text: #include <math.h>
  
  // TODO(bill): Big numbers
  // IMPORTANT TODO(bill): This needs to be completely fixed!!!!!!!!
  
  gb_global BlockingMutex hash_exact_value_mutex;
  
  struct Ast;
  struct HashKey;
  struct Type;
  struct Entity;
  bool are_types_identical(Type *x, Type *y);
  
  struct Complex128 {
  	f64 real, imag;
  };
  struct Quaternion256 {
  	f64 imag, jmag, kmag, real;
  };
  
  Quaternion256 quaternion256_inverse(Quaternion256 x) {
  	f64 invmag2 = 1.0 / (x.real*x.real + x.imag*x.imag + x.jmag*x.jmag + x.kmag*x.kmag);
  	x.real = +x.real * invmag2;
  	x.imag = -x.imag * invmag2;
  	x.jmag = -x.jmag * invmag2;
  	x.kmag = -x.kmag * invmag2;
  	return x;
  }
  
  
  enum ExactValueKind {
  	ExactValue_Invalid    = 0,
  
  	ExactValue_Bool       = 1,
  	ExactValue_String     = 2,
  	ExactValue_Integer    = 3,
  	ExactValue_Float      = 4,
  	ExactValue_Complex    = 5,
  	ExactValue_Quaternion = 6,
  	ExactValue_Pointer    = 7,
  	ExactValue_Compound   = 8,  // TODO(bill): Is this good enough?
  	ExactValue_Procedure  = 9, // TODO(bill): Is this good enough?
  	ExactValue_Typeid     = 10,
  
  	ExactValue_Count,
  };
  
  struct ExactValue {
  	ExactValueKind kind;
  	union {
  		bool           value_bool;
  		String         value_string;
  		BigInt         value_integer; // NOTE(bill): This must be an integer and not a pointer
  		f64            value_float;
  		i64            value_pointer;
  		Complex128    *value_complex;
  		Quaternion256 *value_quaternion;
  		Ast *          value_compound;
  		Ast *          value_procedure;
  		Type *         value_typeid;
  	};
  };
  
  gb_global ExactValue const empty_exact_value = {};
  
  HashKey hash_exact_value(ExactValue v) {
  	mutex_lock(&hash_exact_value_mutex);
  	defer (mutex_unlock(&hash_exact_value_mutex));
  	
  	HashKey empty = {};
  	switch (v.kind) {
  	case ExactValue_Invalid:
  		return empty;
  	case ExactValue_Bool:
  		return hash_integer(u64(v.value_bool));
  	case ExactValue_String:
  		{
  			char const *str = string_intern(v.value_string);
  			return hash_pointer(str);
  		}
  	case ExactValue_Integer:
  		{
  			HashKey key = hashing_proc(v.value_integer.dp, gb_size_of(*v.value_integer.dp) * v.value_integer.used);
  			u8 last = (u8)v.value_integer.sign;
  			key.key = (key.key ^ last) * 0x100000001b3ll;
  			return key;
  		}
  	case ExactValue_Float:
  		return hash_f64(v.value_float);
  	case ExactValue_Pointer:
  		return hash_integer(v.value_pointer);
  	case ExactValue_Complex:
  		return hashing_proc(v.value_complex, gb_size_of(Complex128));
  	case ExactValue_Quaternion:
  		return hashing_proc(v.value_quaternion, gb_size_of(Quaternion256));
  	case ExactValue_Compound:
  		return hash_pointer(v.value_compound);
  	case ExactValue_Procedure:
  		return hash_pointer(v.value_procedure);
  	case ExactValue_Typeid:
  		return hash_pointer(v.value_typeid);
  	}
  	return hashing_proc(&v, gb_size_of(ExactValue));
  
  }
  
  
  ExactValue exact_value_compound(Ast *node) {
  	ExactValue result = {ExactValue_Compound};
  	result.value_compound = node;
  	return result;
  }
  
  ExactValue exact_value_bool(bool b) {
  	ExactValue result = {ExactValue_Bool};
  	result.value_bool = (b != 0);
  	return result;
  }
  
  ExactValue exact_value_string(String string) {
  	// TODO(bill): Allow for numbers with underscores in them
  	ExactValue result = {ExactValue_String};
  	result.value_string = string;
  	return result;
  }
  
  ExactValue exact_value_i64(i64 i) {
  	ExactValue result = {ExactValue_Integer};
  	big_int_from_i64(&result.value_integer, i);
  	return result;
  }
  
  ExactValue exact_value_u64(u64 i) {
  	ExactValue result = {ExactValue_Integer};
  	big_int_from_u64(&result.value_integer, i);
  	return result;
  }
  
  ExactValue exact_value_float(f64 f) {
  	ExactValue result = {ExactValue_Float};
  	result.value_float = f;
  	return result;
  }
  
  ExactValue exact_value_complex(f64 real, f64 imag) {
  	ExactValue result = {ExactValue_Complex};
  	result.value_complex = gb_alloc_item(permanent_allocator(), Complex128);
  	result.value_complex->real = real;
  	result.value_complex->imag = imag;
  	return result;
  }
  
  ExactValue exact_value_quaternion(f64 real, f64 imag, f64 jmag, f64 kmag) {
  	ExactValue result = {ExactValue_Quaternion};
  	result.value_quaternion = gb_alloc_item(permanent_allocator(), Quaternion256);
  	result.value_quaternion->real = real;
  	result.value_quaternion->imag = imag;
  	result.value_quaternion->jmag = jmag;
  	result.value_quaternion->kmag = kmag;
  	return result;
  }
  
  ExactValue exact_value_pointer(i64 ptr) {
  	ExactValue result = {ExactValue_Pointer};
  	result.value_pointer = ptr;
  	return result;
  }
  
  ExactValue exact_value_procedure(Ast *node) {
  	ExactValue result = {ExactValue_Procedure};
  	result.value_procedure = node;
  	return result;
  }
  
  
  ExactValue exact_value_typeid(Type *type) {
  	ExactValue result = {ExactValue_Typeid};
  	result.value_typeid = type;
  	return result;
  }
  
  
  ExactValue exact_value_integer_from_string(String const &string) {
  	ExactValue result = {ExactValue_Integer};
  	big_int_from_string(&result.value_integer, string);
  	return result;
  }
  
  
  
  f64 float_from_string(String string) {
  	isize i = 0;
  	u8 *str = string.text;
  	isize len = string.len;
  
  	f64 sign = 1.0;
  	if (str[i] == '-') {
  		sign = -1.0;
  		i++;
  	} else if (*str == '+') {
  		i++;
  	}
  
  	f64 value = 0.0;
  	for (; i < len; i++) {
  		Rune r = cast(Rune)str[i];
  		if (r == '_') {
  			continue;
  		}
  		i64 v = digit_value(r);
  		if (v >= 10) {
  			break;
  		}
  		value *= 10.0;
  		value += v;
  	}
  
  	if (str[i] == '.') {
  		f64 pow10 = 10.0;
  		i++;
  		for (; i < string.len; i++) {
  			Rune r = cast(Rune)str[i];
  			if (r == '_') {
  				continue;
  			}
  			i64 v = digit_value(r);
  			if (v >= 10) {
  				break;
  			}
  			value += v/pow10;
  			pow10 *= 10.0;
  		}
  	}
  
  	bool frac = false;
  	f64 scale = 1.0;
  	if ((str[i] == 'e') || (str[i] == 'E')) {
  		i++;
  
  		if (str[i] == '-') {
  			frac = true;
  			i++;
  		} else if (str[i] == '+') {
  			i++;
  		}
  
  		u32 exp = 0;
  		for (; i < len; i++) {
  			Rune r = cast(Rune)str[i];
  			if (r == '_') {
  				continue;
  			}
  			u32 d = cast(u32)digit_value(r);
  			if (d >= 10) {
  				break;
  			}
  			exp = exp * 10 + d;
  		}
  		if (exp > 308) exp = 308;
  
  		while (exp >= 50) { scale *= 1e50; exp -= 50; }
  		while (exp >=  8) { scale *= 1e8;  exp -=  8; }
  		while (exp >   0) { scale *= 10.0; exp -=  1; }
  	}
  
  	return sign * (frac ? (value / scale) : (value * scale));
  }
  
  ExactValue exact_value_float_from_string(String string) {
  	if (string.len > 2 && string[0] == '0' && string[1] == 'h') {
  
  		isize digit_count = 0;
  		for (isize i = 2; i < string.len; i++) {
  			if (string[i] != '_') {
  				digit_count += 1;
  			}
  		}
  		u64 u = u64_from_string(string);
  		if (digit_count == 4) {
  			u16 x = cast(u16)u;
  			f32 f = f16_to_f32(x);
  			return exact_value_float(cast(f64)f);
  		} else if (digit_count == 8) {
  			u32 x = cast(u32)u;
  			f32 f = bit_cast<f32>(x);
  			return exact_value_float(cast(f64)f);
  		} else if (digit_count == 16) {
  			f64 f = bit_cast<f64>(u);
  			return exact_value_float(f);
  		} else {
  			GB_PANIC("Invalid hexadecimal float, expected 8 or 16 digits, got %td", digit_count);
  		}
  	}
  
  	if (!string_contains_char(string, '.') && !string_contains_char(string, '-')) {
  		// NOTE(bill): treat as integer
  		return exact_value_integer_from_string(string);
  	}
  
  	f64 f = float_from_string(string);
  	return exact_value_float(f);
  }
  
  
  ExactValue exact_value_from_basic_literal(TokenKind kind, String const &string) {
  	switch (kind) {
  	case Token_String:  return exact_value_string(string);
  	case Token_Integer: return exact_value_integer_from_string(string);
  	case Token_Float:   return exact_value_float_from_string(string);
  	case Token_Imag: {
  		String str = string;
  		Rune last_rune = cast(Rune)str[str.len-1];
  		str.len--; // Ignore the 'i|j|k'
  		f64 imag = float_from_string(str);
  
  		switch (last_rune) {
  		case 'i': return exact_value_complex(0, imag);
  		case 'j': return exact_value_quaternion(0, 0, imag, 0);
  		case 'k': return exact_value_quaternion(0, 0, 0, imag);
  		default: GB_PANIC("Invalid imaginary basic literal");
  		}
  	}
  	case Token_Rune: {
  		Rune r = GB_RUNE_INVALID;
  		utf8_decode(string.text, string.len, &r);
  		return exact_value_i64(r);
  	}
  	default:
  		GB_PANIC("Invalid token for basic literal");
  		break;
  	}
  
  	ExactValue result = {ExactValue_Invalid};
  	return result;
  }
  
  ExactValue exact_value_to_integer(ExactValue v) {
  	switch (v.kind) {
  	case ExactValue_Bool: {
  		i64 i = 0;
  		if (v.value_bool) {
  			i = 1;
  		}
  		return exact_value_i64(i);
  	}
  	case ExactValue_Integer:
  		return v;
  	case ExactValue_Float: {
  		i64 i = cast(i64)v.value_float;
  		f64 f = cast(f64)i;
  		if (f == v.value_float) {
  			return exact_value_i64(i);
  		}
  		break;
  	}
  
  	case ExactValue_Pointer:
  		return exact_value_i64(cast(i64)cast(intptr)v.value_pointer);
  	}
  	ExactValue r = {ExactValue_Invalid};
  	return r;
  }
  
  ExactValue exact_value_to_float(ExactValue v) {
  	switch (v.kind) {
  	case ExactValue_Integer:
  		return exact_value_float(big_int_to_f64(&v.value_integer));
  	case ExactValue_Float:
  		return v;
  	}
  	ExactValue r = {ExactValue_Invalid};
  	return r;
  }
  
  ExactValue exact_value_to_complex(ExactValue v) {
  	switch (v.kind) {
  	case ExactValue_Integer:
  		return exact_value_complex(big_int_to_f64(&v.value_integer), 0);
  	case ExactValue_Float:
  		return exact_value_complex(v.value_float, 0);
  	case ExactValue_Complex:
  		return v;
  	// case ExactValue_Quaternion:
  		// return exact_value_complex(v.value_quaternion.real, v.value_quaternion.imag);
  	}
  	ExactValue r = {ExactValue_Invalid};
  	v.value_complex = gb_alloc_item(permanent_allocator(), Complex128);
  	return r;
  }
  ExactValue exact_value_to_quaternion(ExactValue v) {
  	switch (v.kind) {
  	case ExactValue_Integer:
  		return exact_value_quaternion(big_int_to_f64(&v.value_integer), 0, 0, 0);
  	case ExactValue_Float:
  		return exact_value_quaternion(v.value_float, 0, 0, 0);
  	case ExactValue_Complex:
  		return exact_value_quaternion(v.value_complex->real, v.value_complex->imag, 0, 0);
  	case ExactValue_Quaternion:
  		return v;
  	}
  	ExactValue r = {ExactValue_Invalid};
  	v.value_quaternion = gb_alloc_item(permanent_allocator(), Quaternion256);
  	return r;
  }
  
  ExactValue exact_value_real(ExactValue v) {
  	switch (v.kind) {
  	case ExactValue_Integer:
  	case ExactValue_Float:
  		return v;
  	case ExactValue_Complex:
  		return exact_value_float(v.value_complex->real);
  	case ExactValue_Quaternion:
  		return exact_value_float(v.value_quaternion->real);
  	}
  	ExactValue r = {ExactValue_Invalid};
  	return r;
  }
  
  ExactValue exact_value_imag(ExactValue v) {
  	switch (v.kind) {
  	case ExactValue_Integer:
  	case ExactValue_Float:
  		return exact_value_i64(0);
  	case ExactValue_Complex:
  		return exact_value_float(v.value_complex->imag);
  	case ExactValue_Quaternion:
  		return exact_value_float(v.value_quaternion->imag);
  	}
  	ExactValue r = {ExactValue_Invalid};
  	return r;
  }
  
  ExactValue exact_value_jmag(ExactValue v) {
  	switch (v.kind) {
  	case ExactValue_Integer:
  	case ExactValue_Float:
  	case ExactValue_Complex:
  		return exact_value_i64(0);
  	case ExactValue_Quaternion:
  		return exact_value_float(v.value_quaternion->jmag);
  	}
  	ExactValue r = {ExactValue_Invalid};
  	return r;
  }
  
  ExactValue exact_value_kmag(ExactValue v) {
  	switch (v.kind) {
  	case ExactValue_Integer:
  	case ExactValue_Float:
  	case ExactValue_Complex:
  		return exact_value_i64(0);
  	case ExactValue_Quaternion:
  		return exact_value_float(v.value_quaternion->kmag);
  	}
  	ExactValue r = {ExactValue_Invalid};
  	return r;
  }
  
  ExactValue exact_value_make_imag(ExactValue v) {
  	switch (v.kind) {
  	case ExactValue_Integer:
  		return exact_value_complex(0, exact_value_to_float(v).value_float);
  	case ExactValue_Float:
  		return exact_value_complex(0, v.value_float);
  	default:
  		GB_PANIC("Expected an integer or float type for 'exact_value_make_imag'");
  	}
  	ExactValue r = {ExactValue_Invalid};
  	return r;
  }
  
  ExactValue exact_value_make_jmag(ExactValue v) {
  	switch (v.kind) {
  	case ExactValue_Integer:
  		return exact_value_quaternion(0, 0, exact_value_to_float(v).value_float, 0);
  	case ExactValue_Float:
  		return exact_value_quaternion(0, 0, v.value_float, 0);
  	default:
  		GB_PANIC("Expected an integer or float type for 'exact_value_make_imag'");
  	}
  	ExactValue r = {ExactValue_Invalid};
  	return r;
  }
  
  ExactValue exact_value_make_kmag(ExactValue v) {
  	switch (v.kind) {
  	case ExactValue_Integer:
  		return exact_value_quaternion(0, 0, 0, exact_value_to_float(v).value_float);
  	case ExactValue_Float:
  		return exact_value_quaternion(0, 0, 0, v.value_float);
  	default:
  		GB_PANIC("Expected an integer or float type for 'exact_value_make_imag'");
  	}
  	ExactValue r = {ExactValue_Invalid};
  	return r;
  }
  
  i64 exact_value_to_i64(ExactValue v) {
  	v = exact_value_to_integer(v);
  	if (v.kind == ExactValue_Integer) {
  		return big_int_to_i64(&v.value_integer);
  	}
  	return 0;
  }
  f64 exact_value_to_f64(ExactValue v) {
  	v = exact_value_to_float(v);
  	if (v.kind == ExactValue_Float) {
  		return v.value_float;
  	}
  	return 0.0;
  }
  
  
  
  
  
  
  ExactValue exact_unary_operator_value(TokenKind op, ExactValue v, i32 precision, bool is_unsigned) {
  	switch (op) {
  	case Token_Add:	{
  		switch (v.kind) {
  		case ExactValue_Invalid:
  		case ExactValue_Integer:
  		case ExactValue_Float:
  		case ExactValue_Complex:
  		case ExactValue_Quaternion:
  			return v;
  		}
  		break;
  	}
  
  	case Token_Sub:	{
  		switch (v.kind) {
  		case ExactValue_Invalid:
  			return v;
  		case ExactValue_Integer: {
  			ExactValue i = {ExactValue_Integer};
  			big_int_neg(&i.value_integer, &v.value_integer);
  			return i;
  		}
  		case ExactValue_Float: {
  			ExactValue i = v;
  			i.value_float = -i.value_float;
  			return i;
  		}
  		case ExactValue_Complex: {
  			f64 real = v.value_complex->real;
  			f64 imag = v.value_complex->imag;
  			return exact_value_complex(-real, -imag);
  		}
  		case ExactValue_Quaternion: {
  			f64 real = v.value_quaternion->real;
  			f64 imag = v.value_quaternion->imag;
  			f64 jmag = v.value_quaternion->jmag;
  			f64 kmag = v.value_quaternion->kmag;
  			return exact_value_quaternion(-real, -imag, -jmag, -kmag);
  		}
  		}
  		break;
  	}
  
  	case Token_Xor: {
  		switch (v.kind) {
  		case ExactValue_Invalid:
  			return v;
  		case ExactValue_Integer: {
  			GB_ASSERT(precision != 0);
  			ExactValue i = {ExactValue_Integer};
  			big_int_not(&i.value_integer, &v.value_integer, precision, !is_unsigned);
  			return i;
  		}
  		default:
  			goto failure;
  		}
  	}
  
  	case Token_Not: {
  		switch (v.kind) {
  		case ExactValue_Invalid: return v;
  		case ExactValue_Bool:
  			return exact_value_bool(!v.value_bool);
  		}
  		break;
  	}
  	}
  
  failure:
  	GB_PANIC("Invalid unary operation, %.*s", LIT(token_strings[op]));
  
  	ExactValue error_value = {};
  	return error_value;
  }
  
  // NOTE(bill): Make sure things are evaluated in correct order
  i32 exact_value_order(ExactValue const &v) {
  	switch (v.kind) {
  	case ExactValue_Invalid:
  		return 0;
  	case ExactValue_Bool:
  	case ExactValue_String:
  		return 1;
  	case ExactValue_Integer:
  		return 2;
  	case ExactValue_Float:
  		return 3;
  	case ExactValue_Complex:
  		return 4;
  	case ExactValue_Quaternion:
  		return 5;
  	case ExactValue_Pointer:
  		return 6;
  	case ExactValue_Procedure:
  		return 7;
  	// case ExactValue_Compound:
  		// return 8;
  
  	default:
  		GB_PANIC("How'd you get here? Invalid Value.kind %d", v.kind);
  		return -1;
  	}
  }
  
  void match_exact_values(ExactValue *x, ExactValue *y) {
  	if (exact_value_order(*y) < exact_value_order(*x)) {
  		match_exact_values(y, x);
  		return;
  	}
  
  	switch (x->kind) {
  	case ExactValue_Invalid:
  		*y = *x;
  		return;
  
  	case ExactValue_Bool:
  	case ExactValue_String:
  	case ExactValue_Quaternion:
  		return;
  
  	case ExactValue_Integer:
  		switch (y->kind) {
  		case ExactValue_Integer:
  			return;
  		case ExactValue_Float:
  			// TODO(bill): Is this good enough?
  			*x = exact_value_float(big_int_to_f64(&x->value_integer));
  			return;
  		case ExactValue_Complex:
  			*x = exact_value_complex(big_int_to_f64(&x->value_integer), 0);
  			return;
  		case ExactValue_Quaternion:
  			*x = exact_value_quaternion(big_int_to_f64(&x->value_integer), 0, 0, 0);
  			return;
  		}
  		break;
  
  	case ExactValue_Float:
  		switch (y->kind) {
  		case ExactValue_Float:
  			return;
  		case ExactValue_Complex:
  			*x = exact_value_to_complex(*x);
  			return;
  		case ExactValue_Quaternion:
  			*x = exact_value_to_quaternion(*x);
  			return;
  		}
  		break;
  
  	case ExactValue_Complex:
  		switch (y->kind) {
  		case ExactValue_Complex:
  			return;
  		case ExactValue_Quaternion:
  			*x = exact_value_to_quaternion(*x);
  			return;
  		}
  		break;
  
  	case ExactValue_Procedure:
  		return;
  	}
  
  	compiler_error("match_exact_values: How'd you get here? Invalid ExactValueKind %d", x->kind);
  }
  
  // TODO(bill): Allow for pointer arithmetic? Or are pointer slices good enough?
  ExactValue exact_binary_operator_value(TokenKind op, ExactValue x, ExactValue y) {
  	match_exact_values(&x, &y);
  
  	switch (x.kind) {
  	case ExactValue_Invalid:
  		return x;
  
  	case ExactValue_Bool:
  		switch (op) {
  		case Token_CmpAnd: return exact_value_bool(x.value_bool && y.value_bool);
  		case Token_CmpOr:  return exact_value_bool(x.value_bool || y.value_bool);
  		case Token_And:    return exact_value_bool(x.value_bool & y.value_bool);
  		case Token_Or:     return exact_value_bool(x.value_bool | y.value_bool);
  		case Token_AndNot: return exact_value_bool(x.value_bool & !y.value_bool);
  		case Token_Xor:    return exact_value_bool((x.value_bool && !y.value_bool) || (!x.value_bool && y.value_bool));
  		default: goto error;
  		}
  		break;
  
  	case ExactValue_Integer: {
  		BigInt const *a = &x.value_integer;
  		BigInt const *b = &y.value_integer;
  		BigInt c = {};
  		switch (op) {
  		case Token_Add:    big_int_add(&c, a, b); break;
  		case Token_Sub:    big_int_sub(&c, a, b); break;
  		case Token_Mul:    big_int_mul(&c, a, b); break;
  		case Token_Quo:    return exact_value_float(fmod(big_int_to_f64(a), big_int_to_f64(b)));
  		case Token_QuoEq:  big_int_quo(&c, a, b); break; // NOTE(bill): Integer division
  		case Token_Mod:    big_int_rem(&c, a, b); break;
  		case Token_ModMod: big_int_euclidean_mod(&c, a, b); break;
  		case Token_And:    big_int_and(&c, a, b);     break;
  		case Token_Or:     big_int_or(&c, a, b);      break;
  		case Token_Xor:    big_int_xor(&c, a, b);     break;
  		case Token_AndNot: big_int_and_not(&c, a, b); break;
  		case Token_Shl:    big_int_shl(&c, a, b);     break;
  		case Token_Shr:    big_int_shr(&c, a, b);     break;
  		default: goto error;
  		}
  		ExactValue res = {ExactValue_Integer};
  		res.value_integer = c;
  		return res;
  	}
  
  	case ExactValue_Float: {
  		f64 a = x.value_float;
  		f64 b = y.value_float;
  		switch (op) {
  		case Token_Add: return exact_value_float(a + b);
  		case Token_Sub: return exact_value_float(a - b);
  		case Token_Mul: return exact_value_float(a * b);
  		case Token_Quo: return exact_value_float(a / b);
  		default: goto error;
  		}
  		break;
  	}
  
  	case ExactValue_Complex: {
  		y = exact_value_to_complex(y);
  		f64 a = x.value_complex->real;
  		f64 b = x.value_complex->imag;
  		f64 c = y.value_complex->real;
  		f64 d = y.value_complex->imag;
  		f64 real = 0;
  		f64 imag = 0;
  		switch (op) {
  		case Token_Add:
  			real = a + c;
  			imag = b + d;
  			break;
  		case Token_Sub:
  			real = a - c;
  			imag = b - d;
  			break;
  		case Token_Mul:
  			real = (a*c - b*d);
  			imag = (b*c + a*d);
  			break;
  		case Token_Quo: {
  			f64 s = c*c + d*d;
  			real = (a*c + b*d)/s;
  			imag = (b*c - a*d)/s;
  			break;
  		}
  		default: goto error;
  		}
  		return exact_value_complex(real, imag);
  		break;
  	}
  
  	case ExactValue_Quaternion: {
  		y = exact_value_to_quaternion(y);
  		f64 xr = x.value_quaternion->real;
  		f64 xi = x.value_quaternion->imag;
  		f64 xj = x.value_quaternion->jmag;
  		f64 xk = x.value_quaternion->kmag;
  		f64 yr = y.value_quaternion->real;
  		f64 yi = y.value_quaternion->imag;
  		f64 yj = y.value_quaternion->jmag;
  		f64 yk = y.value_quaternion->kmag;
  
  
  		f64 real = 0;
  		f64 imag = 0;
  		f64 jmag = 0;
  		f64 kmag = 0;
  
  		switch (op) {
  		case Token_Add:
  			real = xr + yr;
  			imag = xi + yi;
  			jmag = xj + yj;
  			kmag = xk + yk;
  			break;
  		case Token_Sub:
  			real = xr - yr;
  			imag = xi - yi;
  			jmag = xj - yj;
  			kmag = xk - yk;
  			break;
  		case Token_Mul:
  			imag = xr * yi + xi * yr + xj * yk - xk * yj;
  			jmag = xr * yj - xi * yk + xj * yr + xk * yi;
  			kmag = xr * yk + xi * yj - xj * yi + xk * yr;
  			real = xr * yr - xi * yi - xj * yj - xk * yk;
  			break;
  		case Token_Quo: {
  			f64 invmag2 = 1.0 / (yr*yr + yi*yi + yj*yj + yk*yk);
  			imag = (xr * -yi + xi * +yr + xj * -yk - xk * -yj) * invmag2;
  			jmag = (xr * -yj - xi * -yk + xj * +yr + xk * -yi) * invmag2;
  			kmag = (xr * -yk + xi * -yj - xj * -yi + xk * +yr) * invmag2;
  			real = (xr * +yr - xi * -yi - xj * -yj - xk * -yk) * invmag2;
  			break;
  		}
  		default: goto error;
  		}
  		return exact_value_quaternion(real, imag, jmag, kmag);
  		break;
  	}
  
  	case ExactValue_String: {
  		if (op != Token_Add) goto error;
  
  		// NOTE(bill): How do you minimize this over allocation?
  		String sx = x.value_string;
  		String sy = y.value_string;
  		isize len = sx.len+sy.len;
  		u8 *data = gb_alloc_array(heap_allocator(), u8, len);
  		gb_memmove(data,        sx.text, sx.len);
  		gb_memmove(data+sx.len, sy.text, sy.len);
  		return exact_value_string(make_string(data, len));
  		break;
  	}
  	}
  
  error:; // NOTE(bill): MSVC accepts this??? apparently you cannot declare variables immediately after labels...
  	return empty_exact_value;
  }
  
  gb_inline ExactValue exact_value_add(ExactValue const &x, ExactValue const &y) {
  	return exact_binary_operator_value(Token_Add, x, y);
  }
  gb_inline ExactValue exact_value_sub(ExactValue const &x, ExactValue const &y) {
  	return exact_binary_operator_value(Token_Sub, x, y);
  }
  gb_inline ExactValue exact_value_mul(ExactValue const &x, ExactValue const &y) {
  	return exact_binary_operator_value(Token_Mul, x, y);
  }
  gb_inline ExactValue exact_value_quo(ExactValue const &x, ExactValue const &y) {
  	return exact_binary_operator_value(Token_Quo, x, y);
  }
  gb_inline ExactValue exact_value_shift(TokenKind op, ExactValue const &x, ExactValue const &y) {
  	return exact_binary_operator_value(op, x, y);
  }
  
  gb_inline ExactValue exact_value_increment_one(ExactValue const &x) {
  	return exact_binary_operator_value(Token_Add, x, exact_value_i64(1));
  }
  
  
  i32 cmp_f64(f64 a, f64 b) {
  	return (a > b) - (a < b);
  }
  
  bool compare_exact_values(TokenKind op, ExactValue x, ExactValue y) {
  	match_exact_values(&x, &y);
  
  	switch (x.kind) {
  	case ExactValue_Invalid:
  		return false;
  
  	case ExactValue_Bool:
  		switch (op) {
  		case Token_CmpEq: return x.value_bool == y.value_bool;
  		case Token_NotEq: return x.value_bool != y.value_bool;
  		}
  		break;
  
  	case ExactValue_Integer: {
  		i32 cmp = big_int_cmp(&x.value_integer, &y.value_integer);
  		switch (op) {
  		case Token_CmpEq: return cmp == 0;
  		case Token_NotEq: return cmp != 0;
  		case Token_Lt:    return cmp <  0;
  		case Token_LtEq:  return cmp <= 0;
  		case Token_Gt:    return cmp >  0;
  		case Token_GtEq:  return cmp >= 0;
  		}
  		break;
  	}
  
  	case ExactValue_Float: {
  		f64 a = x.value_float;
  		f64 b = y.value_float;
  		switch (op) {
  		case Token_CmpEq: return cmp_f64(a, b) == 0;
  		case Token_NotEq: return cmp_f64(a, b) != 0;
  		case Token_Lt:    return cmp_f64(a, b) <  0;
  		case Token_LtEq:  return cmp_f64(a, b) <= 0;
  		case Token_Gt:    return cmp_f64(a, b) >  0;
  		case Token_GtEq:  return cmp_f64(a, b) >= 0;
  		}
  		break;
  	}
  
  	case ExactValue_Complex: {
  		f64 a = x.value_complex->real;
  		f64 b = x.value_complex->imag;
  		f64 c = y.value_complex->real;
  		f64 d = y.value_complex->imag;
  		switch (op) {
  		case Token_CmpEq: return cmp_f64(a, c) == 0 && cmp_f64(b, d) == 0;
  		case Token_NotEq: return cmp_f64(a, c) != 0 || cmp_f64(b, d) != 0;
  		}
  		break;
  	}
  
  	case ExactValue_String: {
  		String a = x.value_string;
  		String b = y.value_string;
  		// TODO(bill): gb_memcompare is used because the strings are UTF-8
  		switch (op) {
  		case Token_CmpEq: return a == b;
  		case Token_NotEq: return a != b;
  		case Token_Lt:    return a <  b;
  		case Token_LtEq:  return a <= b;
  		case Token_Gt:    return a >  b;
  		case Token_GtEq:  return a >= b;
  		}
  		break;
  	}
  
  	case ExactValue_Typeid:
  		switch (op) {
  		case Token_CmpEq: return are_types_identical(x.value_typeid, y.value_typeid);
  		case Token_NotEq: return !are_types_identical(x.value_typeid, y.value_typeid);
  		}
  		break;
  
  	case ExactValue_Procedure:
  		switch (op) {
  		case Token_CmpEq: return are_types_identical(x.value_typeid, y.value_typeid);
  		case Token_NotEq: return !are_types_identical(x.value_typeid, y.value_typeid);
  		}
  		break;
  	}
  
  	GB_PANIC("Invalid comparison");
  	return false;
  }
  
  Entity *strip_entity_wrapping(Ast *expr);
  Entity *strip_entity_wrapping(Entity *e);
  
  gbString write_expr_to_string(gbString str, Ast *node, bool shorthand);
  
  gbString write_exact_value_to_string(gbString str, ExactValue const &v, isize string_limit=36) {
  	switch (v.kind) {
  	case ExactValue_Invalid:
  		return str;
  	case ExactValue_Bool:
  		return gb_string_appendc(str, v.value_bool ? "true" : "false");
  	case ExactValue_String: {
  		String s = quote_to_ascii(heap_allocator(), v.value_string);
  		string_limit = gb_max(string_limit, 36);
  		if (s.len <= string_limit) {
  			str = gb_string_append_length(str, s.text, s.len);
  		} else {
  			isize n = string_limit/5;
  			str = gb_string_append_length(str, s.text, n);
  			str = gb_string_append_fmt(str, "\"..%lld chars..\"", s.len-(2*n));
  			str = gb_string_append_length(str, s.text+s.len-n, n);
  		}
  		gb_free(heap_allocator(), s.text);
  		return str;
  	}
  	case ExactValue_Integer: {
  		String s = big_int_to_string(heap_allocator(), &v.value_integer);
  		str = gb_string_append_length(str, s.text, s.len);
  		gb_free(heap_allocator(), s.text);
  		return str;
  	}
  	case ExactValue_Float:
  		return gb_string_append_fmt(str, "%f", v.value_float);
  	case ExactValue_Complex:
  		return gb_string_append_fmt(str, "%f+%fi", v.value_complex->real, v.value_complex->imag);
  	case ExactValue_Quaternion:
  		return gb_string_append_fmt(str, "%f+%fi+%fj+%fk", v.value_quaternion->real, v.value_quaternion->imag, v.value_quaternion->jmag, v.value_quaternion->kmag);
  
  	case ExactValue_Pointer:
  		return str;
  	case ExactValue_Compound:
  		return write_expr_to_string(str, v.value_compound, false);
  	case ExactValue_Procedure:
  		return write_expr_to_string(str, v.value_procedure, false);
  	}
  	return str;
  };
  
  gbString exact_value_to_string(ExactValue const &v, isize string_limit=36) {
  	return write_exact_value_to_string(gb_string_make(heap_allocator(), ""), v, string_limit);
  }
  