.n > MPC_PARSE_STACK_MIN) { mpc_free(i, results); });  
        }
        
      /* Combinatory Parsers */
      
      case MPC_TYPE_OR:
        
        if (p->data.or.n == 0) { MPC_SUCCESS(NULL); }
        
        results = p->data.or.n > MPC_PARSE_STACK_MIN
          ? mpc_allocate(i, sizeof(mpc_result_t) * p->data.or.n)
          : results_stk;
        
        for (j = 0; j < p->data.or.n; j++) {
          if (mpc_parse_run(i, p->data.or.xs[j], &results[j], e)) {
            MPC_SUCCESS(results[j].output;
              if (p->data.or.n > MPC_PARSE_STACK_MIN) { mpc_free(i, results); });
          } else {
            *e = mpc_err_merge(i, *e, results[j].error);
          } 
        }
        
        MPC_FAILURE(NULL;
          if (p->data.or.n > MPC_PARSE_STACK_MIN) { mpc_free(i, results); });
      
      case MPC_TYPE_AND:
        
        if (p->data.and.n == 0) { MPC_SUCCESS(NULL); }
        
        results = p->data.or.n > MPC_PARSE_STACK_MIN
          ? mpc_allocate(i, sizeof(mpc_result_t) * p->data.or.n)
          : results_stk;
        
        mpc_input_mark(i);
        for (j = 0; j < p->data.and.n; j++) {
          if (!mpc_parse_run(i, p->data.and.xs[j], &results[j], e)) {
            mpc_input_rewind(i);
            for (k = 0; k < j; k++) {
              mpc_parse_dtor(i, p->data.and.dxs[k], results[k].output);
            }
            MPC_FAILURE(results[j].error;
              if (p->data.or.n > MPC_PARSE_STACK_MIN) { mpc_free(i, results); });
          }
        }
        mpc_input_unmark(i); 
        MPC_SUCCESS(
          mpc_parse_fold(i, p->data.and.f, j, (mpc_val_t**)results);
          if (p->data.or.n > MPC_PARSE_STACK_MIN) { mpc_free(i, results); });
      
      /* End */
      
      default:
        
        MPC_FAILURE(mpc_err_fail(i, "Unknown Parser Type Id!"));
    }
    
    return 0;
    
  }
  
  #undef MPC_SUCCESS
  #undef MPC_FAILURE
  #undef MPC_PRIMITIVE
  
  int mpc_parse_input(mpc_input_t *i, mpc_parser_t *p, mpc_result_t *r) {
    int x;
    mpc_err_t *e = mpc_err_fail(i, "Unknown Error");
    e->state = mpc_state_invalid();
    x = mpc_parse_run(i, p, r, &e);
    if (x) {
      mpc_err_delete_internal(i, e);
      r->output = mpc_export(i, r->output);
    } else {
      r->error = mpc_err_export(i, mpc_err_merge(i, e, r->error));
    }
    return x;
  }
  
  int mpc_parse(const char *filename, const char *string, mpc_parser_t *p, mpc_result_t *r) {
    int x;
    mpc_input_t *i = mpc_input_new_string(filename, string);
    x = mpc_parse_input(i, p, r);
    mpc_input_delete(i);
    return x;
  }
  
  int mpc_nparse(const char *filename, const char *string, size_t length, mpc_parser_t *p, mpc_result_t *r) {
    int x;
    mpc_input_t *i = mpc_input_new_nstring(filename, string, length);
    x = mpc_parse_input(i, p, r);
    mpc_input_delete(i);
    return x;
  }
  
  int mpc_parse_file(const char *filename, FILE *file, mpc_parser_t *p, mpc_result_t *r) {
    int x;
    mpc_input_t *i = mpc_input_new_file(filename, file);
    x = mpc_parse_input(i, p, r);
    mpc_input_delete(i);
    return x;
  }
  
  int mpc_parse_pipe(const char *filename, FILE *pipe, mpc_parser_t *p, mpc_result_t *r) {
    int x;
    mpc_input_t *i = mpc_input_new_pipe(filename, pipe);
    x = mpc_parse_input(i, p, r);
    mpc_input_delete(i);
    return x;
  }
  
  int mpc_parse_contents(const char *filename, mpc_parser_t *p, mpc_result_t *r) {
    
    FILE *f = fopen(filename, "rb");
    int res;
    
    if (f == NULL) {
      r->output = NULL;
      r->error = mpc_err_file(filename, "Unable to open file!");
      return 0;
    }
    
    res = mpc_parse_file(filename, f, p, r);
    fclose(f);
    return res;
  }
  
  /*
  ** Building a Parser
  */
  
  static void mpc_undefine_unretained(mpc_parser_t *p, int force);
  
  static void mpc_undefine_or(mpc_parser_t *p) {
    
    int i;
    for (i = 0; i < p->data.or.n; i++) {
      mpc_undefine_unretained(p->data.or.xs[i], 0);
    }
    free(p->data.or.xs);
    
  }
  
  static void mpc_undefine_and(mpc_parser_t *p) {
    
    int i;
    for (i = 0; i < p->data.and.n; i++) {
      mpc_undefine_unretained(p->data.and.xs[i], 0);
    }
    free(p->data.and.xs);
    free(p->data.and.dxs);
    
  }
  
  static void mpc_undefine_unretained(mpc_parser_t *p, int force) {
    
    if (p->retained && !force) { return; }
    
    switch (p->type) {
      
      case MPC_TYPE_FAIL: free(p->data.fail.m); break;
      
      case MPC_TYPE_ONEOF: 
      case MPC_TYPE_NONEOF:
      case MPC_TYPE_STRING:
        free(p->data.string.x); 
        break;
      
      case MPC_TYPE_APPLY:    mpc_undefine_unretained(p->data.apply.x, 0);    break;
      case MPC_TYPE_APPLY_TO: mpc_undefine_unretained(p->data.apply_to.x, 0); break;
      case MPC_TYPE_PREDICT:  mpc_undefine_unretained(p->data.predict.x, 0);  break;
      
      case MPC_TYPE_MAYBE:
      case MPC_TYPE_NOT:
        mpc_undefine_unretained(p->data.not.x, 0);
        break;
      
      case MPC_TYPE_EXPECT:
        mpc_undefine_unretained(p->data.expect.x, 0);
        free(p->data.expect.m);
        break;
        
      case MPC_TYPE_MANY:
      case MPC_TYPE_MANY1:
      case MPC_TYPE_COUNT:
        mpc_undefine_unretained(p->data.repeat.x, 0);
        break;
      
      case MPC_TYPE_OR:  mpc_undefine_or(p);  break;
      case MPC_TYPE_AND: mpc_undefine_and(p); break;
      
      default: break;
    }
    
    if (!force) {
      free(p->name);
      free(p);
    }
    
  }
  
  void mpc_delete(mpc_parser_t *p) {
    if (p->retained) {
  
      if (p->type != MPC_TYPE_UNDEFINED) {
        mpc_undefine_unretained(p, 0);
      } 
      
      free(p->name);
      free(p);
    
    } else {
      mpc_undefine_unretained(p, 0);  
    }
  }
  
  static void mpc_soft_delete(mpc_val_t *x) {
    mpc_undefine_unretained(x, 0);
  }
  
  static mpc_parser_t *mpc_undefined(void) {
    mpc_parser_t *p = calloc(1, sizeof(mpc_parser_t));
    p->retained = 0;
    p->type = MPC_TYPE_UNDEFINED;
    p->name = NULL;
    return p;
  }
  
  mpc_parser_t *mpc_new(const char *name) {
    mpc_parser_t *p = mpc_undefined();
    p->retained = 1;
    p->name = reallocate(p->name, strlen(name) + 1);
    strcpy(p->name, name);
    return p;
  }
  
  mpc_parser_t *mpc_copy(mpc_parser_t *a) {
    int i = 0;
    mpc_parser_t *p;
    
    if (a->retained) { return a; }
    
    p = mpc_undefined();
    p->retained = a->retained;
    p->type = a->type;
    p->data = a->data;
    
    if (a->name) {
      p->name = allocate(strlen(a->name)+1);
      strcpy(p->name, a->name);
    }
    
    switch (a->type) {
      
      case MPC_TYPE_FAIL:
        p->data.fail.m = allocate(strlen(a->data.fail.m)+1);
        strcpy(p->data.fail.m, a->data.fail.m);
      break;
      
      case MPC_TYPE_ONEOF: 
      case MPC_TYPE_NONEOF:
      case MPC_TYPE_STRING:
        p->data.string.x = allocate(strlen(a->data.string.x)+1);
        strcpy(p->data.string.x, a->data.string.x);
        break;
      
      case MPC_TYPE_APPLY:    p->data.apply.x    = mpc_copy(a->data.apply.x);    break;
      case MPC_TYPE_APPLY_TO: p->data.apply_to.x = mpc_copy(a->data.apply_to.x); break;
      case MPC_TYPE_PREDICT:  p->data.predict.x  = mpc_copy(a->data.predict.x);  break;
      
      case MPC_TYPE_MAYBE:
      case MPC_TYPE_NOT:
        p->data.not.x = mpc_copy(a->data.not.x);
        break;
      
      case MPC_TYPE_EXPECT:
        p->data.expect.x = mpc_copy(a->data.expect.x);
        p->data.expect.m = allocate(strlen(a->data.expect.m)+1);
        strcpy(p->data.expect.m, a->data.expect.m);
        break;
        
      case MPC_TYPE_MANY:
      case MPC_TYPE_MANY1:
      case MPC_TYPE_COUNT:
        p->data.repeat.x = mpc_copy(a->data.repeat.x);
        break;
      
      case MPC_TYPE_OR:
        p->data.or.xs = allocate(a->data.or.n * sizeof(mpc_parser_t*));
        for (i = 0; i < a->data.or.n; i++) {
          p->data.or.xs[i] = mpc_copy(a->data.or.xs[i]);
        }
      break;
      case MPC_TYPE_AND:
        p->data.and.xs = allocate(a->data.and.n * sizeof(mpc_parser_t*));
        for (i = 0; i < a->data.and.n; i++) {
          p->data.and.xs[i] = mpc_copy(a->data.and.xs[i]);
        }
        p->data.and.dxs = allocate((a->data.and.n-1) * sizeof(mpc_dtor_t));
        for (i = 0; i < a->data.and.n-1; i++) {
          p->data.and.dxs[i] = a->data.and.dxs[i];
        }
      break;
      
      default: break;
    }
  
    
    return p;
  }
  
  mpc_parser_t *mpc_undefine(mpc_parser_t *p) {
    mpc_undefine_unretained(p, 1);
    p->type = MPC_TYPE_UNDEFINED;
    return p;
  }
  
  mpc_parser_t *mpc_define(mpc_parser_t *p, mpc_parser_t *a) {
    
    if (p->retained) {
      p->type = a->type;
      p->data = a->data;
    } else {
      mpc_parser_t *a2 = mpc_failf("Attempt to assign to Unretained Parser!");
      p->type = a2->type;
      p->data = a2->data;
      free(a2);
    }
    
    free(a);
    return p;  
  }
  
  void mpc_cleanup(int n, ...) {
    int i;
    mpc_parser_t **list = allocate(sizeof(mpc_parser_t*) * n);
    
    va_list va;
    va_start(va, n);
    for (i = 0; i < n; i++) { list[i] = va_arg(va, mpc_parser_t*); }
    for (i = 0; i < n; i++) { mpc_undefine(list[i]); }
    for (i = 0; i < n; i++) { mpc_delete(list[i]); }  
    va_end(va);  
  
    free(list);
  }
  
  mpc_parser_t *mpc_pass(void) {
    mpc_parser_t *p = mpc_undefined();
    p->type = MPC_TYPE_PASS;
    return p;
  }
  
  mpc_parser_t *mpc_fail(const char *m) {
    mpc_parser_t *p = mpc_undefined();
    p->type = MPC_TYPE_FAIL;
    p->data.fail.m = allocate(strlen(m) + 1);
    strcpy(p->data.fail.m, m);
    return p;
  }
  
  /*
  ** As `snprintf` is not ANSI standard this 
  ** function `mpc_failf` should be considered
  ** unsafe.
  **
  ** You have a few options if this is going to be
  ** trouble.
  **
  ** - Ensure the format string does not exceed
  **   the buffer length using precision specifiers
  **   such as `%.512s`.
  **
  ** - Patch this function in your code base to 
  **   use `snprintf` or whatever variant your
  **   system supports.
  **
  ** - Avoid it altogether.
  **
  */
  
  mpc_parser_t *mpc_failf(const char *fmt, ...) {
    
    va_list va;
    char *buffer;
  
    mpc_parser_t *p = mpc_undefined();
    p->type = MPC_TYPE_FAIL;
    
    va_start(va, fmt);
    buffer = allocate(2048);
    vsprintf(buffer, fmt, va);
    va_end(va);
    
    buffer = reallocate(buffer, strlen(buffer) + 1);
    p->data.fail.m = buffer;
    return p;
  
  }
  
  mpc_parser_t *mpc_lift_val(mpc_val_t *x) {
    mpc_parser_t *p = mpc_undefined();
    p->type = MPC_TYPE_LIFT_VAL;
    p->data.lift.x = x;
    return p;
  }
  
  mpc_parser_t *mpc_lift(mpc_ctor_t lf) {
    mpc_parser_t *p = mpc_undefined();
    p->type = MPC_TYPE_LIFT;
    p->data.lift.lf = lf;
    return p;
  }
  
  mpc_parser_t *mpc_anchor(int(*f)(char,char)) {
    mpc_parser_t *p = mpc_undefined();
    p->type = MPC_TYPE_ANCHOR;
    p->data.anchor.f = f;
    return mpc_expect(p, "anchor");
  }
  
  mpc_parser_t *mpc_state(void) {
    mpc_parser_t *p = mpc_undefined();
    p->type = MPC_TYPE_STATE;
    return p;
  }
  
  mpc_parser_t *mpc_expect(mpc_parser_t *a, const char *expected) {
    mpc_parser_t *p = mpc_undefined();
    p->type = MPC_TYPE_EXPECT;
    p->data.expect.x = a;
    p->data.expect.m = allocate(strlen(expected) + 1);
    strcpy(p->data.expect.m, expected);
    return p;
  }
  
  /*
  ** As `snprintf` is not ANSI standard this 
  ** function `mpc_expectf` should be considered
  ** unsafe.
  **
  ** You have a few options if this is going to be
  ** trouble.
  **
  ** - Ensure the format string does not exceed
  **   the buffer length using precision specifiers
  **   such as `%.512s`.
  **
  ** - Patch this function in your code base to 
  **   use `snprintf` or whatever variant your
  **   system supports.
  **
  ** - Avoid it altogether.
  **
  */
  
  mpc_parser_t *mpc_expectf(mpc_parser_t *a, const char *fmt, ...) {
    va_list va;
    char *buffer;
  
    mpc_parser_t *p = mpc_undefined();
    p->type = MPC_TYPE_EXPECT;
    
    va_start(va, fmt);
    buffer = allocate(2048);
    vsprintf(buffer, fmt, va);
    va_end(va);
    
    buffer = reallocate(buffer, strlen(buffer) + 1);
    p->data.expect.x = a;
    p->data.expect.m = buffer;
    return p;
  }
  
  /*
  ** Basic Parsers
  */
  
  mpc_parser_t *mpc_any(void) {
    mpc_parser_t *p = mpc_undefined();
    p->type = MPC_TYPE_ANY;
    return mpc_expect(p, "any character");
  }
  
  mpc_parser_t *mpc_char(char c) {
    mpc_parser_t *p = mpc_undefined();
    p->type = MPC_TYPE_SINGLE;
    p->data.single.x = c;
    return mpc_expectf(p, "'%c'", c);
  }
  
  mpc_parser_t *mpc_range(char s, char e) {
    mpc_parser_t *p = mpc_undefined();
    p->type = MPC_TYPE_RANGE;
    p->data.range.x = s;
    p->data.range.y = e;
    return mpc_expectf(p, "character between '%c' and '%c'", s, e);
  }
  
  mpc_parser_t *mpc_oneof(const char *s) {
    mpc_parser_t *p = mpc_undefined();
    p->type = MPC_TYPE_ONEOF;
    p->data.string.x = allocate(strlen(s) + 1);
    strcpy(p->data.string.x, s);
    return mpc_expectf(p, "one of '%s'", s);
  }
  
  mpc_parser_t *mpc_noneof(const char *s) {
    mpc_parser_t *p = mpc_undefined();
    p->type = MPC_TYPE_NONEOF;
    p->data.string.x = allocate(strlen(s) + 1);
    strcpy(p->data.string.x, s);
    return mpc_expectf(p, "none of '%s'", s);
  
  }
  
  mpc_parser_t *mpc_satisfy(int(*f)(char)) {
    mpc_parser_t *p = mpc_undefined();
    p->type = MPC_TYPE_SATISFY;
    p->data.satisfy.f = f;
    return mpc_expectf(p, "character satisfying function %p", f);
  }
  
  mpc_parser_t *mpc_string(const char *s) {
    mpc_parser_t *p = mpc_undefined();
    p->type = MPC_TYPE_STRING;
    p->data.string.x = allocate(strlen(s) + 1);
    strcpy(p->data.string.x, s);
    return mpc_expectf(p, "\"%s\"", s);
  }
  
  /*
  ** Core Parsers
  */
  
  mpc_parser_t *mpc_apply(mpc_parser_t *a, mpc_apply_t f) {
    mpc_parser_t *p = mpc_undefined();
    p->type = MPC_TYPE_APPLY;
    p->data.apply.x = a;
    p->data.apply.f = f;
    return p;
  }
  
  mpc_parser_t *mpc_apply_to(mpc_parser_t *a, mpc_apply_to_t f, void *x) {
    mpc_parser_t *p = mpc_undefined();
    p->type = MPC_TYPE_APPLY_TO;
    p->data.apply_to.x = a;
    p->data.apply_to.f = f;
    p->data.apply_to.d = x;
    return p;
  }
  
  mpc_parser_t *mpc_predictive(mpc_parser_t *a) {
    mpc_parser_t *p = mpc_undefined();
    p->type = MPC_TYPE_PREDICT;
    p->data.predict.x = a;
    return p;
  }
  
  mpc_parser_t *mpc_not_lift(mpc_parser_t *a, mpc_dtor_t da, mpc_ctor_t lf) {
    mpc_parser_t *p = mpc_undefined();
    p->type = MPC_TYPE_NOT;
    p->data.not.x = a;
    p->data.not.dx = da;
    p->data.not.lf = lf;
    return p;
  }
  
  mpc_parser_t *mpc_not(mpc_parser_t *a, mpc_dtor_t da) {
    return mpc_not_lift(a, da, mpcf_ctor_null);
  }
  
  mpc_parser_t *mpc_maybe_lift(mpc_parser_t *a, mpc_ctor_t lf) {
    mpc_parser_t *p = mpc_undefined();
    p->type = MPC_TYPE_MAYBE;
    p->data.not.x = a;
    p->data.not.lf = lf;
    return p;
  }
  
  mpc_parser_t *mpc_maybe(mpc_parser_t *a) {
    return mpc_maybe_lift(a, mpcf_ctor_null);
  }
  
  mpc_parser_t *mpc_many(mpc_fold_t f, mpc_parser_t *a) {
    mpc_parser_t *p = mpc_undefined();
    p->type = MPC_TYPE_MANY;
    p->data.repeat.x = a;
    p->data.repeat.f = f;
    return p;
  }
  
  mpc_parser_t *mpc_many1(mpc_fold_t f, mpc_parser_t *a) {
    mpc_parser_t *p = mpc_undefined();
    p->type = MPC_TYPE_MANY1;
    p->data.repeat.x = a;
    p->data.repeat.f = f;
    return p;
  }
  
  mpc_parser_t *mpc_count(int n, mpc_fold_t f, mpc_parser_t *a, mpc_dtor_t da) {
    mpc_parser_t *p = mpc_undefined();
    p->type = MPC_TYPE_COUNT;
    p->data.repeat.n = n;
    p->data.repeat.f = f;
    p->data.repeat.x = a;
    p->data.repeat.dx = da;
    return p;
  }
  
  mpc_parser_t *mpc_or(int n, ...) {
  
    int i;
    va_list va;
  
    mpc_parser_t *p = mpc_undefined();
    
    p->type = MPC_TYPE_OR;
    p->data.or.n = n;
    p->data.or.xs = allocate(sizeof(mpc_parser_t*) * n);
    
    va_start(va, n);  
    for (i = 0; i < n; i++) {
      p->data.or.xs[i] = va_arg(va, mpc_parser_t*);
    }
    va_end(va);
    
    return p;
  }
  
  mpc_parser_t *mpc_and(int n, mpc_fold_t f, ...) {
  
    int i;
    va_list va;
  
    mpc_parser_t *p = mpc_undefined();
    
    p->type = MPC_TYPE_AND;
    p->data.and.n = n;
    p->data.and.f = f;
    p->data.and.xs = allocate(sizeof(mpc_parser_t*) * n);
    p->data.and.dxs = allocate(sizeof(mpc_dtor_t) * (n-1));
  
    va_start(va, f);  
    for (i = 0; i < n; i++) {
      p->data.and.xs[i] = va_arg(va, mpc_parser_t*);
    }
    for (i = 0; i < (n-1); i++) {
      p->data.and.dxs[i] = va_arg(va, mpc_dtor_t);
    }  
    va_end(va);
    
    return p;
  }
  
  /*
  ** Common Parsers
  */
  
  static int mpc_soi_anchor(char prev, char next) { (void) next; return (prev == '\0'); }
  static int mpc_eoi_anchor(char prev, char next) { (void) prev; return (next == '\0'); }
  
  mpc_parser_t *mpc_soi(void) { return mpc_expect(mpc_anchor(mpc_soi_anchor), "start of input"); }
  mpc_parser_t *mpc_eoi(void) { return mpc_expect(mpc_anchor(mpc_eoi_anchor), "end of input"); }
  
  static int mpc_boundary_anchor(char prev, char next) {
    const char* word = "abcdefghijklmnopqrstuvwxyz"
                       "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
                       "0123456789_";
    if ( strchr(word, next) &&  prev == '\0') { return 1; }
    if ( strchr(word, prev) &&  next == '\0') { return 1; }
    if ( strchr(word, next) && !strchr(word, prev)) { return 1; }
    if (!strchr(word, next) &&  strchr(word, prev)) { return 1; }
    return 0;
  }
  
  mpc_parser_t *mpc_boundary(void) { return mpc_expect(mpc_anchor(mpc_boundary_anchor), "boundary"); }
  
  mpc_parser_t *mpc_whitespace(void) { return mpc_expect(mpc_oneof(" \f\n\r\t\v"), "whitespace"); }
  mpc_parser_t *mpc_whitespaces(void) { return mpc_expect(mpc_many(mpcf_strfold, mpc_whitespace()), "spaces"); }
  mpc_parser_t *mpc_blank(void) { return mpc_expect(mpc_apply(mpc_whitespaces(), mpcf_free), "whitespace"); }
  
  mpc_parser_t *mpc_newline(void) { return mpc_expect(mpc_char('\n'), "newline"); }
  mpc_parser_t *mpc_tab(void) { return mpc_expect(mpc_char('\t'), "tab"); }
  mpc_parser_t *mpc_escape(void) { return mpc_and(2, mpcf_strfold, mpc_char('\\'), mpc_any(), free); }
  
  mpc_parser_t *mpc_digit(void) { return mpc_expect(mpc_oneof("0123456789"), "digit"); }
  mpc_parser_t *mpc_hexdigit(void) { return mpc_expect(mpc_oneof("0123456789ABCDEFabcdef"), "hex digit"); }
  mpc_parser_t *mpc_octdigit(void) { return mpc_expect(mpc_oneof("01234567"), "oct digit"); }
  mpc_parser_t *mpc_digits(void) { return mpc_expect(mpc_many1(mpcf_strfold, mpc_digit()), "digits"); }
  mpc_parser_t *mpc_hexdigits(void) { return mpc_expect(mpc_many1(mpcf_strfold, mpc_hexdigit()), "hex digits"); }
  mpc_parser_t *mpc_octdigits(void) { return mpc_expect(mpc_many1(mpcf_strfold, mpc_octdigit()), "oct digits"); }
  
  mpc_parser_t *mpc_lower(void) { return mpc_expect(mpc_oneof("abcdefghijklmnopqrstuvwxyz"), "lowercase letter"); }
  mpc_parser_t *mpc_upper(void) { return mpc_expect(mpc_oneof("ABCDEFGHIJKLMNOPQRSTUVWXYZ"), "uppercase letter"); }
  mpc_parser_t *mpc_alpha(void) { return mpc_expect(mpc_oneof("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"), "letter"); }
  mpc_parser_t *mpc_underscore(void) { return mpc_expect(mpc_char('_'), "underscore"); }
  mpc_parser_t *mpc_alphanum(void) { return mpc_expect(mpc_or(3, mpc_alpha(), mpc_digit(), mpc_underscore()), "alphanumeric"); }
  
  mpc_parser_t *mpc_int(void) { return mpc_expect(mpc_apply(mpc_digits(), mpcf_int), "integer"); }
  mpc_parser_t *mpc_hex(void) { return mpc_expect(mpc_apply(mpc_hexdigits(), mpcf_hex), "hexadecimal"); }
  mpc_parser_t *mpc_oct(void) { return mpc_expect(mpc_apply(mpc_octdigits(), mpcf_oct), "octadecimal"); }
  mpc_parser_t *mpc_number(void) { return mpc_expect(mpc_or(3, mpc_int(), mpc_hex(), mpc_oct()), "number"); }
  
  mpc_parser_t *mpc_real(void) {
  
    /* [+-]?\d+(\.\d+)?([eE][+-]?[0-9]+)? */
    
    mpc_parser_t *p0, *p1, *p2, *p30, *p31, *p32, *p3;
    
    p0 = mpc_maybe_lift(mpc_oneof("+-"), mpcf_ctor_str);
    p1 = mpc_digits();
    p2 = mpc_maybe_lift(mpc_and(2, mpcf_strfold, mpc_char('.'), mpc_digits(), free), mpcf_ctor_str);
    p30 = mpc_oneof("eE");
    p31 = mpc_maybe_lift(mpc_oneof("+-"), mpcf_ctor_str);
    p32 = mpc_digits();
    p3 = mpc_maybe_lift(mpc_and(3, mpcf_strfold, p30, p31, p32, free, free), mpcf_ctor_str);
    
    return mpc_expect(mpc_and(4, mpcf_strfold, p0, p1, p2, p3, free, free, free), "real");
  
  }
  
  mpc_parser_t *mpc_float(void) {
    return mpc_expect(mpc_apply(mpc_real(), mpcf_float), "float");
  }
  
  mpc_parser_t *mpc_char_lit(void) {
    return mpc_expect(mpc_between(mpc_or(2, mpc_escape(), mpc_any()), free, "'", "'"), "char");
  }
  
  mpc_parser_t *mpc_string_lit(void) {
    mpc_parser_t *strchar = mpc_or(2, mpc_escape(), mpc_noneof("\""));
    return mpc_expect(mpc_between(mpc_many(mpcf_strfold, strchar), free, "\"", "\""), "string");
  }
  
  mpc_parser_t *mpc_regex_lit(void) {  
    mpc_parser_t *regexchar = mpc_or(2, mpc_escape(), mpc_noneof("/"));
    return mpc_expect(mpc_between(mpc_many(mpcf_strfold, regexchar), free, "/", "/"), "regex");
  }
  
  mpc_parser_t *mpc_ident(void) {
    mpc_parser_t *p0, *p1; 
    p0 = mpc_or(2, mpc_alpha(), mpc_underscore());
    p1 = mpc_many(mpcf_strfold, mpc_alphanum()); 
    return mpc_and(2, mpcf_strfold, p0, p1, free);
  }
  
  /*
  ** Useful Parsers
  */
  
  mpc_parser_t *mpc_startwith(mpc_parser_t *a) { return mpc_and(2, mpcf_snd, mpc_soi(), a, mpcf_dtor_null); }
  mpc_parser_t *mpc_endwith(mpc_parser_t *a, mpc_dtor_t da) { return mpc_and(2, mpcf_fst, a, mpc_eoi(), da); }
  mpc_parser_t *mpc_whole(mpc_parser_t *a, mpc_dtor_t da) { return mpc_and(3, mpcf_snd, mpc_soi(), a, mpc_eoi(), mpcf_dtor_null, da); }
  
  mpc_parser_t *mpc_stripl(mpc_parser_t *a) { return mpc_and(2, mpcf_snd, mpc_blank(), a, mpcf_dtor_null); }
  mpc_parser_t *mpc_stripr(mpc_parser_t *a) { return mpc_and(2, mpcf_fst, a, mpc_blank(), mpcf_dtor_null); }
  mpc_parser_t *mpc_strip(mpc_parser_t *a) { return mpc_and(3, mpcf_snd, mpc_blank(), a, mpc_blank(), mpcf_dtor_null, mpcf_dtor_null); }
  mpc_parser_t *mpc_tok(mpc_parser_t *a) { return mpc_and(2, mpcf_fst, a, mpc_blank(), mpcf_dtor_null); }
  mpc_parser_t *mpc_sym(const char *s) { return mpc_tok(mpc_string(s)); }
  
  mpc_parser_t *mpc_total(mpc_parser_t *a, mpc_dtor_t da) { return mpc_whole(mpc_strip(a), da); }
  
  mpc_parser_t *mpc_between(mpc_parser_t *a, mpc_dtor_t ad, const char *o, const char *c) {
    return mpc_and(3, mpcf_snd_free,
      mpc_string(o), a, mpc_string(c),
      free, ad);
  }
  
  mpc_parser_t *mpc_parens(mpc_parser_t *a, mpc_dtor_t ad)   { return mpc_between(a, ad, "(", ")"); }
  mpc_parser_t *mpc_braces(mpc_parser_t *a, mpc_dtor_t ad)   { return mpc_between(a, ad, "<", ">"); }
  mpc_parser_t *mpc_brackets(mpc_parser_t *a, mpc_dtor_t ad) { return mpc_between(a, ad, "{", "}"); }
  mpc_parser_t *mpc_squares(mpc_parser_t *a, mpc_dtor_t ad)  { return mpc_between(a, ad, "[", "]"); }
  
  mpc_parser_t *mpc_tok_between(mpc_parser_t *a, mpc_dtor_t ad, const char *o, const char *c) {
    return mpc_and(3, mpcf_snd_free,
      mpc_sym(o), mpc_tok(a), mpc_sym(c),
      free, ad);
  }
  
  mpc_parser_t *mpc_tok_parens(mpc_parser_t *a, mpc_dtor_t ad)   { return mpc_tok_between(a, ad, "(", ")"); }
  mpc_parser_t *mpc_tok_braces(mpc_parser_t *a, mpc_dtor_t ad)   { return mpc_tok_between(a, ad, "<", ">"); }
  mpc_parser_t *mpc_tok_brackets(mpc_parser_t *a, mpc_dtor_t ad) { return mpc_tok_between(a, ad, "{", "}"); }
  mpc_parser_t *mpc_tok_squares(mpc_parser_t *a, mpc_dtor_t ad)  { return mpc_tok_between(a, ad, "[", "]"); }
  
  /*
  ** Regular Expression Parsers
  */
  
  /*
  ** So here is a cute bootstrapping.
  **
  ** I'm using the previously defined
  ** mpc constructs and functions to
  ** parse the user regex string and
  ** construct a parser from it.
  **
  ** As it turns out lots of the standard
  ** mpc functions look a lot like `fold`
  ** functions and so can be used indirectly
  ** by many of the parsing functions to build
  ** a parser directly - as we are parsing.
  **
  ** This is certainly something that
  ** would be less elegant/interesting 
  ** in a two-phase parser which first
  ** builds an AST and then traverses it
  ** to generate the object.
  **
  ** This whole thing acts as a great
  ** case study for how trivial it can be
  ** to write a great parser in a few
  ** lines of code using mpc.
  */
  
  /*
  **
  **  ### Regular Expression Grammar
  **
  **      <regex> : <term> | (<term> "|" <regex>)
  **     
  **      <term> : <factor>*
  **
  **      <factor> : <base>
  **               | <base> "*"
  **               | <base> "+"
  **               | <base> "?"
  **               | <base> "{" <digits> "}"
  **           
  **      <base> : <char>
  **             | "\" <char>
  **             | "(" <regex> ")"
  **             | "[" <range> "]"
  */
  
  static mpc_val_t *mpcf_re_or(int n, mpc_val_t **xs) {
    (void) n;
    if (xs[1] == NULL) { return xs[0]; }
    else { return mpc_or(2, xs[0], xs[1]); }
  }
  
  static mpc_val_t *mpcf_re_and(int n, mpc_val_t **xs) {
    int i;
    mpc_parser_t *p = mpc_lift(mpcf_ctor_str);
    for (i = 0; i < n; i++) {
      p = mpc_and(2, mpcf_strfold, p, xs[i], free);
    }
    return p;
  }
  
  static mpc_val_t *mpcf_re_repeat(int n, mpc_val_t **xs) {
    int num;
    (void) n;
    if (xs[1] == NULL) { return xs[0]; }
    if (strcmp(xs[1], "*") == 0) { free(xs[1]); return mpc_many(mpcf_strfold, xs[0]); }
    if (strcmp(xs[1], "+") == 0) { free(xs[1]); return mpc_many1(mpcf_strfold, xs[0]); }
    if (strcmp(xs[1], "?") == 0) { free(xs[1]); return mpc_maybe_lift(xs[0], mpcf_ctor_str); }
    num = *(int*)xs[1];
    free(xs[1]);
    
    return mpc_count(num, mpcf_strfold, xs[0], free);
  }
  
  static mpc_parser_t *mpc_re_escape_char(char c) {
    switch (c) {
      case 'a': return mpc_char('\a');
      case 'f': return mpc_char('\f');
      case 'n': return mpc_char('\n');
      case 'r': return mpc_char('\r');
      case 't': return mpc_char('\t');
      case 'v': return mpc_char('\v');
      case 'b': return mpc_and(2, mpcf_snd, mpc_boundary(), mpc_lift(mpcf_ctor_str), free);
      case 'B': return mpc_not_lift(mpc_boundary(), free, mpcf_ctor_str);
      case 'A': return mpc_and(2, mpcf_snd, mpc_soi(), mpc_lift(mpcf_ctor_str), free);
      case 'Z': return mpc_and(2, mpcf_snd, mpc_eoi(), mpc_lift(mpcf_ctor_str), free);
      case 'd': return mpc_digit();
      case 'D': return mpc_not_lift(mpc_digit(), free, mpcf_ctor_str);
      case 's': return mpc_whitespace();
      case 'S': return mpc_not_lift(mpc_whitespace(), free, mpcf_ctor_str);
      case 'w': return mpc_alphanum();
      case 'W': return mpc_not_lift(mpc_alphanum(), free, mpcf_ctor_str);
      default: return NULL;
    }
  }
  
  static mpc_val_t *mpcf_re_escape(mpc_val_t *x) {
    
    char *s = x;
    mpc_parser_t *p;
    
    /* Regex Special Characters */
    if (s[0] == '.') { free(s); return mpc_any(); }
    if (s[0] == '^') { free(s); return mpc_and(2, mpcf_snd, mpc_soi(), mpc_lift(mpcf_ctor_str), free); }
    if (s[0] == '$') { free(s); return mpc_and(2, mpcf_snd, mpc_eoi(), mpc_lift(mpcf_ctor_str), free); }
    
    /* Regex Escape */
    if (s[0] == '\\') {
      p = mpc_re_escape_char(s[1]);
      p = (p == NULL) ? mpc_char(s[1]) : p;
      free(s);
      return p;
    }
    
    /* Regex Standard */
    p = mpc_char(s[0]);
    free(s);
    return p;
  }
  
  static const char *mpc_re_range_escape_char(char c) {
    switch (c) {
      case '-': return "-";
      case 'a': return "\a";
      case 'f': return "\f";
      case 'n': return "\n";
      case 'r': return "\r";
      case 't': return "\t";
      case 'v': return "\v";
      case 'b': return "\b";
      case 'd': return "0123456789";
      case 's': return " \f\n\r\t\v";
      case 'w': return "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_";
      default: return NULL;
    }
  }
  
  static mpc_val_t *mpcf_re_range(mpc_val_t *x) {
    
    mpc_parser_t *out;
    size_t i, j;
    size_t start, end;
    const char *tmp = NULL;
    const char *s = x;
    int comp = s[0] == '^' ? 1 : 0;
    char *range = calloc(1,1);
    
    if (s[0] == '\0') { free(x); return mpc_fail("Invalid Regex Range Expression"); } 
    if (s[0] == '^' && 
        s[1] == '\0') { free(x); return mpc_fail("Invalid Regex Range Expression"); }
    
    for (i = comp; i < strlen(s); i++){
      
      /* Regex Range Escape */
      if (s[i] == '\\') {
        tmp = mpc_re_range_escape_char(s[i+1]);
        if (tmp != NULL) {
          range = reallocate(range, strlen(range) + strlen(tmp) + 1);
          strcat(range, tmp);
        } else {
          range = reallocate(range, strlen(range) + 1 + 1);
          range[strlen(range) + 1] = '\0';
          range[strlen(range) + 0] = s[i+1];      
        }
        i++;
      }
      
      /* Regex Range...Range */
      else if (s[i] == '-') {
        if (s[i+1] == '\0' || i == 0) {
            range = reallocate(range, strlen(range) + strlen("-") + 1);
            strcat(range, "-");
        } else {
          start = s[i-1]+1;
          end = s[i+1]-1;
          for (j = start; j <= end; j++) {
            range = reallocate(range, strlen(range) + 1 + 1 + 1);
            range[strlen(range) + 1] = '\0';
            range[strlen(range) + 0] = (char)j;
          }        
        }
      }
      
      /* Regex Range Normal */
      else {
        range = reallocate(range, strlen(range) + 1 + 1);
        range[strlen(range) + 1] = '\0';
        range[strlen(range) + 0] = s[i];
      }
    
    }
    
    out = comp == 1 ? mpc_noneof(range) : mpc_oneof(range);
    
    free(x);
    free(range);
    
    return out;
  }
  
  mpc_parser_t *mpc_re(const char *re) {
    
    char *err_msg;
    mpc_parser_t *err_out;
    mpc_result_t r;
    mpc_parser_t *Regex, *Term, *Factor, *Base, *Range, *RegexEnclose; 
    
    Regex  = mpc_new("regex");
    Term   = mpc_new("term");
    Factor = mpc_new("factor");
    Base   = mpc_new("base");
    Range  = mpc_new("range");
    
    mpc_define(Regex, mpc_and(2, mpcf_re_or,
      Term, 
      mpc_maybe(mpc_and(2, mpcf_snd_free, mpc_char('|'), Regex, free)),
      (mpc_dtor_t)mpc_delete
    ));
    
    mpc_define(Term, mpc_many(mpcf_re_and, Factor));
    
    mpc_define(Factor, mpc_and(2, mpcf_re_repeat,
      Base,
      mpc_or(5,
        mpc_char('*'), mpc_char('+'), mpc_char('?'),
        mpc_brackets(mpc_int(), free),
        mpc_pass()),
      (mpc_dtor_t)mpc_delete
    ));
    
    mpc_define(Base, mpc_or(4,
      mpc_parens(Regex, (mpc_dtor_t)mpc_delete),
      mpc_squares(Range, (mpc_dtor_t)mpc_delete),
      mpc_apply(mpc_escape(), mpcf_re_escape),
      mpc_apply(mpc_noneof(")|"), mpcf_re_escape)
    ));
    
    mpc_define(Range, mpc_apply(
      mpc_many(mpcf_strfold, mpc_or(2, mpc_escape(), mpc_noneof("]"))),
      mpcf_re_range
    ));
    
    RegexEnclose = mpc_whole(mpc_predictive(Regex), (mpc_dtor_t)mpc_delete);
    
    mpc_optimise(RegexEnclose);
    mpc_optimise(Regex);
    mpc_optimise(Term);
    mpc_optimise(Factor);
    mpc_optimise(Base);
    mpc_optimise(Range);
    
    if(!mpc_parse("<mpc_re_compiler>", re, RegexEnclose, &r)) {
      err_msg = mpc_err_string(r.error);
      err_out = mpc_failf("Invalid Regex: %s", err_msg);
      mpc_err_delete(r.error);  
      free(err_msg);
      r.output = err_out;
    }
    
    mpc_cleanup(6, RegexEnclose, Regex, Term, Factor, Base, Range);
    
    mpc_optimise(r.output);
    
    return r.output;
    
  }
  
  /*
  ** Common Fold Functions
  */
  
  void mpcf_dtor_null(mpc_val_t *x) { (void) x; return; }
  
  mpc_val_t *mpcf_ctor_null(void) { return NULL; }
  mpc_val_t *mpcf_ctor_str(void) { return calloc(1, 1); }
  mpc_val_t *mpcf_free(mpc_val_t *x) { free(x); return NULL; }
  
  mpc_val_t *mpcf_int(mpc_val_t *x) {
    int *y = allocate(sizeof(int));
    *y = strtol(x, NULL, 10);
    free(x);
    return y;
  }
  
  mpc_val_t *mpcf_hex(mpc_val_t *x) {
    int *y = allocate(sizeof(int));
    *y = strtol(x, NULL, 16);
    free(x);
    return y;
  }
  
  mpc_val_t *mpcf_oct(mpc_val_t *x) {
    int *y = allocate(sizeof(int));
    *y = strtol(x, NULL, 8);
    free(x);
    return y;
  }
  
  mpc_val_t *mpcf_float(mpc_val_t *x) {
    float *y = allocate(sizeof(float));
    *y = strtof(x, NULL);
    free(x);
    return y;
  }
  
  mpc_val_t *mpcf_strtriml(mpc_val_t *x) {
    char *s = x;
    while (isspace(*s)) {
      memmove(s, s+1, strlen(s));
    }
    return s;
  }
  
  mpc_val_t *mpcf_strtrimr(mpc_val_t *x) {
    char *s = x;
    size_t l = strlen(s);
    while (isspace(s[l-1])) {
      s[l-1] = '\0'; l--;
    }
    return s;
  }
  
  mpc_val_t *mpcf_strtrim(mpc_val_t *x) {
    return mpcf_strtriml(mpcf_strtrimr(x));
  }
  
  static const char mpc_escape_input_c[]  = {
    '\a', '\b', '\f', '\n', '\r',
    '\t', '\v', '\\', '\'', '\"', '\0'};
      
  static const char *mpc_escape_output_c[] = {
    "\\a", "\\b", "\\f", "\\n", "\\r", "\\t", 
    "\\v", "\\\\", "\\'", "\\\"", "\\0", NULL};
  
  static const char mpc_escape_input_raw_re[] = { '/' };
  static const char *mpc_escape_output_raw_re[] = { "\\/", NULL };
  
  static const char mpc_escape_input_raw_cstr[] = { '"' };
  static const char *mpc_escape_output_raw_cstr[] = { "\\\"", NULL };
  
  static const char mpc_escape_input_raw_cchar[] = { '\'' };
  static const char *mpc_escape_output_raw_cchar[] = { "\\'", NULL };
  
  static mpc_val_t *mpcf_escape_new(mpc_val_t *x, const char *input, const char **output) {
    
    int i;
    int found;
    char buff[2];
    char *s = x;
    char *y = calloc(1, 1);
    
    while (*s) {
      
      i = 0;
      found = 0;
  
      while (output[i]) {
        if (*s == input[i]) {
          y = reallocate(y, strlen(y) + strlen(output[i]) + 1);
          strcat(y, output[i]);
          found = 1;
          break;
        }
        i++;
      }
      
      if (!found) {
        y = reallocate(y, strlen(y) + 2);
        buff[0] = *s; buff[1] = '\0';
        strcat(y, buff);
      }
      
      s++;
    }
    
    
    return y;
  }
  
  static mpc_val_t *mpcf_unescape_new(mpc_val_t *x, const char *input, const char **output) {
    
    int i;
    int found = 0;
    char buff[2];
    char *s = x;
    char *y = calloc(1, 1);
    
    while (*s) {
      
      i = 0;
      found = 0;
      
      while (output[i]) {
        if ((*(s+0)) == output[i][0] &&
            (*(s+1)) == output[i][1]) {
          y = reallocate(y, strlen(y) + 1 + 1);
          buff[0] = input[i]; buff[1] = '\0';
          strcat(y, buff);
          found = 1;
          s++;
          break;
        }
        i++;
      }
      
      if (!found) {
        y = reallocate(y, strlen(y) + 1 + 1);
        buff[0] = *s; buff[1] = '\0';
        strcat(y, buff);
      }
      
      if (*s == '\0') { break; }
      else { s++; }
    }
    
    return y;
    
  }
  
  mpc_val_t *mpcf_escape(mpc_val_t *x) {
    mpc_val_t *y = mpcf_escape_new(x, mpc_escape_input_c, mpc_escape_output_c);
    free(x);
    return y;
  }
  
  mpc_val_t *mpcf_unescape(mpc_val_t *x) {
    mpc_val_t *y = mpcf_unescape_new(x, mpc_escape_input_c, mpc_escape_output_c);
    free(x);
    return y;
  }
  
  mpc_val_t *mpcf_escape_regex(mpc_val_t *x) {
    mpc_val_t *y = mpcf_escape_new(x, mpc_escape_input_raw_re, mpc_escape_output_raw_re);
    free(x);
    return y;  
  }
  
  mpc_val_t *mpcf_unescape_regex(mpc_val_t *x) {
    mpc_val_t *y = mpcf_unescape_new(x, mpc_escape_input_raw_re, mpc_escape_output_raw_re);
    free(x);
    return y;  
  }
  
  mpc_val_t *mpcf_escape_string_raw(mpc_val_t *x) {
    mpc_val_t *y = mpcf_escape_new(x, mpc_escape_input_raw_cstr, mpc_escape_output_raw_cstr);
    free(x);
    return y;
  }
  
  mpc_val_t *mpcf_unescape_string_raw(mpc_val_t *x) {
    mpc_val_t *y = mpcf_unescape_new(x, mpc_escape_input_raw_cstr, mpc_escape_output_raw_cstr);
    free(x);
    return y;
  }
  
  mpc_val_t *mpcf_escape_char_raw(mpc_val_t *x) {
    mpc_val_t *y = mpcf_escape_new(x, mpc_escape_input_raw_cchar, mpc_escape_output_raw_cchar);
    free(x);
    return y;
  }
  
  mpc_val_t *mpcf_unescape_char_raw(mpc_val_t *x) {
    mpc_val_t *y = mpcf_unescape_new(x, mpc_escape_input_raw_cchar, mpc_escape_output_raw_cchar);
    free(x);
    return y;
  }
  
  mpc_val_t *mpcf_null(int n, mpc_val_t** xs) { (void) n; (void) xs; return NULL; }
  mpc_val_t *mpcf_fst(int n, mpc_val_t **xs) { (void) n; return xs[0]; }
  mpc_val_t *mpcf_snd(int n, mpc_val_t **xs) { (void) n; return xs[1]; }
  mpc_val_t *mpcf_trd(int n, mpc_val_t **xs) { (void) n; return xs[2]; }
  
  static mpc_val_t *mpcf_nth_free(int n, mpc_val_t **xs, int x) {
    int i;
    for (i = 0; i < n; i++) {
      if (i != x) { free(xs[i]); }
    }
    return xs[x];
  }
   
  mpc_val_t *mpcf_fst_free(int n, mpc_val_t **xs) { return mpcf_nth_free(n, xs, 0); }
  mpc_val_t *mpcf_snd_free(int n, mpc_val_t **xs) { return mpcf_nth_free(n, xs, 1); }
  mpc_val_t *mpcf_trd_free(int n, mpc_val_t **xs) { return mpcf_nth_free(n, xs, 2); }
  
  mpc_val_t *mpcf_strfold(int n, mpc_val_t **xs) {
    int i;
    size_t l = 0;
    
    if (n == 0) { return calloc(1, 1); }
    
    for (i = 0; i < n; i++) { l += strlen(xs[i]); }
    
    xs[0] = reallocate(xs[0], l + 1);
    
    for (i = 1; i < n; i++) {
      strcat(xs[0], xs[i]); free(xs[i]);
    }
    
    return xs[0];
  }
  
  mpc_val_t *mpcf_maths(int n, mpc_val_t **xs) {
    int **vs = (int**)xs;
    (void) n;
    
    if (strcmp(xs[1], "*") == 0) { *vs[0] *= *vs[2]; }
    if (strcmp(xs[1], "/") == 0) { *vs[0] /= *vs[2]; }
    if (strcmp(xs[1], "%") == 0) { *vs[0] %= *vs[2]; }
    if (strcmp(xs[1], "+") == 0) { *vs[0] += *vs[2]; }
    if (strcmp(xs[1], "-") == 0) { *vs[0] -= *vs[2]; }
    
    free(xs[1]); free(xs[2]);
    
    return xs[0];
  }
  
  /*
  ** Printing
  */
  
  static void mpc_print_unretained(mpc_parser_t *p, int force) {
    
    /* TODO: Print Everything Escaped */
    
    int i;
    char *s, *e;
    char buff[2];
    
    if (p->retained && !force) {;
      if (p->name) { printf("<%s>", p->name); }
      else { printf("<anon>"); }
      return;
    }
    
    if (p->type == MPC_TYPE_UNDEFINED) { printf("<?>"); }
    if (p->type == MPC_TYPE_PASS)   { printf("<:>"); }
    if (p->type == MPC_TYPE_FAIL)   { printf("<!>"); }
    if (p->type == MPC_TYPE_LIFT)   { printf("<#>"); }
    if (p->type == MPC_TYPE_STATE)  { printf("<S>"); }
    if (p->type == MPC_TYPE_ANCHOR) { printf("<@>"); }
    if (p->type == MPC_TYPE_EXPECT) {
      printf("%s", p->data.expect.m);
      /*mpc_print_unretained(p->data.expect.x, 0);*/
    }
    
    if (p->type == MPC_TYPE_ANY) { printf("<.>"); }
    if (p->type == MPC_TYPE_SATISFY) { printf("<f>"); }
  
    if (p->type == MPC_TYPE_SINGLE) {
      buff[0] = p->data.single.x; buff[1] = '\0';
      s = mpcf_escape_new(
        buff,
        mpc_escape_input_c,
        mpc_escape_output_c);
      printf("'%s'", s);
      free(s);
    }
    
    if (p->type == MPC_TYPE_RANGE) {
      buff[0] = p->data.range.x; buff[1] = '\0';
      s = mpcf_escape_new(
        buff,
        mpc_escape_input_c,
        mpc_escape_output_c);
      buff[0] = p->data.range.y; buff[1] = '\0';
      e = mpcf_escape_new(
        buff,
        mpc_escape_input_c,
        mpc_escape_output_c);
      printf("[%s-%s]", s, e);
      free(s);
      free(e);
    }
    
    if (p->type == MPC_TYPE_ONEOF) {
      s = mpcf_escape_new(
        p->data.string.x,
        mpc_escape_input_c,
        mpc_escape_output_c);
      printf("[%s]", s);
      free(s);
    }
    
    if (p->type == MPC_TYPE_NONEOF) {
      s = mpcf_escape_new(
        p->data.string.x,
        mpc_escape_input_c,
        mpc_escape_output_c);
      printf("[^%s]", s);
      free(s);
    }
    
    if (p->type == MPC_TYPE_STRING) {
      s = mpcf_escape_new(
        p->data.string.x,
        mpc_escape_input_c,
        mpc_escape_output_c);
      printf("\"%s\"", s);
      free(s);
    }
    
    if (p->type == MPC_TYPE_APPLY)    { mpc_print_unretained(p->data.apply.x, 0); }
    if (p->type == MPC_TYPE_APPLY_TO) { mpc_print_unretained(p->data.apply_to.x, 0); }
    if (p->type == MPC_TYPE_PREDICT)  { mpc_print_unretained(p->data.predict.x, 0); }
  
    if (p->type == MPC_TYPE_NOT)   { mpc_print_unretained(p->data.not.x, 0); printf("!"); }
    if (p->type == MPC_TYPE_MAYBE) { mpc_print_unretained(p->data.not.x, 0); printf("?"); }
  
    if (p->type == MPC_TYPE_MANY)  { mpc_print_unretained(p->data.repeat.x, 0); printf("*"); }
    if (p->type == MPC_TYPE_MANY1) { mpc_print_unretained(p->data.repeat.x, 0); printf("+"); }
    if (p->type == MPC_TYPE_COUNT) { mpc_print_unretained(p->data.repeat.x, 0); printf("{%i}", p->data.repeat.n); }
    
    if (p->type == MPC_TYPE_OR) {
      printf("(");
      for(i = 0; i < p->data.or.n-1; i++) {
        mpc_print_unretained(p->data.or.xs[i], 0);
        printf(" | ");
      }
      mpc_print_unretained(p->data.or.xs[p->data.or.n-1], 0);
      printf(")");
    }
    
    if (p->type == MPC_TYPE_AND) {
      printf("(");
      for(i = 0; i < p->data.and.n-1; i++) {
        mpc_print_unretained(p->data.and.xs[i], 0);
        printf(" ");
      }
      mpc_print_unretained(p->data.and.xs[p->data.and.n-1], 0);
      printf(")");
    }
    
  }
  
  void mpc_print(mpc_parser_t *p) {
    mpc_print_unretained(p, 1);
    printf("\n");
  }
  
  /*
  ** Testing
  */
  
  /*
  ** These functions are slightly unwieldy and
  ** also the whole of the testing suite for mpc
  ** mpc is pretty shaky.
  **
  ** It could do with a lot more tests and more
  ** precision. Currently I am only really testing
  ** changes off of the examples.
  **
  */
  
  int mpc_test_fail(mpc_parser_t *p, const char *s, const void *d,
    int(*tester)(const void*, const void*),
    mpc_dtor_t destructor,
    void(*printer)(const void*)) {
    mpc_result_t r;
    (void) printer;
    if (mpc_parse("<test>", s, p, &r)) {
  
      if (tester(r.output, d)) {
        destructor(r.output);
        return 0;
      } else {
        destructor(r.output);
        return 1;
      }
    
    } else {
      mpc_err_delete(r.error);
      return 1;
    }
    
  }
  
  int mpc_test_pass(mpc_parser_t *p, const char *s, const void *d,
    int(*tester)(const void*, const void*), 
    mpc_dtor_t destructor, 
    void(*printer)(const void*)) {
  
    mpc_result_t r;  
    if (mpc_parse("<test>", s, p, &r)) {
      
      if (tester(r.output, d)) {
        destructor(r.output);
        return 1;
      } else {
        printf("Got "); printer(r.output); printf("\n");
        printf("Expected "); printer(d); printf("\n");
        destructor(r.output);
        return 0;
      }
      
    } else {    
      mpc_err_print(r.error);
      mpc_err_delete(r.error);
      return 0;
      
    }
    
  }
  
  
  /*
  ** AST
  */
  
  void mpc_ast_delete(mpc_ast_t *a) {
    
    int i;
    
    if (a == NULL) { return; }
    
    for (i = 0; i < a->children_num; i++) {
      mpc_ast_delete(a->children[i]);
    }
    
    free(a->children);
    free(a->tag);
    free(a->contents);
    free(a);
    
  }
  
  static void mpc_ast_delete_no_children(mpc_ast_t *a) {
    free(a->children);
    free(a->tag);
    free(a->contents);
    free(a);
  }
  
  mpc_ast_t *mpc_ast_new(const char *tag, const char *contents) {
    
    mpc_ast_t *a = allocate(sizeof(mpc_ast_t));
    
    a->tag = allocate(strlen(tag) + 1);
    strcpy(a->tag, tag);
    
    a->contents = allocate(strlen(contents) + 1);
    strcpy(a->contents, contents);
    
    a->state = mpc_state_new();
    
    a->children_num = 0;
    a->children = NULL;
    return a;
    
  }
  
  mpc_ast_t *mpc_ast_build(int n, const char *tag, ...) {
    
    mpc_ast_t *a = mpc_ast_new(tag, "");
    
    int i;
    va_list va;
    va_start(va, tag);
    
    for (i = 0; i < n; i++) {
      mpc_ast_add_child(a, va_arg(va, mpc_ast_t*));
    }
    
    va_end(va);
    
    return a;
    
  }
  
  mpc_ast_t *mpc_ast_add_root(mpc_ast_t *a) {
  
    mpc_ast_t *r;
  
    if (a == NULL) { return a; }
    if (a->children_num == 0) { return a; }
    if (a->children_num == 1) { return a; }
  
    r = mpc_ast_new(">", "");
    mpc_ast_add_child(r, a);
    return r;
  }
  
  int mpc_ast_eq(mpc_ast_t *a, mpc_ast_t *b) {
    
    int i;
  
    if (strcmp(a->tag, b->tag) != 0) { return 0; }
    if (strcmp(a->contents, b->contents) != 0) { return 0; }
    if (a->children_num != b->children_num) { return 0; }
    
    for (i = 0; i < a->children_num; i++) {
      if (!mpc_ast_eq(a->children[i], b->children[i])) { return 0; }
    }
    
    return 1;
  }
  
  mpc_ast_t *mpc_ast_add_child(mpc_ast_t *r, mpc_ast_t *a) {
    r->children_num++;
    r->children = reallocate(r->children, sizeof(mpc_ast_t*) * r->children_num);
    r->children[r->children_num-1] = a;
    return r;
  }
  
  mpc_ast_t *mpc_ast_add_tag(mpc_ast_t *a, const char *t) {
    if (a == NULL) { return a; }
    a->tag = reallocate(a->tag, strlen(t) + 1 + strlen(a->tag) + 1);
    memmove(a->tag + strlen(t) + 1, a->tag, strlen(a->tag)+1);
    memmove(a->tag, t, strlen(t));
    memmove(a->tag + strlen(t), "|", 1);
    return a;
  }
  
  mpc_ast_t *mpc_ast_add_root_tag(mpc_ast_t *a, const char *t) {
    if (a == NULL) { return a; }
    a->tag = reallocate(a->tag, (strlen(t)-1) + strlen(a->tag) + 1);
    memmove(a->tag + (strlen(t)-1), a->tag, strlen(a->tag)+1);
    memmove(a->tag, t, (strlen(t)-1));
    return a;
  }
  
  mpc_ast_t *mpc_ast_tag(mpc_ast_t *a, const char *t) {
    a->tag = reallocate(a->tag, strlen(t) + 1);
    strcpy(a->tag, t);
    return a;
  }
  
  mpc_ast_t *mpc_ast_state(mpc_ast_t *a, mpc_state_t s) {
    if (a == NULL) { return a; }
    a->state = s;
    return a;
  }
  
  static void mpc_ast_print_depth(mpc_ast_t *a, int d, FILE *fp) {
    
    int i;
    
    if (a == NULL) {
      fprintf(fp, "NULL\n");
      return;
    }
    
    for (i = 0; i < d; i++) { fprintf(fp, "  "); }
    
    if (strlen(a->contents)) {
      fprintf(fp, "%s:%lu:%lu '%s'\n", a->tag, 
        (long unsigned int)(a->state.row+1),
        (long unsigned int)(a->state.col+1),
        a->contents);
    } else {
      fprintf(fp, "%s \n", a->tag);
    }
    
    for (i = 0; i < a->children_num; i++) {
      mpc_ast_print_depth(a->children[i], d+1, fp);
    }
    
  }
  
  void mpc_ast_print(mpc_ast_t *a) {
    mpc_ast_print_depth(a, 0, stdout);
  }
  
  void mpc_ast_print_to(mpc_ast_t *a, FILE *fp) {
    mpc_ast_print_depth(a, 0, fp);
  }
  
  int mpc_ast_get_index(mpc_ast_t *ast, const char *tag) {
    return mpc_ast_get_index_lb(ast, tag, 0);
  }
  
  int mpc_ast_get_index_lb(mpc_ast_t *ast, const char *tag, int lb) {
    int i;
  
    for(i=lb; i<ast->children_num; i++) {
      if(strcmp(ast->children[i]->tag, tag) == 0) {
        return i;
      }
    }
  
    return -1;
  }
  
  mpc_ast_t *mpc_ast_get_child(mpc_ast_t *ast, const char *tag) {
    return mpc_ast_get_child_lb(ast, tag, 0);
  }
  
  mpc_ast_t *mpc_ast_get_child_lb(mpc_ast_t *ast, const char *tag, int lb) {
    int i;
  
    for(i=lb; i<ast->children_num; i++) {
      if(strcmp(ast->children[i]->tag, tag) == 0) {
        return ast->children[i];
      }
    }
  
    return NULL;
  }
  
  mpc_ast_trav_t *mpc_ast_traverse_start(mpc_ast_t *ast,
                                         mpc_ast_trav_order_t order)
  {
    mpc_ast_trav_t *trav, *n_trav;
    mpc_ast_t *cnode = ast;
  
    /* Create the traversal structure */
    trav = allocate(sizeof(mpc_ast_trav_t));
    trav->curr_node = cnode;
    trav->parent = NULL;
    trav->curr_child = 0;
    trav->order = order;
  
    /* Get start node */
    switch(order) {
      case mpc_ast_trav_order_pre:
        /* Nothing else is needed for pre order start */
        break;
  
      case mpc_ast_trav_order_post:
        while(cnode->children_num > 0) {
          cnode = cnode->children[0];
  
          n_trav = allocate(sizeof(mpc_ast_trav_t));
          n_trav->curr_node = cnode;
          n_trav->parent = trav;
          n_trav->curr_child = 0;
          n_trav->order = order;
  
          trav = n_trav;
        }
  
        break;
  
      default:
        /* Unreachable, but compiler complaints */
        break;
    }
  
    return trav;
  }
  
  mpc_ast_t *mpc_ast_traverse_next(mpc_ast_trav_t **trav) {
    mpc_ast_trav_t *n_trav, *to_free;
    mpc_ast_t *ret = NULL;
    int cchild;
  
    /* The end of traversal was reached */
    if(*trav == NULL) return NULL;
  
    switch((*trav)->order) {
      case mpc_ast_trav_order_pre:
        ret = (*trav)->curr_node;
  
        /* If there aren't any more children, go up */
        while(*trav != NULL &&
          (*trav)->curr_child >= (*trav)->curr_node->children_num)
        {
          to_free = *trav;
          *trav = (*trav)->parent;
          free(to_free);
        }
  
        /* If trav is NULL, the end was reached */
        if(*trav == NULL) {
          break;
        }
  
        /* Go to next child */
        n_trav = allocate(sizeof(mpc_ast_trav_t));
  
        cchild = (*trav)->curr_child;
        n_trav->curr_node = (*trav)->curr_node->children[cchild];
        n_trav->parent = *trav;
        n_trav->curr_child = 0;
        n_trav->order = (*trav)->order;
  
        (*trav)->curr_child++;
        *trav = n_trav;
  
        break;
  
      case mpc_ast_trav_order_post:
        ret = (*trav)->curr_node;
  
        /* Move up tree to the parent If the parent doesn't have any more nodes,
         * then this is the current node. If it does, move down to its left most
         * child. Also, free the previous traversal node */
        to_free = *trav;
        *trav = (*trav)->parent;
        free(to_free);
  
        if(*trav == NULL)
          break;
  
        /* Next child */
        (*trav)->curr_child++;
  
        /* If there aren't any more children, this is the next node */
        if((*trav)->curr_child >= (*trav)->curr_node->children_num) {
          break;
        }
  
        /* If there are still more children, find the leftmost child from this
         * node */
        while((*trav)->curr_node->children_num > 0) {
          n_trav = allocate(sizeof(mpc_ast_trav_t));
  
          cchild = (*trav)->curr_child;
          n_trav->curr_node = (*trav)->curr_node->children[cchild];
          n_trav->parent = *trav;
          n_trav->curr_child = 0;
          n_trav->order = (*trav)->order;
  
          *trav = n_trav;
        }
  
      default:
        /* Unreachable, but compiler complaints */
        break;
    }
  
    return ret;
  }
  
  void mpc_ast_traverse_free(mpc_ast_trav_t **trav) {
    mpc_ast_trav_t *n_trav;
  
    /* Go through parents until all are free */
    while(*trav != NULL) {
        n_trav = (*trav)->parent;
        free(*trav);
        *trav = n_trav;
    }
  }
  
  mpc_val_t *mpcf_fold_ast(int n, mpc_val_t **xs) {
    
    int i, j;
    mpc_ast_t** as = (mpc_ast_t**)xs;
    mpc_ast_t *r;
    
    if (n == 0) { return NULL; }
    if (n == 1) { return xs[0]; }
    if (n == 2 && xs[1] == NULL) { return xs[0]; }
    if (n == 2 && xs[0] == NULL) { return xs[1]; }
    
    r = mpc_ast_new(">", "");
    
    for (i = 0; i < n; i++) {
      
      if (as[i] == NULL) { continue; }
      
      if        (as[i] && as[i]->children_num == 0) {
        mpc_ast_add_child(r, as[i]);
      } else if (as[i] && as[i]->children_num == 1) {
        mpc_ast_add_child(r, mpc_ast_add_root_tag(as[i]->children[0], as[i]->tag));
        mpc_ast_delete_no_children(as[i]);
      } else if (as[i] && as[i]->children_num >= 2) {
        for (j = 0; j < as[i]->children_num; j++) {
          mpc_ast_add_child(r, as[i]->children[j]);
        }
        mpc_ast_delete_no_children(as[i]);
      }
    
    }
    
    if (r->children_num) {
      r->state = r->children[0]->state;
    }
    
    return r;
  }
  
  mpc_val_t *mpcf_str_ast(mpc_val_t *c) {
    mpc_ast_t *a = mpc_ast_new("", c);
    free(c);
    return a;
  }
  
  mpc_val_t *mpcf_state_ast(int n, mpc_val_t **xs) {
    mpc_state_t *s = ((mpc_state_t**)xs)[0];
    mpc_ast_t *a = ((mpc_ast_t**)xs)[1];
    (void)n;
    a = mpc_ast_state(a, *s);
    free(s);
    return a;
  }
  
  mpc_parser_t *mpca_state(mpc_parser_t *a) {
    return mpc_and(2, mpcf_state_ast, mpc_state(), a, free);
  }
  
  mpc_parser_t *mpca_tag(mpc_parser_t *a, const char *t) {
    return mpc_apply_to(a, (mpc_apply_to_t)mpc_ast_tag, (void*)t);
  }
  
  mpc_parser_t *mpca_add_tag(mpc_parser_t *a, const char *t) {
    return mpc_apply_to(a, (mpc_apply_to_t)mpc_ast_add_tag, (void*)t);
  }
  
  mpc_parser_t *mpca_root(mpc_parser_t *a) {
    return mpc_apply(a, (mpc_apply_t)mpc_ast_add_root);
  }
  
  mpc_parser_t *mpca_not(mpc_parser_t *a) { return mpc_not(a, (mpc_dtor_t)mpc_ast_delete); }
  mpc_parser_t *mpca_maybe(mpc_parser_t *a) { return mpc_maybe(a); }
  mpc_parser_t *mpca_many(mpc_parser_t *a) { return mpc_many(mpcf_fold_ast, a); }
  mpc_parser_t *mpca_many1(mpc_parser_t *a) { return mpc_many1(mpcf_fold_ast, a); }
  mpc_parser_t *mpca_count(int n, mpc_parser_t *a) { return mpc_count(n, mpcf_fold_ast, a, (mpc_dtor_t)mpc_ast_delete); }
  
  mpc_parser_t *mpca_or(int n, ...) {
  
    int i;
    va_list va;
  
    mpc_parser_t *p = mpc_undefined();
    
    p->type = MPC_TYPE_OR;
    p->data.or.n = n;
    p->data.or.xs = allocate(sizeof(mpc_parser_t*) * n);
    
    va_start(va, n);  
    for (i = 0; i < n; i++) {
      p->data.or.xs[i] = va_arg(va, mpc_parser_t*);
    }
    va_end(va);
    
    return p;
    
  }
  
  mpc_parser_t *mpca_and(int n, ...) {
    
    int i;
    va_list va;
    
    mpc_parser_t *p = mpc_undefined();
    
    p->type = MPC_TYPE_AND;
    p->data.and.n = n;
    p->data.and.f = mpcf_fold_ast;
    p->data.and.xs = allocate(sizeof(mpc_parser_t*) * n);
    p->data.and.dxs = allocate(sizeof(mpc_dtor_t) * (n-1));
    
    va_start(va, n);
    for (i = 0; i < n; i++) {
      p->data.and.xs[i] = va_arg(va, mpc_parser_t*);
    }
    for (i = 0; i < (n-1); i++) {
      p->data.and.dxs[i] = (mpc_dtor_t)mpc_ast_delete;
    }    
    va_end(va);
    
    return p;  
  }
  
  mpc_parser_t *mpca_total(mpc_parser_t *a) { return mpc_total(a, (mpc_dtor_t)mpc_ast_delete); }
  
  /*
  ** Grammar Parser
  */
  
  /*
  ** This is another interesting bootstrapping.
  **
  ** Having a general purpose AST type allows
  ** users to specify the grammar alone and
  ** let all fold rules be automatically taken
  ** care of by existing functions.
  **
  ** You don't get to control the type spat
  ** out but this means you can make a nice
  ** parser to take in some grammar in nice
  ** syntax and spit out a parser that works.
  **
  ** The grammar for this looks surprisingly
  ** like regex but the main difference is that
  ** it is now whitespace insensitive and the
  ** base type takes literals of some form.
  */
  
  /*
  **
  **  ### Grammar Grammar
  **
  **      <grammar> : (<term> "|" <grammar>) | <term>
  **     
  **      <term> : <factor>*
  **
  **      <factor> : <base>
  **               | <base> "*"
  **               | <base> "+"
  **               | <base> "?"
  **               | <base> "{" <digits> "}"
  **           
  **      <base> : "<" (<digits> | <ident>) ">"
  **             | <string_lit>
  **             | <char_lit>
  **             | <regex_lit>
  **             | "(" <grammar> ")"
  */
  
  typedef struct {
    va_list *va;
    int parsers_num;
    mpc_parser_t **parsers;
    int flags;
  } mpca_grammar_st_t;
  
  static mpc_val_t *mpcaf_grammar_or(int n, mpc_val_t **xs) {
    (void) n;
    if (xs[1] == NULL) { return xs[0]; }
    else { return mpca_or(2, xs[0], xs[1]); }
  }
  
  static mpc_val_t *mpcaf_grammar_and(int n, mpc_val_t **xs) {
    int i;
    mpc_parser_t *p = mpc_pass();  
    for (i = 0; i < n; i++) {
      if (xs[i] != NULL) { p = mpca_and(2, p, xs[i]); }
    }
    return p;
  }
  
  static mpc_val_t *mpcaf_grammar_repeat(int n, mpc_val_t **xs) { 
    int num;
    (void) n;
    if (xs[1] == NULL) { return xs[0]; }  
    if (strcmp(xs[1], "*") == 0) { free(xs[1]); return mpca_many(xs[0]); }
    if (strcmp(xs[1], "+") == 0) { free(xs[1]); return mpca_many1(xs[0]); }
    if (strcmp(xs[1], "?") == 0) { free(xs[1]); return mpca_maybe(xs[0]); }
    if (strcmp(xs[1], "!") == 0) { free(xs[1]); return mpca_not(xs[0]); }
    num = *((int*)xs[1]);
    free(xs[1]);
    return mpca_count(num, xs[0]);
  }
  
  static mpc_val_t *mpcaf_grammar_string(mpc_val_t *x, void *s) {
    mpca_grammar_st_t *st = s;
    char *y = mpcf_unescape(x);
    mpc_parser_t *p = (st->flags & MPCA_LANG_WHITESPACE_SENSITIVE) ? mpc_string(y) : mpc_tok(mpc_string(y));
    free(y);
    return mpca_state(mpca_tag(mpc_apply(p, mpcf_str_ast), "string"));
  }
  
  static mpc_val_t *mpcaf_grammar_char(mpc_val_t *x, void *s) {
    mpca_grammar_st_t *st = s;
    char *y = mpcf_unescape(x);
    mpc_parser_t *p = (st->flags & MPCA_LANG_WHITESPACE_SENSITIVE) ? mpc_char(y[0]) : mpc_tok(mpc_char(y[0]));
    free(y);
    return mpca_state(mpca_tag(mpc_apply(p, mpcf_str_ast), "char"));
  }
  
  static mpc_val_t *mpcaf_grammar_regex(mpc_val_t *x, void *s) {
    mpca_grammar_st_t *st = s;
    char *y = mpcf_unescape_regex(x);
    mpc_parser_t *p = (st->flags & MPCA_LANG_WHITESPACE_SENSITIVE) ? mpc_re(y) : mpc_tok(mpc_re(y));
    free(y);
    return mpca_state(mpca_tag(mpc_apply(p, mpcf_str_ast), "regex"));
  }
  
  /* Should this just use `isdigit` instead? */
  static int is_number(const char* s) {
    size_t i;
    for (i = 0; i < strlen(s); i++) { if (!strchr("0123456789", s[i])) { return 0; } }
    return 1;
  }
  
  static mpc_parser_t *mpca_grammar_find_parser(char *x, mpca_grammar_st_t *st) {
    
    int i;
    mpc_parser_t *p;
    
    /* Case of Number */
    if (is_number(x)) {
  
      i = strtol(x, NULL, 10);
      
      while (st->parsers_num <= i) {
        st->parsers_num++;
        st->parsers = reallocate(st->parsers, sizeof(mpc_parser_t*) * st->parsers_num);
        st->parsers[st->parsers_num-1] = va_arg(*st->va, mpc_parser_t*);
        if (st->parsers[st->parsers_num-1] == NULL) {
          return mpc_failf("No Parser in position %i! Only supplied %i Parsers!", i, st->parsers_num);
        }
      }
      
      return st->parsers[st->parsers_num-1];
    
    /* Case of Identifier */
    } else {
      
      /* Search Existing Parsers */
      for (i = 0; i < st->parsers_num; i++) {
        mpc_parser_t *q = st->parsers[i];
        if (q == NULL) { return mpc_failf("Unknown Parser '%s'!", x); }
        if (q->name && strcmp(q->name, x) == 0) { return q; }
      }
      
      /* Search New Parsers */
      while (1) {
      
        p = va_arg(*st->va, mpc_parser_t*);
        
        st->parsers_num++;
        st->parsers = reallocate(st->parsers, sizeof(mpc_parser_t*) * st->parsers_num);
        st->parsers[st->parsers_num-1] = p;
        
        if (p == NULL) { return mpc_failf("Unknown Parser '%s'!", x); }
        if (p->name && strcmp(p->name, x) == 0) { return p; }
        
      }
    
    }  
    
  }
  
  static mpc_val_t *mpcaf_grammar_id(mpc_val_t *x, void *s) {
    
    mpca_grammar_st_t *st = s;
    mpc_parser_t *p = mpca_grammar_find_parser(x, st);
    free(x);
  
    if (p->name) {
      return mpca_state(mpca_root(mpca_add_tag(p, p->name)));
    } else {
      return mpca_state(mpca_root(p));
    }
  }
  
  mpc_parser_t *mpca_grammar_st(const char *grammar, mpca_grammar_st_t *st) {
    
    char *err_msg;
    mpc_parser_t *err_out;
    mpc_result_t r;
    mpc_parser_t *GrammarTotal, *Grammar, *Term, *Factor, *Base;
    
    GrammarTotal = mpc_new("grammar_total");
    Grammar = mpc_new("grammar");
    Term = mpc_new("term");
    Factor = mpc_new("factor");
    Base = mpc_new("base");
    
    mpc_define(GrammarTotal,
      mpc_predictive(mpc_total(Grammar, mpc_soft_delete))
    );
    
    mpc_define(Grammar, mpc_and(2, mpcaf_grammar_or,
      Term,
      mpc_maybe(mpc_and(2, mpcf_snd_free, mpc_sym("|"), Grammar, free)),
      mpc_soft_delete
    ));
    
    mpc_define(Term, mpc_many1(mpcaf_grammar_and, Factor));
    
    mpc_define(Factor, mpc_and(2, mpcaf_grammar_repeat,
      Base,
        mpc_or(6,
          mpc_sym("*"),
          mpc_sym("+"),
          mpc_sym("?"),
          mpc_sym("!"),
          mpc_tok_brackets(mpc_int(), free),
          mpc_pass()),
      mpc_soft_delete
    ));
    
    mpc_define(Base, mpc_or(5,
      mpc_apply_to(mpc_tok(mpc_string_lit()), mpcaf_grammar_string, st),
      mpc_apply_to(mpc_tok(mpc_char_lit()),   mpcaf_grammar_char, st),
      mpc_apply_to(mpc_tok(mpc_regex_lit()),  mpcaf_grammar_regex, st),
      mpc_apply_to(mpc_tok_braces(mpc_or(2, mpc_digits(), mpc_ident()), free), mpcaf_grammar_id, st),
      mpc_tok_parens(Grammar, mpc_soft_delete)
    ));
    
    mpc_optimise(GrammarTotal);
    mpc_optimise(Grammar);
    mpc_optimise(Factor);
    mpc_optimise(Term);
    mpc_optimise(Base);
    
    if(!mpc_parse("<mpc_grammar_compiler>", grammar, GrammarTotal, &r)) {
      err_msg = mpc_err_string(r.error);
      err_out = mpc_failf("Invalid Grammar: %s", err_msg);
      mpc_err_delete(r.error);
      free(err_msg);
      r.output = err_out;
    }
    
    mpc_cleanup(5, GrammarTotal, Grammar, Term, Factor, Base);
    
    mpc_optimise(r.output);
    
    return (st->flags & MPCA_LANG_PREDICTIVE) ? mpc_predictive(r.output) : r.output;
    
  }
  
  mpc_parser_t *mpca_grammar(int flags, const char *grammar, ...) {
    mpca_grammar_st_t st;
    mpc_parser_t *res;
    va_list va;
    va_start(va, grammar);
    
    st.va = &va;
    st.parsers_num = 0;
    st.parsers = NULL;
    st.flags = flags;
    
    res = mpca_grammar_st(grammar, &st);  
    free(st.parsers);
    va_end(va);
    return res;
  }
  
  typedef struct {
    char *ident;
    char *name;
    mpc_parser_t *grammar;
  } mpca_stmt_t;
  
  static mpc_val_t *mpca_stmt_afold(int n, mpc_val_t **xs) {
    mpca_stmt_t *stmt = allocate(sizeof(mpca_stmt_t));
    stmt->ident = ((char**)xs)[0];
    stmt->name = ((char**)xs)[1];
    stmt->grammar = ((mpc_parser_t**)xs)[3];
    (void) n;
    free(((char**)xs)[2]);
    free(((char**)xs)[4]);
    
    return stmt;
  }
  
  static mpc_val_t *mpca_stmt_fold(int n, mpc_val_t **xs) {
    
    int i;
    mpca_stmt_t **stmts = allocate(sizeof(mpca_stmt_t*) * (n+1));
    
    for (i = 0; i < n; i++) {
      stmts[i] = xs[i];
    }
    stmts[n] = NULL;  
    
    return stmts;
  }
  
  static void mpca_stmt_list_delete(mpc_val_t *x) {
  
    mpca_stmt_t **stmts = x;
  
    while(*stmts) {
      mpca_stmt_t *stmt = *stmts; 
      free(stmt->ident);
      free(stmt->name);
      mpc_soft_delete(stmt->grammar);
      free(stmt);  
      stmts++;
    }
    free(x);
  
  }
  
  static mpc_val_t *mpca_stmt_list_apply_to(mpc_val_t *x, void *s) {
  
    mpca_grammar_st_t *st = s;
    mpca_stmt_t *stmt;
    mpca_stmt_t **stmts = x;
    mpc_parser_t *left;
  
    while(*stmts) {
      stmt = *stmts;
      left = mpca_grammar_find_parser(stmt->ident, st);
      if (st->flags & MPCA_LANG_PREDICTIVE) { stmt->grammar = mpc_predictive(stmt->grammar); }
      if (stmt->name) { stmt->grammar = mpc_expect(stmt->grammar, stmt->name); }
      mpc_optimise(stmt->grammar);
      mpc_define(left, stmt->grammar);
      free(stmt->ident);
      free(stmt->name);
      free(stmt);
      stmts++;
    }
    
    free(x);
    
    return NULL;
  }
  
  static mpc_err_t *mpca_lang_st(mpc_input_t *i, mpca_grammar_st_t *st) {
    
    mpc_result_t r;
    mpc_err_t *e;
    mpc_parser_t *Lang, *Stmt, *Grammar, *Term, *Factor, *Base; 
    
    Lang    = mpc_new("lang");
    Stmt    = mpc_new("stmt");
    Grammar = mpc_new("grammar");
    Term    = mpc_new("term");
    Factor  = mpc_new("factor");
    Base    = mpc_new("base");
    
    mpc_define(Lang, mpc_apply_to(
      mpc_total(mpc_predictive(mpc_many(mpca_stmt_fold, Stmt)), mpca_stmt_list_delete),
      mpca_stmt_list_apply_to, st
    ));
    
    mpc_define(Stmt, mpc_and(5, mpca_stmt_afold,
      mpc_tok(mpc_ident()), mpc_maybe(mpc_tok(mpc_string_lit())), mpc_sym(":"), Grammar, mpc_sym(";"),
      free, free, free, mpc_soft_delete
    ));
    
    mpc_define(Grammar, mpc_and(2, mpcaf_grammar_or,
        Term,
        mpc_maybe(mpc_and(2, mpcf_snd_free, mpc_sym("|"), Grammar, free)),
        mpc_soft_delete
    ));
    
    mpc_define(Term, mpc_many1(mpcaf_grammar_and, Factor));
    
    mpc_define(Factor, mpc_and(2, mpcaf_grammar_repeat,
      Base,
        mpc_or(6,
          mpc_sym("*"),
          mpc_sym("+"),
          mpc_sym("?"),
          mpc_sym("!"),
          mpc_tok_brackets(mpc_int(), free),
          mpc_pass()),
      mpc_soft_delete
    ));
    
    mpc_define(Base, mpc_or(5,
      mpc_apply_to(mpc_tok(mpc_string_lit()), mpcaf_grammar_string, st),
      mpc_apply_to(mpc_tok(mpc_char_lit()),   mpcaf_grammar_char, st),
      mpc_apply_to(mpc_tok(mpc_regex_lit()),  mpcaf_grammar_regex, st),
      mpc_apply_to(mpc_tok_braces(mpc_or(2, mpc_digits(), mpc_ident()), free), mpcaf_grammar_id, st),
      mpc_tok_parens(Grammar, mpc_soft_delete)
    ));
    
    mpc_optimise(Lang);
    mpc_optimise(Stmt);
    mpc_optimise(Grammar);
    mpc_optimise(Term);
    mpc_optimise(Factor);
    mpc_optimise(Base);
    
    if (!mpc_parse_input(i, Lang, &r)) {
      e = r.error;
    } else {
      e = NULL;
    }
    
    mpc_cleanup(6, Lang, Stmt, Grammar, Term, Factor, Base);
    
    return e;
  }
  
  mpc_err_t *mpca_lang_file(int flags, FILE *f, ...) {
    mpca_grammar_st_t st;
    mpc_input_t *i;
    mpc_err_t *err;
  
    va_list va;  
    va_start(va, f);
    
    st.va = &va;
    st.parsers_num = 0;
    st.parsers = NULL;
    st.flags = flags;
    
    i = mpc_input_new_file("<mpca_lang_file>", f);
    err = mpca_lang_st(i, &st);
    mpc_input_delete(i);
    
    free(st.parsers);
    va_end(va);
    return err;
  }
  
  mpc_err_t *mpca_lang_pipe(int flags, FILE *p, ...) {
    mpca_grammar_st_t st;
    mpc_input_t *i;
    mpc_err_t *err;
  
    va_list va;  
    va_start(va, p);
    
    st.va = &va;
    st.parsers_num = 0;
    st.parsers = NULL;
    st.flags = flags;
    
    i = mpc_input_new_pipe("<mpca_lang_pipe>", p);
    err = mpca_lang_st(i, &st);
    mpc_input_delete(i);
    
    free(st.parsers);
    va_end(va);
    return err;
  }
  
  mpc_err_t *mpca_lang(int flags, const char *language, ...) {
    
    mpca_grammar_st_t st;
    mpc_input_t *i;
    mpc_err_t *err;
    
    va_list va;  
    va_start(va, language);
    
    st.va = &va;
    st.parsers_num = 0;
    st.parsers = NULL;
    st.flags = flags;
    
    i = mpc_input_new_string("<mpca_lang>", language);
    err = mpca_lang_st(i, &st);
    mpc_input_delete(i);
    
    free(st.parsers);
    va_end(va);
    return err;
  }
  
  mpc_err_t *mpca_lang_contents(int flags, const char *filename, ...) {
    
    mpca_grammar_st_t st;
    mpc_input_t *i;
    mpc_err_t *err;
    
    va_list va;
  
    FILE *f = fopen(filename, "rb");
    
    if (f == NULL) {
      err = mpc_err_file(filename, "Unable to open file!");
      return err;
    }
    
    va_start(va, filename);
    
    st.va = &va;
    st.parsers_num = 0;
    st.parsers = NULL;
    st.flags = flags;
    
    i = mpc_input_new_file(filename, f);
    err = mpca_lang_st(i, &st);
    mpc_input_delete(i);
    
    free(st.parsers);
    va_end(va);  
    
    fclose(f);
    
    return err;
  }
  
  static int mpc_nodecount_unretained(mpc_parser_t* p, int force) {
  
    int i, total;
  
    if (p->retained && !force) { return 0; }
  
    if (p->type == MPC_TYPE_EXPECT) { return 1 + mpc_nodecount_unretained(p->data.expect.x, 0); }
  
    if (p->type == MPC_TYPE_APPLY)    { return 1 + mpc_nodecount_unretained(p->data.apply.x, 0); }
    if (p->type == MPC_TYPE_APPLY_TO) { return 1 + mpc_nodecount_unretained(p->data.apply_to.x, 0); }
    if (p->type == MPC_TYPE_PREDICT)  { return 1 + mpc_nodecount_unretained(p->data.predict.x, 0); }
  
    if (p->type == MPC_TYPE_NOT)   { return 1 + mpc_nodecount_unretained(p->data.not.x, 0); }
    if (p->type == MPC_TYPE_MAYBE) { return 1 + mpc_nodecount_unretained(p->data.not.x, 0); }
  
    if (p->type == MPC_TYPE_MANY)  { return 1 + mpc_nodecount_unretained(p->data.repeat.x, 0); }
    if (p->type == MPC_TYPE_MANY1) { return 1 + mpc_nodecount_unretained(p->data.repeat.x, 0); }
    if (p->type == MPC_TYPE_COUNT) { return 1 + mpc_nodecount_unretained(p->data.repeat.x, 0); }
  
    if (p->type == MPC_TYPE_OR) { 
      total = 0;
      for(i = 0; i < p->data.or.n; i++) {
        total += mpc_nodecount_unretained(p->data.or.xs[i], 0);
      }
      return total;
    }
    
    if (p->type == MPC_TYPE_AND) {
      total = 0;
      for(i = 0; i < p->data.and.n; i++) {
        total += mpc_nodecount_unretained(p->data.and.xs[i], 0);
      }
      return total;
    }
  
    return 1;
    
  }
  
  void mpc_stats(mpc_parser_t* p) {
    printf("Stats\n");
    printf("=====\n");
    printf("Node Count: %i\n", mpc_nodecount_unretained(p, 1));
  }
  
  static void mpc_optimise_unretained(mpc_parser_t *p, int force) {
    
    int i, n, m;
    mpc_parser_t *t;
    
    if (p->retained && !force) { return; }
    
    /* Optimise Subexpressions */
    
    if (p->type == MPC_TYPE_EXPECT)   { mpc_optimise_unretained(p->data.expect.x, 0); }
    if (p->type == MPC_TYPE_APPLY)    { mpc_optimise_unretained(p->data.apply.x, 0); }
    if (p->type == MPC_TYPE_APPLY_TO) { mpc_optimise_unretained(p->data.apply_to.x, 0); }
    if (p->type == MPC_TYPE_PREDICT)  { mpc_optimise_unretained(p->data.predict.x, 0); }
    if (p->type == MPC_TYPE_NOT)      { mpc_optimise_unretained(p->data.not.x, 0); }
    if (p->type == MPC_TYPE_MAYBE)    { mpc_optimise_unretained(p->data.not.x, 0); }
    if (p->type == MPC_TYPE_MANY)     { mpc_optimise_unretained(p->data.repeat.x, 0); }
    if (p->type == MPC_TYPE_MANY1)    { mpc_optimise_unretained(p->data.repeat.x, 0); }
    if (p->type == MPC_TYPE_COUNT)    { mpc_optimise_unretained(p->data.repeat.x, 0); }
    
    if (p->type == MPC_TYPE_OR) { 
      for(i = 0; i < p->data.or.n; i++) {
        mpc_optimise_unretained(p->data.or.xs[i], 0);
      }
    }
    
    if (p->type == MPC_TYPE_AND) {
      for(i = 0; i < p->data.and.n; i++) {
        mpc_optimise_unretained(p->data.and.xs[i], 0);
      }
    }  
    
    /* Perform optimisations */
    
    while (1) {
      
      /* Merge rhs `or` */
      if (p->type == MPC_TYPE_OR
      &&  p->data.or.xs[p->data.or.n-1]->type == MPC_TYPE_OR
      && !p->data.or.xs[p->data.or.n-1]->retained) {
        t = p->data.or.xs[p->data.or.n-1];
        n = p->data.or.n; m = t->data.or.n;
        p->data.or.n = n + m - 1;
        p->data.or.xs = reallocate(p->data.or.xs, sizeof(mpc_parser_t*) * (n + m -1));
        memmove(p->data.or.xs + n - 1, t->data.or.xs, m * sizeof(mpc_parser_t*));
        free(t->data.or.xs); free(t->name); free(t);
        continue;
      }
  
      /* Merge lhs `or` */
      if (p->type == MPC_TYPE_OR
      &&  p->data.or.xs[0]->type == MPC_TYPE_OR
      && !p->data.or.xs[0]->retained) {
        t = p->data.or.xs[0];
        n = p->data.or.n; m = t->data.or.n;
        p->data.or.n = n + m - 1;
        p->data.or.xs = reallocate(p->data.or.xs, sizeof(mpc_parser_t*) * (n + m -1));
        memmove(p->data.or.xs + m, t->data.or.xs + 1, n * sizeof(mpc_parser_t*));
        memmove(p->data.or.xs, t->data.or.xs, m * sizeof(mpc_parser_t*));
        free(t->data.or.xs); free(t->name); free(t);
        continue;
      }
      
      /* Remove ast `pass` */
      if (p->type == MPC_TYPE_AND
      &&  p->data.and.n == 2
      &&  p->data.and.xs[0]->type == MPC_TYPE_PASS
      && !p->data.and.xs[0]->retained
      &&  p->data.and.f == mpcf_fold_ast) {
        t = p->data.and.xs[1];
        mpc_delete(p->data.and.xs[0]);
        free(p->data.and.xs); free(p->data.and.dxs); free(p->name);
        memcpy(p, t, sizeof(mpc_parser_t));
        free(t);
        continue;
      }
      
      /* Merge ast lhs `and` */
      if (p->type == MPC_TYPE_AND
      &&  p->data.and.f == mpcf_fold_ast
      &&  p->data.and.xs[0]->type == MPC_TYPE_AND
      && !p->data.and.xs[0]->retained
      &&  p->data.and.xs[0]->data.and.f == mpcf_fold_ast) {
        t = p->data.and.xs[0];
        n = p->data.and.n; m = t->data.and.n;
        p->data.and.n = n + m - 1;
        p->data.and.xs = reallocate(p->data.and.xs, sizeof(mpc_parser_t*) * (n + m - 1));
        p->data.and.dxs = reallocate(p->data.and.dxs, sizeof(mpc_dtor_t) * (n + m - 1 - 1));
        memmove(p->data.and.xs + m, p->data.and.xs + 1, (n - 1) * sizeof(mpc_parser_t*));
        memmove(p->data.and.xs, t->data.and.xs, m * sizeof(mpc_parser_t*));
        for (i = 0; i < p->data.and.n-1; i++) { p->data.and.dxs[i] = (mpc_dtor_t)mpc_ast_delete; }
        free(t->data.and.xs); free(t->data.and.dxs); free(t->name); free(t); 
        continue;
      }
      
      /* Merge ast rhs `and` */
      if (p->type == MPC_TYPE_AND
      &&  p->data.and.f == mpcf_fold_ast
      &&  p->data.and.xs[p->data.and.n-1]->type == MPC_TYPE_AND
      && !p->data.and.xs[p->data.and.n-1]->retained
      &&  p->data.and.xs[p->data.and.n-1]->data.and.f == mpcf_fold_ast) {
        t = p->data.and.xs[p->data.and.n-1];
        n = p->data.and.n; m = t->data.and.n;
        p->data.and.n = n + m - 1;
        p->data.and.xs = reallocate(p->data.and.xs, sizeof(mpc_parser_t*) * (n + m -1));
        p->data.and.dxs = reallocate(p->data.and.dxs, sizeof(mpc_dtor_t) * (n + m - 1 - 1));
        memmove(p->data.and.xs + n - 1, t->data.and.xs, m * sizeof(mpc_parser_t*));
        for (i = 0; i < p->data.and.n-1; i++) { p->data.and.dxs[i] = (mpc_dtor_t)mpc_ast_delete; }
        free(t->data.and.xs); free(t->data.and.dxs); free(t->name); free(t); 
        continue;
      }
  
      /* Remove re `lift` */
      if (p->type == MPC_TYPE_AND
      &&  p->data.and.n == 2
      &&  p->data.and.xs[0]->type == MPC_TYPE_LIFT
      &&  p->data.and.xs[0]->data.lift.lf == mpcf_ctor_str
      && !p->data.and.xs[0]->retained
      &&  p->data.and.f == mpcf_strfold) {
        t = p->data.and.xs[1];
        mpc_delete(p->data.and.xs[0]);
        free(p->data.and.xs); free(p->data.and.dxs); free(p->name);
        memcpy(p, t, sizeof(mpc_parser_t));
        free(t);
        continue;
      }
  
      /* Merge re lhs `and` */
      if (p->type == MPC_TYPE_AND
      &&  p->data.and.f == mpcf_strfold
      &&  p->data.and.xs[0]->type == MPC_TYPE_AND
      && !p->data.and.xs[0]->retained
      &&  p->data.and.xs[0]->data.and.f == mpcf_strfold) {
        t = p->data.and.xs[0];
        n = p->data.and.n; m = t->data.and.n;
        p->data.and.n = n + m - 1;
        p->data.and.xs = reallocate(p->data.and.xs, sizeof(mpc_parser_t*) * (n + m - 1));
        p->data.and.dxs = reallocate(p->data.and.dxs, sizeof(mpc_dtor_t) * (n + m - 1 - 1));
        memmove(p->data.and.xs + m, p->data.and.xs + 1, (n - 1) * sizeof(mpc_parser_t*));
        memmove(p->data.and.xs, t->data.and.xs, m * sizeof(mpc_parser_t*));
        for (i = 0; i < p->data.and.n-1; i++) { p->data.and.dxs[i] = free; }
        free(t->data.and.xs); free(t->data.and.dxs); free(t->name); free(t); 
        continue;
      }
      
      /* Merge re rhs `and` */
      if (p->type == MPC_TYPE_AND
      &&  p->data.and.f == mpcf_strfold
      &&  p->data.and.xs[p->data.and.n-1]->type == MPC_TYPE_AND
      && !p->data.and.xs[p->data.and.n-1]->retained
      &&  p->data.and.xs[p->data.and.n-1]->data.and.f == mpcf_strfold) {
        t = p->data.and.xs[p->data.and.n-1];
        n = p->data.and.n; m = t->data.and.n;
        p->data.and.n = n + m - 1;
        p->data.and.xs = reallocate(p->data.and.xs, sizeof(mpc_parser_t*) * (n + m -1));
        p->data.and.dxs = reallocate(p->data.and.dxs, sizeof(mpc_dtor_t) * (n + m - 1 - 1));
        memmove(p->data.and.xs + n - 1, t->data.and.xs, m * sizeof(mpc_parser_t*));
        for (i = 0; i < p->data.and.n-1; i++) { p->data.and.dxs[i] = free; }
        free(t->data.and.xs); free(t->data.and.dxs); free(t->name); free(t); 
        continue;
      }
      
      return;
      
    }
    
  }
  
  void mpc_optimise(mpc_parser_t *p) {
    mpc_optimise_unretained(p, 1);
  }
  
  