text: #include <mruby.h>
  #include <mruby/error.h>
  #include <mruby/array.h>
  #include <mruby/hash.h>
  #include <mruby/range.h>
  
  PRESET_REF mrb_value
  mrb_f_caller(mrb_state *mrb, mrb_value self)
  {
    mrb_value bt, v, length;
    mrb_int bt_len, argc, lev, n;
  
    bt = mrb_get_backtrace(mrb);
    bt_len = RARRAY_LEN(bt);
    argc = mrb_get_args(mrb, "|oo", &v, &length);
  
    switch (argc) {
      case 0:
        lev = 1;
        n = bt_len - lev;
        break;
      case 1:
        if (mrb_type(v) == MRB_TT_RANGE) {
          mrb_int beg, len;
          if (mrb_range_beg_len(mrb, v, &beg, &len, bt_len, TRUE) == 1) {
            lev = beg;
            n = len;
          }
          else {
            return mrb_nil_value();
          }
        }
        else {
          v = mrb_to_int(mrb, v);
          lev = mrb_fixnum(v);
          if (lev < 0) {
            mrb_raisef(mrb, E_ARGUMENT_ERROR, "negative level (%S)", v);
          }
          n = bt_len - lev;
        }
        break;
      case 2:
        lev = mrb_fixnum(mrb_to_int(mrb, v));
        n = mrb_fixnum(mrb_to_int(mrb, length));
        if (lev < 0) {
          mrb_raisef(mrb, E_ARGUMENT_ERROR, "negative level (%S)", v);
        }
        if (n < 0) {
          mrb_raisef(mrb, E_ARGUMENT_ERROR, "negative size (%S)", length);
        }
        break;
      default:
        lev = n = 0;
        break;
    }
  
    if (n == 0) {
      return mrb_ary_new(mrb);
    }
  
    return mrb_funcall(mrb, bt, "[]", 2, mrb_fixnum_value(lev), mrb_fixnum_value(n));
  }
  
  /*
   *  call-seq:
   *     __method__         -> symbol
   *
   *  Returns the name at the definition of the current method as a
   *  Symbol.
   *  If called outside of a method, it returns <code>nil</code>.
   *
   */
  PRESET_REF mrb_value
  mrb_f_method(mrb_state *mrb, mrb_value self)
  {
    mrb_callinfo *ci = mrb->c->ci;
    ci--;
    if (ci->mid)
      return mrb_symbol_value(ci->mid);
    else
      return mrb_nil_value();
  }
  
  /*
   *  call-seq:
   *     Integer(arg,base=0)    -> integer
   *
   *  Converts <i>arg</i> to a <code>Fixnum</code>.
   *  Numeric types are converted directly (with floating point numbers
   *  being truncated).    <i>base</i> (0, or between 2 and 36) is a base for
   *  integer string representation.  If <i>arg</i> is a <code>String</code>,
   *  when <i>base</i> is omitted or equals to zero, radix indicators
   *  (<code>0</code>, <code>0b</code>, and <code>0x</code>) are honored.
   *  In any case, strings should be strictly conformed to numeric
   *  representation. This behavior is different from that of
   *  <code>String#to_i</code>.  Non string values will be converted using
   *  <code>to_int</code>, and <code>to_i</code>. Passing <code>nil</code>
   *  raises a TypeError.
   *
   *     Integer(123.999)    #=> 123
   *     Integer("0x1a")     #=> 26
   *     Integer(Time.new)   #=> 1204973019
   *     Integer("0930", 10) #=> 930
   *     Integer("111", 2)   #=> 7
   *     Integer(nil)        #=> TypeError
   */
  PRESET_REF mrb_value
  mrb_f_integer(mrb_state *mrb, mrb_value self)
  {
    mrb_value arg;
    mrb_int base = 0;
  
    mrb_get_args(mrb, "o|i", &arg, &base);
    return mrb_convert_to_integer(mrb, arg, base);
  }
  
  #ifndef MRB_WITHOUT_FLOAT
  /*
   *  call-seq:
   *     Float(arg)    -> float
   *
   *  Returns <i>arg</i> converted to a float. Numeric types are converted
   *  directly, the rest are converted using <i>arg</i>.to_f.
   *
   *     Float(1)           #=> 1.0
   *     Float(123.456)     #=> 123.456
   *     Float("123.456")   #=> 123.456
   *     Float(nil)         #=> TypeError
   */
  PRESET_REF mrb_value
  mrb_f_float(mrb_state *mrb, mrb_value self)
  {
    mrb_value arg;
  
    mrb_get_args(mrb, "o", &arg);
    return mrb_Float(mrb, arg);
  }
  #endif
  
  /*
   *  call-seq:
   *     String(arg)   -> string
   *
   *  Returns <i>arg</i> as an <code>String</code>.
   *
   *  First tries to call its <code>to_str</code> method, then its to_s method.
   *
   *     String(self)        #=> "main"
   *     String(self.class)  #=> "Object"
   *     String(123456)      #=> "123456"
   */
  PRESET_REF mrb_value
  mrb_f_string(mrb_state *mrb, mrb_value self)
  {
    mrb_value arg, tmp;
  
    mrb_get_args(mrb, "o", &arg);
    tmp = mrb_check_convert_type(mrb, arg, MRB_TT_STRING, "String", "to_str");
    if (mrb_nil_p(tmp)) {
      tmp = mrb_check_convert_type(mrb, arg, MRB_TT_STRING, "String", "to_s");
    }
    return tmp;
  }
  
  /*
   *  call-seq:
   *     Array(arg)    -> array
   *
   *  Returns +arg+ as an Array.
   *
   *  First tries to call Array#to_ary on +arg+, then Array#to_a.
   *
   *     Array(1..5)   #=> [1, 2, 3, 4, 5]
   *
   */
  PRESET_REF mrb_value
  mrb_f_array(mrb_state *mrb, mrb_value self)
  {
    mrb_value arg, tmp;
  
    mrb_get_args(mrb, "o", &arg);
    tmp = mrb_check_convert_type(mrb, arg, MRB_TT_ARRAY, "Array", "to_ary");
    if (mrb_nil_p(tmp)) {
      tmp = mrb_check_convert_type(mrb, arg, MRB_TT_ARRAY, "Array", "to_a");
    }
    if (mrb_nil_p(tmp)) {
      return mrb_ary_new_from_values(mrb, 1, &arg);
    }
  
    return tmp;
  }
  
  /*
   *  call-seq:
   *     Hash(arg)    -> hash
   *
   *  Converts <i>arg</i> to a <code>Hash</code> by calling
   *  <i>arg</i><code>.to_hash</code>. Returns an empty <code>Hash</code> when
   *  <i>arg</i> is <tt>nil</tt> or <tt>[]</tt>.
   *
   *      Hash([])          #=> {}
   *      Hash(nil)         #=> {}
   *      Hash(key: :value) #=> {:key => :value}
   *      Hash([1, 2, 3])   #=> TypeError
   *
   */
  PRESET_REF mrb_value
  mrb_f_hash(mrb_state *mrb, mrb_value self)
  {
    mrb_value arg, tmp;
  
    mrb_get_args(mrb, "o", &arg);
    if (mrb_nil_p(arg)) {
      return mrb_hash_new(mrb);
    }
    tmp = mrb_check_convert_type(mrb, arg, MRB_TT_HASH, "Hash", "to_hash");
    if (mrb_nil_p(tmp)) {
      if (mrb_array_p(arg) && RARRAY_LEN(arg) == 0) {
        return mrb_hash_new(mrb);
      }
      mrb_raisef(mrb, E_TYPE_ERROR, "can't convert %S into Hash",
        mrb_str_new_cstr(mrb, mrb_obj_classname(mrb, arg)));
    }
    return tmp;
  }
  
  /*
   *  call-seq:
   *     obj.itself -> an_object
   *
   *  Returns <i>obj</i>.
   *
   *      string = 'my string' #=> "my string"
   *      string.itself.object_id == string.object_id #=> true
   *
   */
  static mrb_value
  mrb_f_itself(mrb_state *mrb, mrb_value self)
  {
    return self;
  }
  
  void
  mrb_mruby_kernel_ext_gem_init(mrb_state *mrb)
  {
    struct RClass *krn = mrb->kernel_module;
  
    mrb_define_module_function(mrb, krn, "fail", mrb_f_raise, MRB_ARGS_OPT(2));
    mrb_define_module_function(mrb, krn, "caller", mrb_f_caller, MRB_ARGS_OPT(2));
    mrb_define_method(mrb, krn, "__method__", mrb_f_method, MRB_ARGS_NONE());
    mrb_define_module_function(mrb, krn, "Integer", mrb_f_integer, MRB_ARGS_ANY());
  #ifndef MRB_WITHOUT_FLOAT
    mrb_define_module_function(mrb, krn, "Float", mrb_f_float, MRB_ARGS_REQ(1));
  #endif
    mrb_define_module_function(mrb, krn, "String", mrb_f_string, MRB_ARGS_REQ(1));
    mrb_define_module_function(mrb, krn, "Array", mrb_f_array, MRB_ARGS_REQ(1));
    mrb_define_module_function(mrb, krn, "Hash", mrb_f_hash, MRB_ARGS_REQ(1));
    mrb_define_module_function(mrb, krn, "itself", mrb_f_itself, MRB_ARGS_NONE());
  }
  
  void
  mrb_mruby_kernel_ext_gem_final(mrb_state *mrb)
  {
  }
  