tomo/types.c

// Logic for handling type_t types
#include <gc/cord.h>
#include <limits.h>
#include <math.h>
#include <signal.h>
#include <stdint.h>
#include <sys/param.h>

#include "cordhelpers.h"
#include "environment.h"
#include "stdlib/integers.h"
#include "stdlib/tables.h"
#include "stdlib/util.h"
#include "types.h"

CORD type_to_cord(type_t *t) {
    if (!t)
        return "(Unknown type)";

    switch (t->tag) {
        case UnknownType: return "???";
        case AbortType: return "Abort";
        case ReturnType: {
            type_t *ret = Match(t, ReturnType)->ret;
            return CORD_all("Return(", ret ? type_to_cord(ret) : "Void", ")");
        }
        case VoidType: return "Void";
        case MemoryType: return "Memory";
        case BoolType: return "Bool";
        case ByteType: return "Byte";
        case CStringType: return "CString";
        case MomentType: return "Moment";
        case TextType: return Match(t, TextType)->lang ? Match(t, TextType)->lang : "Text";
        case BigIntType: return "Int";
        case IntType: return CORD_asprintf("Int%d", Match(t, IntType)->bits);
        case NumType: return Match(t, NumType)->bits == TYPE_NBITS32 ? "Num32" : "Num";
        case ArrayType: {
            auto array = Match(t, ArrayType);
            return CORD_asprintf("[%r]", type_to_cord(array->item_type));
        }
        case TableType: {
            auto table = Match(t, TableType);
            if (table->default_value)
                return CORD_asprintf("{%r=%.*s}", type_to_cord(table->key_type),
                                     table->default_value->end - table->default_value->start, table->default_value->start);
            else
                return CORD_asprintf("{%r:%r}", type_to_cord(table->key_type), type_to_cord(table->value_type));
        }
        case SetType: {
            auto set = Match(t, SetType);
            return CORD_asprintf("{%r}", type_to_cord(set->item_type));
        }
        case ClosureType: {
            return type_to_cord(Match(t, ClosureType)->fn);
        }
        case FunctionType: {
            CORD c = "func(";
            auto fn = Match(t, FunctionType);
            for (arg_t *arg = fn->args; arg; arg = arg->next) {
                c = CORD_cat(c, type_to_cord(arg->type));
                if (arg->next) c = CORD_cat(c, ",");
            }
            if (fn->ret && fn->ret->tag != VoidType)
                c = CORD_all(c, fn->args ? " -> " : "-> ", type_to_cord(fn->ret));
            c = CORD_all(c, ")");
            return c;
        }
        case StructType: {
            auto struct_ = Match(t, StructType);
            return struct_->name;
        }
        case PointerType: {
            auto ptr = Match(t, PointerType);
            CORD sigil = ptr->is_stack ? "&" : "@";
            return CORD_all(sigil, type_to_cord(ptr->pointed));
        }
        case EnumType: {
            auto tagged = Match(t, EnumType);
            return tagged->name;
        }
        case OptionalType: {
            type_t *opt = Match(t, OptionalType)->type;
            if (opt)
                return CORD_all(type_to_cord(opt), "?");
            else
                return "(Unknown optional type)";
        }
        case MutexedType: {
            type_t *opt = Match(t, MutexedType)->type;
            if (opt)
                return CORD_all("mutexed ", type_to_cord(opt));
            else
                return "(Unknown optional type)";
        }
        case TypeInfoType: {
            return CORD_all("Type$info(", Match(t, TypeInfoType)->name, ")");
        }
        case ModuleType: {
            return CORD_all("Module(", Match(t, ModuleType)->name, ")");
        }
        default: {
            raise(SIGABRT);
            return CORD_asprintf("Unknown type: %d", t->tag);
        }
    }
}

PUREFUNC const char *get_type_name(type_t *t)
{
    switch (t->tag) {
    case TextType: return Match(t, TextType)->lang;
    case StructType: return Match(t, StructType)->name;
    case EnumType: return Match(t, EnumType)->name;
    default: return NULL;
    }
}

int printf_pointer_size(const struct printf_info *info, size_t n, int argtypes[n], int sizes[n])
{
    if (n < 1) return -1;
    (void)info;
    argtypes[0] = PA_POINTER;
    sizes[0] = sizeof(void*);
    return 1;
}

int printf_type(FILE *stream, const struct printf_info *info, const void *const args[])
{
    (void)info;
    type_t *t = *(type_t**)args[0];
    if (!t) return fputs("(null)", stream);
    return CORD_put(type_to_cord(t), stream);
}

bool type_eq(type_t *a, type_t *b)
{
    if (a == b) return true;
    if (a->tag != b->tag) return false;
    return (CORD_cmp(type_to_cord(a), type_to_cord(b)) == 0);
}

bool type_is_a(type_t *t, type_t *req)
{
    if (type_eq(t, req)) return true;
    if (req->tag == OptionalType && Match(req, OptionalType)->type)
        return type_is_a(t, Match(req, OptionalType)->type);
    if (t->tag == PointerType && req->tag == PointerType) {
        auto t_ptr = Match(t, PointerType);
        auto req_ptr = Match(req, PointerType);
        if (type_eq(t_ptr->pointed, req_ptr->pointed))
            return (!t_ptr->is_stack && req_ptr->is_stack) || (!t_ptr->is_stack);
    }
    return false;
}

type_t *non_optional(type_t *t)
{
    return t->tag == OptionalType ? Match(t, OptionalType)->type : t;
}

PUREFUNC type_t *value_type(type_t *t)
{
    while (t->tag == PointerType)
        t = Match(t, PointerType)->pointed;
    return t;
}

type_t *type_or_type(type_t *a, type_t *b)
{
    if (!a) return b;
    if (!b) return a;
    if (a->tag == OptionalType && !Match(a, OptionalType)->type)
        return b->tag == OptionalType ? b : Type(OptionalType, b);
    if (b->tag == OptionalType && !Match(b, OptionalType)->type)
        return a->tag == OptionalType ? a : Type(OptionalType, a);
    if (a->tag == ReturnType && b->tag == ReturnType)
        return Type(ReturnType, .ret=type_or_type(Match(a, ReturnType)->ret, Match(b, ReturnType)->ret));
    if (type_is_a(b, a)) return a;
    if (type_is_a(a, b)) return b;
    if (a->tag == AbortType || a->tag == ReturnType) return non_optional(b);
    if (b->tag == AbortType || b->tag == ReturnType) return non_optional(a);
    if ((a->tag == IntType || a->tag == NumType) && (b->tag == IntType || b->tag == NumType)) {
        switch (compare_precision(a, b)) {
        case NUM_PRECISION_EQUAL: case NUM_PRECISION_MORE: return a;
        case NUM_PRECISION_LESS: return b;
        default: return NULL;
        }
        return NULL;
    }
    return NULL;
}

static PUREFUNC INLINE double type_min_magnitude(type_t *t)
{
    switch (t->tag) {
    case BoolType: return (double)false;
    case ByteType: return 0;
    case BigIntType: return -1./0.;
    case IntType: {
        switch (Match(t, IntType)->bits) {
        case TYPE_IBITS8: return (double)INT8_MIN;
        case TYPE_IBITS16: return (double)INT16_MIN;
        case TYPE_IBITS32: return (double)INT32_MIN;
        case TYPE_IBITS64: return (double)INT64_MIN;
        default: errx(1, "Invalid integer bit size");
        }
    }
    case NumType: return -1./0.;
    default: return NAN;
    }
}

static PUREFUNC INLINE double type_max_magnitude(type_t *t)
{
    switch (t->tag) {
    case BoolType: return (double)true;
    case ByteType: return (double)UINT8_MAX;
    case BigIntType: return 1./0.;
    case IntType: {
        switch (Match(t, IntType)->bits) {
        case TYPE_IBITS8: return (double)INT8_MAX;
        case TYPE_IBITS16: return (double)INT16_MAX;
        case TYPE_IBITS32: return (double)INT32_MAX;
        case TYPE_IBITS64: return (double)INT64_MAX;
        default: errx(1, "Invalid integer bit size");
        }
    }
    case NumType: return 1./0.;
    default: return NAN;
    }
}

PUREFUNC precision_cmp_e compare_precision(type_t *a, type_t *b)
{
    if (a->tag == OptionalType && Match(a, OptionalType)->type->tag == NumType)
        a = Match(a, OptionalType)->type;
    if (b->tag == OptionalType && Match(b, OptionalType)->type->tag == NumType)
        b = Match(b, OptionalType)->type;

    if (is_int_type(a) && b->tag == NumType)
        return NUM_PRECISION_LESS;
    else if (a->tag == NumType && is_int_type(b))
        return NUM_PRECISION_MORE;

    double a_min = type_min_magnitude(a),
           b_min = type_min_magnitude(b),
           a_max = type_max_magnitude(a),
           b_max = type_max_magnitude(b);

    if (isnan(a_min) || isnan(b_min) || isnan(a_max) || isnan(b_max))
        return NUM_PRECISION_INCOMPARABLE;
    else if (a_min == b_min && a_max == b_max) return NUM_PRECISION_EQUAL;
    else if (a_min <= b_min && b_max <= a_max) return NUM_PRECISION_MORE;
    else if (b_min <= a_min && a_max <= b_max) return NUM_PRECISION_LESS;
    else return NUM_PRECISION_INCOMPARABLE;
}

PUREFUNC bool has_heap_memory(type_t *t)
{
    switch (t->tag) {
    case ArrayType: return true;
    case TableType: return true;
    case SetType: return true;
    case PointerType: return true;
    case OptionalType: return has_heap_memory(Match(t, OptionalType)->type);
    case MutexedType: return true;
    case BigIntType: return true;
    case StructType: {
        for (arg_t *field = Match(t, StructType)->fields; field; field = field->next) {
            if (has_heap_memory(field->type))
                return true;
        }
        return false;
    }
    case EnumType: {
        for (tag_t *tag = Match(t, EnumType)->tags; tag; tag = tag->next) {
            if (tag->type && has_heap_memory(tag->type))
                return true;
        }
        return false;
    }
    default: return false;
    }
}

PUREFUNC bool has_stack_memory(type_t *t)
{
    switch (t->tag) {
    case PointerType: return Match(t, PointerType)->is_stack;
    case OptionalType: return has_stack_memory(Match(t, OptionalType)->type);
    case MutexedType: return has_stack_memory(Match(t, MutexedType)->type);
    default: return false;
    }
}

PUREFUNC const char *enum_single_value_tag(type_t *enum_type, type_t *t)
{
    const char *found = NULL;
    for (tag_t *tag = Match(enum_type, EnumType)->tags; tag; tag = tag->next) {
        if (tag->type->tag != StructType) continue;
        auto s = Match(tag->type, StructType);
        if (!s->fields || s->fields->next || !s->fields->type)
            continue;

        if (can_promote(t, s->fields->type)) {
            if (found) // Ambiguous case, multiple matches
                return NULL;
            found = tag->name;
            // Continue searching to check for ambiguous cases
        }
    }
    return found;
}

PUREFUNC bool can_promote(type_t *actual, type_t *needed)
{
    if (!actual || !needed)
        return false;

    // No promotion necessary:
    if (type_eq(actual, needed))
        return true;

    if (actual->tag == NumType && needed->tag == IntType)
        return false;

    if (actual->tag == IntType && (needed->tag == NumType || needed->tag == BigIntType))
        return true;

    if (actual->tag == BigIntType && needed->tag == NumType)
        return true;

    if (actual->tag == IntType && needed->tag == IntType) {
        auto cmp = compare_precision(actual, needed);
        return cmp == NUM_PRECISION_EQUAL || cmp == NUM_PRECISION_LESS;
    }

    if (needed->tag == EnumType)
        return (enum_single_value_tag(needed, actual) != NULL);

    // Lang to Text:
    if (actual->tag == TextType && needed->tag == TextType && streq(Match(needed, TextType)->lang, "Text"))
        return true;

    // Text to C String
    if (actual->tag == TextType && !Match(actual, TextType)->lang && needed->tag == CStringType)
        return true;

    // Automatic dereferencing:
    if (actual->tag == PointerType && can_promote(Match(actual, PointerType)->pointed, needed))
        return true;

    if (actual->tag == OptionalType) {
        if (needed->tag == BoolType)
            return true;

        // Ambiguous `none` to concrete optional
        if (Match(actual, OptionalType)->type == NULL)
            return (needed->tag == OptionalType);

        // Optional num -> num
        if (needed->tag == NumType && actual->tag == OptionalType && Match(actual, OptionalType)->type->tag == NumType)
            return can_promote(Match(actual, OptionalType)->type, needed);
    }

    // Optional promotion:
    if (needed->tag == OptionalType && Match(needed, OptionalType)->type != NULL && can_promote(actual, Match(needed, OptionalType)->type))
        return true;

    if (needed->tag == PointerType && actual->tag == PointerType) {
        auto needed_ptr = Match(needed, PointerType);
        auto actual_ptr = Match(actual, PointerType);

        if (actual_ptr->is_stack && !needed_ptr->is_stack)
            // Can't use &x for a function that wants a @Foo or ?Foo
            return false;

        if (needed_ptr->pointed->tag == TableType && actual_ptr->pointed->tag == TableType)
            return can_promote(actual_ptr->pointed, needed_ptr->pointed);
        else if (needed_ptr->pointed->tag != MemoryType && !type_eq(needed_ptr->pointed, actual_ptr->pointed))
            // Can't use @Foo for a function that wants @Baz
            // But you *can* use @Foo for a function that wants @Memory
            return false;
        else
            return true;
    }

    // Cross-promotion between tables with default values and without
    if (needed->tag == TableType && actual->tag == TableType) {
        auto actual_table = Match(actual, TableType);
        auto needed_table = Match(needed, TableType);
        if (type_eq(needed_table->key_type, actual_table->key_type)
            && type_eq(needed_table->value_type, actual_table->value_type))
            return true;
    }

    if (needed->tag == ClosureType && actual->tag == FunctionType)
        return can_promote(actual, Match(needed, ClosureType)->fn);

    if (needed->tag == ClosureType && actual->tag == ClosureType)
        return can_promote(Match(actual, ClosureType)->fn, Match(needed, ClosureType)->fn);

    if (actual->tag == FunctionType && needed->tag == FunctionType) {
        for (arg_t *actual_arg = Match(actual, FunctionType)->args, *needed_arg = Match(needed, FunctionType)->args;
             actual_arg || needed_arg; actual_arg = actual_arg->next, needed_arg = needed_arg->next) {
            if (!actual_arg || !needed_arg) return false;
            if (type_eq(actual_arg->type, needed_arg->type)) continue;
            if (actual_arg->type->tag == PointerType && needed_arg->type->tag == PointerType
                && can_promote(actual_arg->type, needed_arg->type))
                continue;
            return false;
        }
        type_t *actual_ret = Match(actual, FunctionType)->ret;
        if (!actual_ret) actual_ret = Type(VoidType);
        type_t *needed_ret = Match(needed, FunctionType)->ret;
        if (!needed_ret) needed_ret = Type(VoidType);

        return (
            (type_eq(actual_ret, needed_ret))
            || (actual_ret->tag == PointerType && needed_ret->tag == PointerType
                && can_promote(actual_ret, needed_ret)));
    }

    // Set -> Array promotion
    if (needed->tag == ArrayType && actual->tag == SetType
        && type_eq(Match(needed, ArrayType)->item_type, Match(actual, SetType)->item_type))
        return true;

    return false;
}

PUREFUNC bool is_int_type(type_t *t)
{
    return t->tag == IntType || t->tag == BigIntType;
}

PUREFUNC bool is_numeric_type(type_t *t)
{
    return t->tag == IntType || t->tag == BigIntType || t->tag == NumType || t->tag == ByteType;
}

PUREFUNC bool is_packed_data(type_t *t)
{
    if (t->tag == IntType || t->tag == NumType || t->tag == ByteType || t->tag == PointerType || t->tag == BoolType || t->tag == FunctionType) {
        return true;
    } else if (t->tag == StructType) {
        for (arg_t *field = Match(t, StructType)->fields; field; field = field->next) {
            if (!is_packed_data(field->type))
                return false;
        }
        return true;
    } else if (t->tag == EnumType) {
        for (tag_t *tag = Match(t, EnumType)->tags; tag; tag = tag->next) {
            if (!is_packed_data(tag->type))
                return false;
        }
        return true;
    } else {
        return false;
    }
}

PUREFUNC size_t unpadded_struct_size(type_t *t)
{
    arg_t *fields = Match(t, StructType)->fields;
    size_t size = 0;
    size_t bit_offset = 0;
    for (arg_t *field = fields; field; field = field->next) {
        type_t *field_type = field->type;
        if (field_type->tag == BoolType) {
            bit_offset += 1;
            if (bit_offset >= 8) {
                size += 1;
                bit_offset = 0;
            }
        } else {
            if (bit_offset > 0) {
                size += 1;
                bit_offset = 0;
            }
            size_t align = type_align(field_type);
            if (align > 1 && size % align > 0)
                size += align - (size % align); // Padding
            size += type_size(field_type);
        }
    }
    if (bit_offset > 0) {
        size += 1;
        bit_offset = 0;
    }
    return size;
}

PUREFUNC size_t type_size(type_t *t)
{
    if (t == THREAD_TYPE) return sizeof(pthread_t*);
    if (t == PATH_TYPE) return sizeof(Path_t);
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wswitch-default"
    switch (t->tag) {
    case UnknownType: case AbortType: case ReturnType: case VoidType: return 0;
    case MemoryType: errx(1, "Memory has undefined type size");
    case BoolType: return sizeof(bool);
    case ByteType: return sizeof(uint8_t);
    case CStringType: return sizeof(char*);
    case MomentType: return sizeof(Moment_t);
    case BigIntType: return sizeof(Int_t);
    case IntType: {
        switch (Match(t, IntType)->bits) {
        case TYPE_IBITS64: return sizeof(int64_t);
        case TYPE_IBITS32: return sizeof(int32_t);
        case TYPE_IBITS16: return sizeof(int16_t);
        case TYPE_IBITS8: return sizeof(int8_t);
        default: errx(1, "Invalid integer bit size");
        }
    }
    case NumType: return Match(t, NumType)->bits == TYPE_NBITS64 ? sizeof(double) : sizeof(float);
    case TextType: return sizeof(Text_t);
    case ArrayType: return sizeof(Array_t);
    case SetType: return sizeof(Table_t);
    case TableType: return sizeof(Table_t);
    case FunctionType: return sizeof(void*);
    case ClosureType: return sizeof(struct {void *fn, *userdata;});
    case PointerType: return sizeof(void*);
    case MutexedType: return sizeof(MutexedData_t);
    case OptionalType: {
        type_t *nonnull = Match(t, OptionalType)->type;
        switch (nonnull->tag) {
        case IntType:
            switch (Match(nonnull, IntType)->bits) {
            case TYPE_IBITS64: return sizeof(OptionalInt64_t);
            case TYPE_IBITS32: return sizeof(OptionalInt32_t);
            case TYPE_IBITS16: return sizeof(OptionalInt16_t);
            case TYPE_IBITS8: return sizeof(OptionalInt8_t);
            default: errx(1, "Invalid integer bit size");
            }
        case StructType: {
            size_t size = unpadded_struct_size(nonnull);
            size += sizeof(bool); // is_null flag
            size_t align = type_align(nonnull);
            if (align > 0 && (size % align) > 0)
                size = (size + align) - (size % align);
            return size;
        }
        default: return type_size(nonnull);
        }
    }
    case StructType: {
        size_t size = unpadded_struct_size(t);
        size_t align = type_align(t);
        if (size > 0 && align > 0 && (size % align) > 0)
            size = (size + align) - (size % align);
        return size;
    }
    case EnumType: {
        size_t max_align = 0;
        size_t max_size = 0;
        for (tag_t *tag = Match(t, EnumType)->tags; tag; tag = tag->next) {
            size_t align = type_align(tag->type);
            if (align > max_align) max_align = align;
            size_t size = type_size(tag->type);
            if (size > max_size) max_size = size;
        }
        size_t size = sizeof(UnknownType); // generic enum
        if (max_align > 1 && size % max_align > 0) // Padding before first union field
            size += max_align - (size % max_align);
        size += max_size;
        size_t align = MAX(__alignof__(UnknownType), max_align);
        if (size % align > 0) // Padding after union
            size += align - (size % align);
        return size;
    }
    case TypeInfoType: return sizeof(TypeInfo_t);
    case ModuleType: return 0;
    }
#pragma GCC diagnostic pop
    errx(1, "This should not be reachable");
}

PUREFUNC size_t type_align(type_t *t)
{
    if (t == THREAD_TYPE) return __alignof__(pthread_t*);
    if (t == PATH_TYPE) return __alignof__(Path_t);
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wswitch-default"
    switch (t->tag) {
    case UnknownType: case AbortType: case ReturnType: case VoidType: return 0;
    case MemoryType: errx(1, "Memory has undefined type alignment");
    case BoolType: return __alignof__(bool);
    case ByteType: return __alignof__(uint8_t);
    case CStringType: return __alignof__(char*);
    case MomentType: return __alignof__(Moment_t);
    case BigIntType: return __alignof__(Int_t);
    case IntType: {
        switch (Match(t, IntType)->bits) {
        case TYPE_IBITS64: return __alignof__(int64_t);
        case TYPE_IBITS32: return __alignof__(int32_t);
        case TYPE_IBITS16: return __alignof__(int16_t);
        case TYPE_IBITS8: return __alignof__(int8_t);
        default: return 0;
        }
    }
    case NumType: return Match(t, NumType)->bits == TYPE_NBITS64 ? __alignof__(double) : __alignof__(float);
    case TextType: return __alignof__(Text_t);
    case SetType: return __alignof__(Table_t);
    case ArrayType: return __alignof__(Array_t);
    case TableType: return __alignof__(Table_t);
    case FunctionType: return __alignof__(void*);
    case ClosureType: return __alignof__(struct {void *fn, *userdata;});
    case PointerType: return __alignof__(void*);
    case MutexedType: return __alignof__(MutexedData_t);
    case OptionalType: {
        type_t *nonnull = Match(t, OptionalType)->type;
        switch (nonnull->tag) {
        case IntType:
            switch (Match(nonnull, IntType)->bits) {
            case TYPE_IBITS64: return __alignof__(OptionalInt64_t);
            case TYPE_IBITS32: return __alignof__(OptionalInt32_t);
            case TYPE_IBITS16: return __alignof__(OptionalInt16_t);
            case TYPE_IBITS8: return __alignof__(OptionalInt8_t);
            default: errx(1, "Invalid integer bit size");
            }
        case StructType: return MAX(1, type_align(nonnull));
        default: return type_align(nonnull);
        }
    }
    case StructType: {
        arg_t *fields = Match(t, StructType)->fields;
        size_t align = t->tag == StructType ? 0 : sizeof(void*);
        for (arg_t *field = fields; field; field = field->next) {
            size_t field_align = type_align(field->type);
            if (field_align > align) align = field_align;
        }
        return align;
    }
    case EnumType: {
        size_t align = __alignof__(UnknownType);
        for (tag_t *tag = Match(t, EnumType)->tags; tag; tag = tag->next) {
            size_t tag_align = type_align(tag->type);
            if (tag_align > align) align = tag_align;
        }
        return align;
    }
    case TypeInfoType: return __alignof__(TypeInfo_t);
    case ModuleType: return 0;
    }
#pragma GCC diagnostic pop
    errx(1, "This should not be reachable");
}

type_t *get_field_type(type_t *t, const char *field_name)
{
    t = value_type(t);
    switch (t->tag) {
    case PointerType:
        return get_field_type(Match(t, PointerType)->pointed, field_name);
    case TextType: {
        if (Match(t, TextType)->lang && streq(field_name, "text"))
            return TEXT_TYPE;
        else if (streq(field_name, "length")) return INT_TYPE;
        return NULL;
    }
    case StructType: {
        auto struct_t = Match(t, StructType);
        for (arg_t *field = struct_t->fields; field; field = field->next) {
            if (streq(field->name, field_name))
                return field->type;
        }
        return NULL;
    }
    case EnumType: {
        auto e = Match(t, EnumType);
        for (tag_t *tag = e->tags; tag; tag = tag->next) {
            if (streq(field_name, tag->name))
                return Type(BoolType);
        }
        return NULL;
    }
    case SetType: {
        if (streq(field_name, "length"))
            return INT_TYPE;
        else if (streq(field_name, "items"))
            return Type(ArrayType, .item_type=Match(t, SetType)->item_type);
        return NULL;
    }
    case TableType: {
        if (streq(field_name, "length"))
            return INT_TYPE;
        else if (streq(field_name, "keys"))
            return Type(ArrayType, Match(t, TableType)->key_type);
        else if (streq(field_name, "values"))
            return Type(ArrayType, Match(t, TableType)->value_type);
        else if (streq(field_name, "fallback"))
            return Type(OptionalType, .type=t);
        return NULL;
    }
    case ArrayType: {
        if (streq(field_name, "length")) return INT_TYPE;
        return NULL;
    }
    case MomentType: {
        if (streq(field_name, "seconds")) return Type(IntType, .bits=TYPE_IBITS64);
        else if (streq(field_name, "microseconds")) return Type(IntType, .bits=TYPE_IBITS64);
        return NULL;
    }
    default: return NULL;
    }
}

PUREFUNC type_t *get_iterated_type(type_t *t)
{
    type_t *iter_value_t = value_type(t);
    switch (iter_value_t->tag) {
    case BigIntType: case IntType: return iter_value_t; break;
    case ArrayType: return Match(iter_value_t, ArrayType)->item_type; break;
    case SetType: return Match(iter_value_t, SetType)->item_type; break;
    case TableType: return NULL;
    case FunctionType: case ClosureType: {
        // Iterator function
        auto fn = iter_value_t->tag == ClosureType ?
            Match(Match(iter_value_t, ClosureType)->fn, FunctionType) : Match(iter_value_t, FunctionType);
        if (fn->args || fn->ret->tag != OptionalType)
            return NULL;
        return Match(fn->ret, OptionalType)->type;
    }
    default: return NULL;
    }
}

// vim: ts=4 sw=0 et cino=L2,l1,(0,W4,m1,\:0