apfl/src/context.c

#include <assert.h>
#include <stdarg.h>
#include <stdlib.h>
#include <string.h>
#include <setjmp.h>

#include "apfl.h"
#include "alloc.h"
#include "compile.h"
#include "context.h"
#include "gc.h"
#include "globals.h"
#include "hashmap.h"
#include "resizable.h"
#include "strings.h"
#include "value.h"

static bool try_push_const_string(apfl_ctx ctx, const char *string);
static bool current_stack_move_to_top(apfl_ctx, apfl_stackidx);
static struct apfl_string *new_copied_string(struct gc *, struct apfl_string_view);

APFL_NORETURN static void
panic(apfl_ctx ctx, enum apfl_result result)
{
    (void)ctx;
    (void)result;
    fprintf(stderr, "panic!\n");
    // TODO: more details
    abort();
}

struct protected_errcallback_data {
    void *opaque_outer;
    void (*errcallback)(apfl_ctx, void *);
};

void
protected_errcallback(apfl_ctx ctx, void *opaque)
{
    struct protected_errcallback_data *data = opaque;
    data->errcallback(ctx, data->opaque_outer);
}

enum apfl_result
apfl_do_protected(
    apfl_ctx ctx,
    void (*callback)(apfl_ctx, void *),
    void *opaque,
    void (*errcallback)(apfl_ctx, void *)
) {
    struct error_handler *prev_handler = ctx->error_handler;

    size_t callstack_len = ctx->call_stack.len;
    size_t tmproots = apfl_gc_tmproots_begin(&ctx->gc);

    struct error_handler handler;
    ctx->error_handler = &handler;

    enum apfl_result result = APFL_RESULT_OK;
    int rv = setjmp(handler.jump);
    if (rv == 0) {
        callback(ctx, opaque);
    } else {
        result = (enum apfl_result)(rv - RESULT_OFF_FOR_LONGJMP);
        assert(result != APFL_RESULT_OK);

        bool with_error_on_stack = APFL_RESULT_ERR;

        if (with_error_on_stack && errcallback != NULL) {
            struct protected_errcallback_data data = {
                .opaque_outer = opaque,
                .errcallback = errcallback,
            };
            switch (apfl_do_protected(ctx, protected_errcallback, &data, NULL)) {
            case APFL_RESULT_OK:
                break;
            case APFL_RESULT_ERR:
                result = APFL_RESULT_ERRERR;
                with_error_on_stack = false;
                break;
            case APFL_RESULT_ERRERR:
                result = APFL_RESULT_ERRERR;
                with_error_on_stack = false;
                break;
            case APFL_RESULT_ERR_ALLOC:
                result = APFL_RESULT_ERR_ALLOC;
                with_error_on_stack = false;
                break;
            }
        }

        struct apfl_value err;
        if (with_error_on_stack && !apfl_stack_pop(ctx, &err, -1)) {
            result = APFL_RESULT_ERRERR;
            with_error_on_stack = false;
        }

        apfl_gc_tmproots_restore(&ctx->gc, tmproots);
        tmproots = apfl_gc_tmproots_begin(&ctx->gc);
        if (with_error_on_stack && !apfl_value_add_as_tmproot(&ctx->gc, err)) {
            result = APFL_RESULT_ERRERR;
            with_error_on_stack = false;
        }

        assert(callstack_len <= ctx->call_stack.cap);
        for (size_t i = callstack_len; i < ctx->call_stack.len; i++) {
            apfl_call_stack_entry_deinit(ctx->gc.allocator, &ctx->call_stack.items[i]);
        }

        assert(
            // Shrinking should not fail
            apfl_resizable_resize(
                ctx->gc.allocator,
                sizeof(struct call_stack_entry),
                (void **)&ctx->call_stack.items,
                &ctx->call_stack.len,
                &ctx->call_stack.cap,
                callstack_len
            )
        );

        if (with_error_on_stack && !apfl_stack_push(ctx, err)) {
            result = APFL_RESULT_ERRERR;
            with_error_on_stack = false;
        }

        apfl_gc_tmproots_restore(&ctx->gc, tmproots);
    }

    ctx->error_handler = prev_handler;

    return result;
}

struct call_protected_data {
    apfl_stackidx func;
    apfl_stackidx args;
};

static void
call_protected_cb(apfl_ctx ctx, void *opaque)
{
    struct call_protected_data *data = opaque;
    apfl_call(ctx, data->func, data->args);
}

enum apfl_result
apfl_call_protected(apfl_ctx ctx, apfl_stackidx func, apfl_stackidx args)
{
    struct call_protected_data data = {
        .func = func,
        .args = args,
    };
    return apfl_do_protected(ctx, call_protected_cb, &data, NULL);
}

APFL_NORETURN static void
raise_error(apfl_ctx ctx, enum apfl_result type)
{
    assert(type != APFL_RESULT_OK);

    if (ctx->error_handler != NULL) {
        longjmp(ctx->error_handler->jump, (int)type + RESULT_OFF_FOR_LONGJMP);
    }

    if (ctx->panic_callback != NULL) {
        ctx->panic_callback(ctx, ctx->panic_callback_data, type);
    }

    panic(ctx, type);
}

APFL_NORETURN void
apfl_raise_error(apfl_ctx ctx, apfl_stackidx idx)
{
    if (!current_stack_move_to_top(ctx, idx)) {
        raise_error(ctx, APFL_RESULT_ERRERR);
    }
    raise_error(ctx, APFL_RESULT_ERR);
}

APFL_NORETURN void
apfl_raise_const_error(apfl_ctx ctx, const char *message)
{
    if (!try_push_const_string(ctx, message)) {
        raise_error(ctx, APFL_RESULT_ERRERR);
    }
    raise_error(ctx, APFL_RESULT_ERR);
}

APFL_NORETURN void
apfl_raise_alloc_error(apfl_ctx ctx)
{
    raise_error(ctx, APFL_RESULT_ERR_ALLOC);
}

APFL_NORETURN void
apfl_raise_invalid_stackidx(apfl_ctx ctx)
{
    apfl_raise_const_error(ctx, apfl_messages.invalid_stack_index);
}

APFL_NORETURN void
apfl_raise_error_object(apfl_ctx ctx, struct apfl_error error)
{
    if (error.type == APFL_ERR_MALLOC_FAILED) {
        apfl_raise_alloc_error(ctx);
    }

    const char *const_str = apfl_error_as_const_string(error);
    if (const_str != NULL) {
        apfl_raise_const_error(ctx, const_str);
    }

    struct apfl_string string;
    if (!apfl_error_as_string(error, ctx->gc.allocator, &string)) {
        apfl_raise_alloc_error(ctx);
    }

    if (!apfl_move_string_onto_stack(ctx, string)) {
        apfl_raise_alloc_error(ctx);
    }

    apfl_raise_error(ctx, -1);
}

struct errorfmt_data {
    va_list ap;
    apfl_ctx ctx;
};

static bool
errorfmt_str(void *opaque, struct apfl_io_writer w, struct apfl_string_view arg)
{
    struct errorfmt_data *data = opaque;

    struct apfl_string_view sv;
    if (apfl_string_eq(arg, "c")) {
        char *cstr = va_arg(data->ap, char *);
        sv = apfl_string_view_from(cstr);
    } else {
        sv = va_arg(data->ap, struct apfl_string_view);
    }

    return apfl_io_write_string_view(w, sv);
}

static bool
errorfmt_type(void *opaque, struct apfl_io_writer w, struct apfl_string_view arg)
{
    struct errorfmt_data *data = opaque;

    enum apfl_value_type type;
    if (apfl_string_eq(arg, "stack")) {
        apfl_stackidx i = va_arg(data->ap, apfl_stackidx);
        struct apfl_value val;
        if (!apfl_stack_get(data->ctx, &val, i)) {
            FMT_TRY(apfl_io_write_string(w, "{stack:type => invalid stack index}"));
            return true;
        }
        type = apfl_value_type_to_abstract_type(val.type);
    } else if (apfl_string_eq(arg, "value")) {
        struct apfl_value val = va_arg(data->ap, struct apfl_value);
        type = apfl_value_type_to_abstract_type(val.type);
    } else {
        type = va_arg(data->ap, enum apfl_value_type);
    }

    return apfl_io_write_string_view(w, apfl_string_view_from(apfl_type_name(type)));
}

static const struct format_spec errorfmt_specs[] = {
    {"string", errorfmt_str},
    {"type", errorfmt_type},
    {NULL, NULL},
};

APFL_NORETURN void
apfl_raise_errorfmt(apfl_ctx ctx, const char *fmt, ...)
{
    struct errorfmt_data data = {
        .ctx = ctx,
    };
    va_start(data.ap, fmt);

    struct apfl_string_builder sb = apfl_string_builder_init(ctx->gc.allocator);
    struct apfl_io_writer w = apfl_io_string_writer(&sb);

    bool result = apfl_abstract_format(&data, errorfmt_specs, w, apfl_string_view_from(fmt));
    va_end(data.ap);

    if (!result) {
        apfl_string_builder_deinit(&sb);
        apfl_raise_alloc_error(ctx);
    }

    struct apfl_string string = apfl_string_builder_move_string(&sb);
    apfl_string_builder_deinit(&sb);

    if (!apfl_move_string_onto_stack(ctx, string)) {
        apfl_raise_alloc_error(ctx);
    }

    apfl_raise_error(ctx, -1);
}

void
apfl_ctx_set_panic_callback(apfl_ctx ctx, apfl_panic_callback cb, void *opaque)
{
    ctx->panic_callback = cb;
    ctx->panic_callback_data = opaque;
}

struct stack
apfl_stack_new(void)
{
    return (struct stack) {
        .items = NULL,
        .len = 0,
        .cap = 0,
    };
}

static struct stack *
current_value_stack(apfl_ctx ctx)
{
    struct call_stack_entry *csentry = apfl_call_stack_cur_entry(ctx);
    return csentry != NULL
        ? &csentry->stack
        : &ctx->toplevel_stack;
}

void
apfl_stack_must_push(apfl_ctx ctx, struct apfl_value value)
{
    if (!apfl_stack_push(ctx, value)) {
        apfl_raise_alloc_error(ctx);
    }
}

bool
apfl_stack_push(apfl_ctx ctx, struct apfl_value value)
{
    struct stack *stack = current_value_stack(ctx);

    return apfl_resizable_append(
        ctx->gc.allocator,
        sizeof(struct apfl_value),
        (void **)&stack->items,
        &stack->len,
        &stack->cap,
        &value,
        1
    );
}

static bool
stack_check_index(struct stack *stack, apfl_stackidx *index)
{
    if (*index < 0) {
        if ((size_t)-*index > stack->len) {
            return false;
        }
        *index = stack->len + *index;
    } else if ((size_t)*index >= stack->len) {
        return false;
    }

    assert(0 <= *index && (size_t)*index < stack->len);

    return true;
}

bool
apfl_stack_check_index(apfl_ctx ctx, apfl_stackidx *index)
{
    return stack_check_index(current_value_stack(ctx), index);
}

bool
apfl_stack_has_index(apfl_ctx ctx, apfl_stackidx index)
{
    return apfl_stack_check_index(ctx, &index);
}

static int
cmp_stackidx(const void *_a, const void *_b)
{
    const apfl_stackidx *a = _a;
    const apfl_stackidx *b = _b;
    return *a - *b;
}

bool
apfl_stack_drop_multi(apfl_ctx ctx, size_t count, apfl_stackidx *indices)
{
    struct stack *stack = current_value_stack(ctx);

    for (size_t i = 0; i < count; i++) {
        if (!stack_check_index(stack, &indices[i])) {
            return false;
        }
    }

    qsort(indices, count, sizeof(apfl_stackidx), cmp_stackidx);

    for (size_t i = count; i-- > 0; ) {
        // Will not fail, as we've already checked the indices
        assert(apfl_resizable_cut_without_resize(
            sizeof(struct apfl_value),
            (void **)&stack->items,
            &stack->len,
            indices[i],
            1
        ));
    }

    // TODO: Shrink stack

    return true;
}

bool
apfl_stack_pop(apfl_ctx ctx, struct apfl_value *value, apfl_stackidx index)
{
    struct stack *stack = current_value_stack(ctx);

    if (!stack_check_index(stack, &index)) {
        return false;
    }

    *value = stack->items[index];

    assert(apfl_resizable_splice(
        ctx->gc.allocator,
        sizeof(struct apfl_value),
        (void **)&stack->items,
        &stack->len,
        &stack->cap,
        index,
        1,
        NULL,
        0
    ));

    return true;
}

struct apfl_value
apfl_stack_must_pop(apfl_ctx ctx, apfl_stackidx index)
{
    struct apfl_value value;
    if (!apfl_stack_pop(ctx, &value, index)) {
        apfl_raise_invalid_stackidx(ctx);
    }
    return value;
}

static struct apfl_value *
stack_get_pointer(apfl_ctx ctx, apfl_stackidx index)
{
    struct stack *stack = current_value_stack(ctx);

    if (!stack_check_index(stack, &index)) {
        return NULL;
    }

    return &stack->items[index];
}

static bool
stack_get_and_adjust_index(struct stack *stack, struct apfl_value *value, apfl_stackidx *index)
{
    if (!stack_check_index(stack, index)) {
        return false;
    }

    *value = stack->items[*index];

    return true;
}

static bool
current_stack_get_and_adjust_index(apfl_ctx ctx, struct apfl_value *value, apfl_stackidx *index)
{
    return stack_get_and_adjust_index(current_value_stack(ctx), value, index);
}

bool
apfl_stack_get(apfl_ctx ctx, struct apfl_value *value, apfl_stackidx index)
{
    return current_stack_get_and_adjust_index(ctx, value, &index);
}

struct apfl_value
apfl_stack_must_get(apfl_ctx ctx, apfl_stackidx index)
{
    struct apfl_value value;
    if (!apfl_stack_get(ctx, &value, index)) {
        apfl_raise_invalid_stackidx(ctx);
    }
    return value;
}

struct apfl_value *
apfl_stack_push_placeholder(apfl_ctx ctx)
{
    if (!apfl_stack_push(ctx, (struct apfl_value) {.type = VALUE_NIL})) {
        return NULL;
    }

    return stack_get_pointer(ctx, -1);
}

bool
apfl_move_string_onto_stack(apfl_ctx ctx, struct apfl_string string)
{
    struct apfl_value *value = apfl_stack_push_placeholder(ctx);
    if (value == NULL) {
        return false;
    }

    if ((value->string = apfl_string_move_into_new_gc_string(&ctx->gc, &string)) == NULL) {
        return false;
    }

    value->type = VALUE_STRING;

    return true;
}

bool
apfl_stack_drop(apfl_ctx ctx, apfl_stackidx index)
{
    struct apfl_value value;
    return apfl_stack_pop(ctx, &value, index);
}

void
apfl_drop(apfl_ctx ctx, apfl_stackidx index)
{
    if (!apfl_stack_drop(ctx, index)) {
        apfl_raise_invalid_stackidx(ctx);
    }
}

bool
current_stack_multi_move_to_top(apfl_ctx ctx, size_t count, apfl_stackidx *indices)
{
    struct stack *stack = current_value_stack(ctx);

    for (size_t i = 0; i < count; i++) {
        if (!stack_check_index(stack, &indices[i])) {
            return false;
        }
    }

    for (size_t i = 0; i < count; i++) {
        // If we're here, index is an absolute address and is guaranteed to be < len
        assert(indices[i] >= 0);
        size_t absindex = (size_t)indices[i];
        assert(stack->len >= absindex+1);

        struct apfl_value val = stack->items[absindex];

        memmove(
            &stack->items[absindex],
            &stack->items[absindex + 1],
            sizeof(struct apfl_value) * (stack->len - absindex - 1)
        );
        stack->items[stack->len-1] = val;

        for (size_t j = i + 1; j < count; j++) {
            if (indices[j] >= indices[i]) {
                indices[j]--;
            }
        }
    }

    return true;
}

static bool
current_stack_move_to_top(apfl_ctx ctx, apfl_stackidx index)
{
    return current_stack_multi_move_to_top(ctx, 1, &index);
}

void
apfl_move_to_top_of_stack(apfl_ctx ctx, apfl_stackidx index)
{
    if (!current_stack_move_to_top(ctx, index)) {
        apfl_raise_invalid_stackidx(ctx);
    }
}

void
apfl_multi_move_to_top_of_stack(apfl_ctx ctx, size_t count, apfl_stackidx *indices)
{
    if (!current_stack_multi_move_to_top(ctx, count, indices)) {
        apfl_raise_invalid_stackidx(ctx);
    }
}

void
apfl_copy(apfl_ctx ctx, apfl_stackidx index)
{
    struct apfl_value value = apfl_stack_must_get(ctx, index);
    apfl_stack_must_push(ctx, apfl_value_set_cow_flag(value));
}

void
apfl_stack_clear(apfl_ctx ctx)
{
    struct stack *stack = current_value_stack(ctx);
    stack->len = 0;
}

static void
stack_traverse(struct stack stack, gc_visitor visitor, void *opaque)
{
    for (size_t i = 0; i < stack.len; i++) {
        apfl_value_visit_gc_object(stack.items[i], visitor, opaque);
    }
}

static void
visit_nullable_scope(struct scope *scope, gc_visitor visitor, void *opaque)
{
    if (scope != NULL) {
        visitor(opaque, GC_OBJECT_FROM(scope, GC_TYPE_SCOPE));
    }
}

static void
visit_scopes(struct scopes scopes, gc_visitor visitor, void *opaque)
{
    visit_nullable_scope(scopes.local, visitor, opaque);
    visit_nullable_scope(scopes.closure, visitor, opaque);
}

static void
visit_matcher_stack(struct matcher_stack matcher_stack, gc_visitor visitor, void *opaque)
{
    for (size_t i = 0; i < matcher_stack.len; i++) {
        visitor(
            opaque,
            GC_OBJECT_FROM(matcher_stack.items[i], GC_TYPE_MATCHER)
        );
    }
}

static void
visit_func_cse(struct func_call_stack_entry cse, gc_visitor visitor, void *opaque)
{
    visitor(
        opaque,
        GC_OBJECT_FROM(cse.instructions, GC_TYPE_INSTRUCTIONS)
    );

    visit_scopes(cse.scopes, visitor, opaque);
    visit_matcher_stack(cse.matcher_stack, visitor, opaque);
}

static void
visit_cfunc_cse(struct cfunc_call_stack_entry cse, gc_visitor visitor, void *opaque)
{
    visitor(
        opaque,
        GC_OBJECT_FROM(cse.func, GC_TYPE_CFUNC)
    );
}

static void
visit_matcher_cse(struct matcher_call_stack_entry cse, gc_visitor visitor, void* opaque)
{
    visitor(
        opaque,
        GC_OBJECT_FROM(cse.matcher, GC_TYPE_MATCHER)
    );
    visit_scopes(cse.scopes, visitor, opaque);
    for (size_t i = 0; i < cse.capture_count; i++) {
        apfl_value_visit_gc_object(cse.captures[i], visitor, opaque);
        visitor(
            opaque,
            GC_OBJECT_FROM(cse.transfers[i].var, GC_TYPE_STRING)
        );
    }
}

static void
visit_func_dispatch_cse(struct func_dispatch_call_stack_entry cse, gc_visitor visitor, void *opaque)
{
    visitor(
        opaque,
        GC_OBJECT_FROM(cse.function, GC_TYPE_FUNC)
    );
    visit_scopes(cse.scopes, visitor, opaque);
}

static void
gc_traverse_call_stack_entry(struct call_stack_entry cse, gc_visitor visitor, void *opaque)
{
    stack_traverse(cse.stack, visitor, opaque);

    switch (cse.type) {
    case APFL_CSE_FUNCTION:
        visit_func_cse(cse.func, visitor, opaque);
        break;
    case APFL_CSE_CFUNCTION:
        visit_cfunc_cse(cse.cfunc, visitor, opaque);
        break;
    case APFL_CSE_MATCHER:
        visit_matcher_cse(cse.matcher, visitor, opaque);
        break;
    case APFL_CSE_FUNCTION_DISPATCH:
        visit_func_dispatch_cse(cse.func_dispatch, visitor, opaque);
        break;
    }
}

static void
get_roots(void *own_opaque, gc_visitor visitor, void *visitor_opaque)
{
    apfl_ctx ctx = own_opaque;

    if (ctx->globals != NULL) {
        visitor(visitor_opaque, GC_OBJECT_FROM(ctx->globals, GC_TYPE_SCOPE));
    }

    stack_traverse(ctx->toplevel_stack, visitor, visitor_opaque);

    for (size_t i = 0; i < ctx->call_stack.len; i++) {
        gc_traverse_call_stack_entry(ctx->call_stack.items[i], visitor, visitor_opaque);
    }

    for (size_t i = 0; i < ctx->iterative_runners.len; i++) {
        apfl_iterative_runner_visit_gc_objects(ctx->iterative_runners.items[i], visitor, visitor_opaque);
    }
}

static struct call_stack
call_stack_new(void)
{
    return (struct call_stack) {
        .items = NULL,
        .len = 0,
        .cap = 0,
    };
}

static void
deinit_stack(struct apfl_allocator allocator, struct stack *stack)
{
    FREE_LIST(allocator, stack->items, stack->cap);
    *stack = apfl_stack_new();
}

static void
func_call_stack_entry_deinit(struct apfl_allocator allocator, struct func_call_stack_entry *cse)
{
    FREE_LIST(allocator, cse->matcher_stack.items, cse->matcher_stack.cap);
}

void
apfl_matcher_call_stack_entry_deinit(struct apfl_allocator allocator, struct matcher_call_stack_entry *cse)
{
    FREE_LIST(allocator, cse->captures, cse->capture_count);
    cse->captures = NULL;
    FREE_LIST(allocator, cse->transfers, cse->capture_count);
    cse->transfers = NULL;
    FREE_LIST(allocator, cse->matcher_state_stack, cse->matcher_state_stack_cap);
    cse->matcher_state_stack = NULL;
}

void
apfl_call_stack_entry_deinit(struct apfl_allocator allocator, struct call_stack_entry *entry)
{
    deinit_stack(allocator, &entry->stack);

    switch (entry->type) {
    case APFL_CSE_FUNCTION:
        func_call_stack_entry_deinit(allocator, &entry->func);
        break;
    case APFL_CSE_CFUNCTION:
    case APFL_CSE_FUNCTION_DISPATCH:
        break;
    case APFL_CSE_MATCHER:
        apfl_matcher_call_stack_entry_deinit(allocator, &entry->matcher);
        break;
    }
}

struct call_stack_entry *
apfl_call_stack_cur_entry(apfl_ctx ctx)
{
    return ctx->call_stack.len == 0
        ? NULL
        : &ctx->call_stack.items[ctx->call_stack.len - 1];
}

static struct iterative_runners_list
iterative_runners_list_new(void)
{
    return (struct iterative_runners_list) {
        .items = NULL,
        .len = 0,
        .cap = 0,
    };
}

static bool
init_globals(apfl_ctx ctx)
{
    struct gc *gc = &ctx->gc;

    size_t tmproots = apfl_gc_tmproots_begin(gc);

    for (
        const struct global_def *global = apfl_globals();
        global->name != NULL && global->func != NULL;
        global++
    ) {
        struct cfunction *cfunc = apfl_cfunc_new(gc, global->func, 0);
        if (cfunc == NULL) {
            goto error;
        }

        if (!apfl_gc_tmproot_add(gc, GC_OBJECT_FROM(cfunc, GC_TYPE_CFUNC))) {
            goto error;
        }

        struct apfl_string *name = new_copied_string(gc, apfl_string_view_from(global->name));
        if (name == NULL) {
            goto error;
        }

        if (!apfl_gc_tmproot_add(gc, GC_OBJECT_FROM(name, GC_TYPE_STRING))) {
            goto error;
        }

        // TODO: There should also be an API for setting the name of a cfunc
        cfunc->name = name;

        if (!apfl_scope_set(gc, ctx->globals, name, (struct apfl_value) {
            .type = VALUE_CFUNC,
            .cfunc = cfunc,
        })) {
            goto error;
        }

        apfl_gc_tmproots_restore(gc, tmproots);
    }

    return true;

error:
    apfl_gc_tmproots_restore(gc, tmproots);
    return false;
}

apfl_ctx
apfl_ctx_new(struct apfl_config config)
{
    apfl_ctx ctx = ALLOC_OBJ(config.allocator, struct apfl_ctx_data);
    if (ctx == NULL) {
        return NULL;
    }

    // It's important that we initialize all these before initializing the
    // garbage collector, otherwise it might try to follow invalid pointers.
    ctx->error_handler = NULL;
    ctx->panic_callback = NULL;
    ctx->panic_callback_data = NULL;
    ctx->toplevel_stack = apfl_stack_new();
    ctx->call_stack = call_stack_new();
    ctx->globals = NULL;
    ctx->iterative_runners = iterative_runners_list_new();

    apfl_gc_init(&ctx->gc, config.allocator, get_roots, ctx);

    if ((ctx->globals = apfl_scope_new(&ctx->gc)) == NULL) {
        goto error;
    }

    ctx->output_writer = config.output_writer;

    if (!init_globals(ctx)) {
        goto error;
    }

    return ctx;

error:
    apfl_ctx_destroy(ctx);
    return NULL;
}

void
apfl_ctx_destroy(apfl_ctx ctx)
{
    if (ctx == NULL) {
        return;
    }

    deinit_stack(ctx->gc.allocator, &ctx->toplevel_stack);
    ctx->toplevel_stack = apfl_stack_new();

    DEINIT_CAP_LIST(
        ctx->gc.allocator,
        ctx->call_stack.items,
        ctx->call_stack.len,
        ctx->call_stack.cap,
        apfl_call_stack_entry_deinit
    );

    ctx->call_stack = call_stack_new();

    FREE_LIST(ctx->gc.allocator, ctx->iterative_runners.items, ctx->iterative_runners.cap);
    ctx->iterative_runners = iterative_runners_list_new();

    struct apfl_allocator base_allocator = ctx->gc.base_allocator;

    apfl_gc_full(&ctx->gc);
    apfl_gc_deinit(&ctx->gc);

    FREE_OBJ(base_allocator, ctx);
}

static bool
find_iterative_runner(apfl_ctx ctx, apfl_iterative_runner runner, size_t *index)
{
    // It should be very uncommon that there are a lot of iterative runners
    // existing on the same apfl_ctx at the same time, so a linear scan should
    // be good enough :)
    for (size_t i = 0; i < ctx->iterative_runners.len; i++) {
        if (ctx->iterative_runners.items[i] == runner) {
            if (index != NULL) {
                *index = i;
            }
            return true;
        }
    }
    return false;
}

struct iterative_runner_tmproot_data {
    struct gc *gc;
    bool ok;
};

static void
ctx_register_iterative_runner_tmproot(void *opaque, struct gc_object *object)
{
    struct iterative_runner_tmproot_data *data = opaque;
    if (!data->ok) {
        return;
    }
    data->ok = apfl_gc_tmproot_add(data->gc, object);
}

static bool
ctx_register_iterative_runner_inner(apfl_ctx ctx, apfl_iterative_runner runner)
{
    struct iterative_runner_tmproot_data data = {
        .gc = &ctx->gc,
        .ok = true
    };
    apfl_iterative_runner_visit_gc_objects(runner, ctx_register_iterative_runner_tmproot, &data);

    if (!data.ok) {
        return false;
    }

    if (find_iterative_runner(ctx, runner, NULL)) {
        return true;
    }

    return apfl_resizable_append(
        ctx->gc.allocator,
        sizeof(apfl_iterative_runner),
        (void **)&ctx->iterative_runners.items,
        &ctx->iterative_runners.len,
        &ctx->iterative_runners.cap,
        &runner,
        1
    );
}

bool
apfl_ctx_register_iterative_runner(apfl_ctx ctx, apfl_iterative_runner runner)
{
    size_t tmproots = apfl_gc_tmproots_begin(&ctx->gc);
    bool out = ctx_register_iterative_runner_inner(ctx, runner);
    apfl_gc_tmproots_restore(&ctx->gc, tmproots);
    return out;
}

void
apfl_ctx_unregister_iterative_runner(apfl_ctx ctx, apfl_iterative_runner runner)
{
    size_t i;
    if (!find_iterative_runner(ctx, runner, &i)) {
        return;
    }

    assert(
        // We're only removing elements, the buffer should not grow,
        // therefore there should be no allocation errors
        apfl_resizable_splice(
            ctx->gc.allocator,
            sizeof(apfl_iterative_runner),
            (void **)&ctx->iterative_runners.items,
            &ctx->iterative_runners.len,
            &ctx->iterative_runners.cap,
            i,
            1,
            NULL,
            0
        )
    );
}

#define CREATE_GC_OBJECT_VALUE_ON_STACK(ctx, TYPE, MEMB, NEW)    \
    struct apfl_value *value = apfl_stack_push_placeholder(ctx); \
    if (value == NULL) {                                         \
        apfl_raise_alloc_error(ctx);                             \
    }                                                            \
                                                                 \
    struct apfl_value new_value = {.type = TYPE};                \
    if ((new_value.MEMB = NEW) == NULL) {                        \
        assert(apfl_stack_drop(ctx, -1));                        \
        apfl_raise_alloc_error(ctx);                             \
    }                                                            \
                                                                 \
    *value = new_value;

void
apfl_push_nil(apfl_ctx ctx)
{
    apfl_stack_must_push(ctx, (struct apfl_value) {
        .type = VALUE_NIL,
    });
}

void
apfl_push_bool(apfl_ctx ctx, bool b)
{
    apfl_stack_must_push(ctx, (struct apfl_value) {
        .type = VALUE_BOOLEAN,
        .boolean = b,
    });
}

void
apfl_push_number(apfl_ctx ctx, apfl_number num)
{
    apfl_stack_must_push(ctx, (struct apfl_value) {
        .type = VALUE_NUMBER,
        .number = num,
    });
}

static struct apfl_string *
new_copied_string(struct gc *gc, struct apfl_string_view sv)
{
    struct apfl_string s = apfl_string_blank();
    if (!apfl_string_copy(gc->allocator, &s, sv)) {
        return NULL;
    }

    struct apfl_string *out = apfl_string_move_into_new_gc_string(gc, &s);
    if (out == NULL) {
        apfl_string_deinit(gc->allocator, &s);
        return NULL;
    }

    return out;
}

void
apfl_push_string_view_copy(apfl_ctx ctx, struct apfl_string_view sv)
{
    CREATE_GC_OBJECT_VALUE_ON_STACK(
        ctx,
        VALUE_STRING,
        string,
        new_copied_string(&ctx->gc, sv)
    )
}

static bool
try_push_const_string(apfl_ctx ctx, const char *string)
{
    return apfl_stack_push(ctx, (struct apfl_value) {
        .type = VALUE_CONST_STRING,
        .const_string = apfl_string_view_from(string),
    });
}

void
apfl_push_const_string(apfl_ctx ctx, const char *string)
{
    if (!try_push_const_string(ctx, string)) {
        apfl_raise_alloc_error(ctx);
    }
}

void
apfl_list_create(apfl_ctx ctx, size_t initial_cap)
{
    CREATE_GC_OBJECT_VALUE_ON_STACK(
        ctx,
        VALUE_LIST,
        list,
        apfl_list_new(&ctx->gc, initial_cap)
    )
}

void
apfl_list_append(apfl_ctx ctx, apfl_stackidx list_index, apfl_stackidx value_index)
{
    struct apfl_value *list_val = stack_get_pointer(ctx, list_index);
    if (list_val == NULL) {
        apfl_raise_invalid_stackidx(ctx);
    }

    if (list_val->type != VALUE_LIST) {
        apfl_raise_errorfmt(
            ctx,
            "Can not append to value of type {value:type}, expected list",
            *list_val
        );
    }

    struct apfl_value value = apfl_stack_must_get(ctx, value_index);

    if (!apfl_list_splice(
        &ctx->gc,
        &list_val->list,
        list_val->list->len,
        0,
        &value,
        1
    )) {
        assert(apfl_stack_drop(ctx, value_index));
        apfl_raise_alloc_error(ctx);
    }

    assert(apfl_stack_drop(ctx, value_index));
}

void
apfl_list_append_list(apfl_ctx ctx, apfl_stackidx dst_index, apfl_stackidx src_index)
{
    struct apfl_value *dst_val = stack_get_pointer(ctx, dst_index);
    if (dst_val == NULL) {
        apfl_raise_invalid_stackidx(ctx);
    }

    if (dst_val->type != VALUE_LIST) {
        apfl_raise_const_error(ctx, apfl_messages.not_a_list);
    }

    struct apfl_value src_val = apfl_stack_must_get(ctx, src_index);

    if (src_val.type != VALUE_LIST) {
        assert(apfl_stack_drop(ctx, src_index));
        apfl_raise_const_error(ctx, apfl_messages.not_a_list);
    }

    if (!apfl_list_splice(
        &ctx->gc,
        &dst_val->list,
        dst_val->list->len,
        0,
        src_val.list->items,
        src_val.list->len
    )) {
        apfl_raise_alloc_error(ctx);
    }

    assert(apfl_stack_drop(ctx, src_index));
}

void
apfl_dict_create(apfl_ctx ctx)
{
    CREATE_GC_OBJECT_VALUE_ON_STACK(
        ctx,
        VALUE_DICT,
        dict,
        apfl_dict_new(&ctx->gc)
    )
}

void
apfl_dict_set(
    apfl_ctx ctx,
    apfl_stackidx dict_index,
    apfl_stackidx k_index,
    apfl_stackidx v_index
) {
    struct apfl_value k;
    struct apfl_value v;
    struct apfl_value *dict_value;

    if (
        !apfl_stack_get(ctx, &k, k_index)
        || !apfl_stack_get(ctx, &v, v_index)
        || (dict_value = stack_get_pointer(ctx, dict_index)) == NULL
    ) {
        apfl_raise_invalid_stackidx(ctx);
    }

    if (dict_value->type != VALUE_DICT) {
        assert(apfl_stack_drop_multi(ctx, 2, (apfl_stackidx[]){k_index, v_index}));
        apfl_raise_const_error(ctx, apfl_messages.not_a_dict);
    }

    if (!apfl_dict_set_raw(&ctx->gc, &dict_value->dict, k, v)) {
        assert(apfl_stack_drop_multi(ctx, 2, (apfl_stackidx[]){k_index, v_index}));
        apfl_raise_alloc_error(ctx);
    }

    assert(apfl_stack_drop_multi(ctx, 2, (apfl_stackidx[]){k_index, v_index}));
}

bool
apfl_get_member_if_exists(
    apfl_ctx ctx,
    apfl_stackidx container_index,
    apfl_stackidx k_index
) {
    struct apfl_value container;
    struct apfl_value k;
    if (
        !current_stack_get_and_adjust_index(ctx, &container, &container_index)
        || !current_stack_get_and_adjust_index(ctx, &k, &k_index)
    ) {
        apfl_raise_invalid_stackidx(ctx);
    }

    struct apfl_value *value = apfl_stack_push_placeholder(ctx);
    if (value == NULL) {
        assert(apfl_stack_drop_multi(ctx, 2, (apfl_stackidx[]){k_index, container_index}));
        apfl_raise_alloc_error(ctx);
    }

    enum get_item_result result = apfl_value_get_item(container, k, value);
    if (result != GET_ITEM_OK) {
        assert(apfl_stack_drop(ctx, -1)); // Drop the placeholder
    }

    assert(apfl_stack_drop_multi(ctx, 2, (apfl_stackidx[]){k_index, container_index}));

    switch (result) {
    case GET_ITEM_OK:
        return true;
    case GET_ITEM_KEY_DOESNT_EXIST:
        return false;
    case GET_ITEM_NOT_A_CONTAINER:
        apfl_raise_errorfmt(
            ctx,
            "Can not get member of value of type {value:type}, not a container",
            container
        );
        break;
    case GET_ITEM_WRONG_KEY_TYPE:
        apfl_raise_errorfmt(
            ctx,
            "Value of type {value:type} is not a valid key for container type {value:type}",
            k,
            container
        );
        break;
    }

    assert(false);
    return false;
}

void
apfl_get_member(
    apfl_ctx ctx,
    apfl_stackidx container_index,
    apfl_stackidx k_index
) {
    if (!apfl_get_member_if_exists(ctx, container_index, k_index)) {
        apfl_raise_const_error(ctx, apfl_messages.key_doesnt_exist);
    }
}

void
apfl_get_list_member_by_index(
    apfl_ctx ctx,
    apfl_stackidx list_index,
    size_t index
) {
    struct apfl_value list = apfl_stack_must_get(ctx, list_index);

    if (list.type != VALUE_LIST) {
        apfl_raise_const_error(ctx, apfl_messages.not_a_list);
    }

    if (index >= list.list->len) {
        apfl_raise_const_error(ctx, apfl_messages.key_doesnt_exist);
    }

    struct apfl_value *value = apfl_stack_push_placeholder(ctx);
    if (value == NULL) {
        apfl_raise_alloc_error(ctx);
    }

    *value = apfl_value_set_cow_flag(list.list->items[index]);
}

void
apfl_set_list_member_by_index(
    apfl_ctx ctx,
    apfl_stackidx list_index,
    size_t index_in_list,
    apfl_stackidx value_index
) {
    struct apfl_value *list = stack_get_pointer(ctx, list_index);
    if (list == NULL) {
        apfl_raise_invalid_stackidx(ctx);
    }

    if (list->type != VALUE_LIST) {
        apfl_raise_const_error(ctx, apfl_messages.not_a_list);
    }

    if (index_in_list >= list->list->len) {
        apfl_raise_const_error(ctx, apfl_messages.key_doesnt_exist);
    }

    struct apfl_value value = apfl_stack_must_get(ctx, value_index);

    if (!apfl_list_splice(
        &ctx->gc,
        &list->list,
        index_in_list,
        1,
        &value,
        1
    )) {
        apfl_raise_alloc_error(ctx);
    }

    apfl_drop(ctx, value_index);
}

size_t
apfl_len(apfl_ctx ctx, apfl_stackidx index)
{
    struct apfl_value value = apfl_stack_must_get(ctx, index);
    switch (value.type) {
    case VALUE_NIL:
    case VALUE_BOOLEAN:
    case VALUE_NUMBER:
    case VALUE_FUNC:
    case VALUE_CFUNC:
    case VALUE_USERDATA:
    case VALUE_NATIVE_OBJECT:
        apfl_raise_errorfmt(
            ctx,
            "Can not get length of value of type {value:type}",
            value
        );
        return 0;
    case VALUE_STRING:
        return value.string->len;
    case VALUE_CONST_STRING:
        return value.const_string.len;
    case VALUE_LIST:
        return apfl_list_len(value.list);
    case VALUE_DICT:
        return apfl_dict_len(value.dict);
    }

    assert(false);
    return 0;
}

static bool
get_string_view_of_value(struct apfl_string_view *sv, struct apfl_value value)
{
    switch (value.type) {
    case VALUE_NIL:
    case VALUE_BOOLEAN:
    case VALUE_NUMBER:
    case VALUE_FUNC:
    case VALUE_CFUNC:
    case VALUE_USERDATA:
    case VALUE_LIST:
    case VALUE_DICT:
    case VALUE_NATIVE_OBJECT:
        return false;
    case VALUE_STRING:
        *sv = apfl_string_view_from(*value.string);
        return true;
    case VALUE_CONST_STRING:
        *sv = value.const_string;
        return true;
    }

    assert(false);
    return false;
}

struct apfl_string_view
apfl_get_string(apfl_ctx ctx, apfl_stackidx index)
{
    struct apfl_string_view sv;
    if (!get_string_view_of_value(&sv, apfl_stack_must_get(ctx, index))) {
        apfl_raise_errorfmt(ctx, "Expected string, got {stack:type}", index);
    }
    return sv;
}

enum apfl_value_type
apfl_get_type(apfl_ctx ctx, apfl_stackidx index)
{
    struct apfl_value value = apfl_stack_must_get(ctx, index);
    return apfl_value_type_to_abstract_type(value.type);
}

void
apfl_tostring(apfl_ctx ctx, apfl_stackidx index)
{
    apfl_move_to_top_of_stack(ctx, index);
    struct apfl_value value = apfl_stack_must_get(ctx, -1);
    if (apfl_value_type_to_abstract_type(value.type) == APFL_VALUE_STRING) {
        return;
    }

    struct apfl_string_builder sb = apfl_string_builder_init(ctx->gc.allocator);
    if (!apfl_value_format(value, apfl_io_string_writer(&sb))) {
        apfl_string_builder_deinit(&sb);
        apfl_stack_drop(ctx, -1);
        apfl_raise_alloc_error(ctx);
    }

    struct apfl_string str = apfl_string_builder_move_string(&sb);
    apfl_string_builder_deinit(&sb);
    if (!apfl_move_string_onto_stack(ctx, str)) {
        apfl_string_deinit(ctx->gc.allocator, &str);
        apfl_stack_drop(ctx, -1);
        apfl_raise_alloc_error(ctx);
    }

    apfl_stack_drop(ctx, -2); // Drop original value
}

struct apfl_string *
apfl_to_dynamic_string(apfl_ctx ctx, apfl_stackidx index)
{
    apfl_tostring(ctx, index);
    struct apfl_value value = apfl_stack_must_get(ctx, -1);
    if (value.type == VALUE_STRING) {
        return value.string;
    }

    assert(value.type == VALUE_CONST_STRING /* apfl_tostring results in either VALUE_STRING or VALUE_CONST_STRING */);

    apfl_push_string_view_copy(ctx, value.const_string);
    value = apfl_stack_must_get(ctx, -1);
    apfl_drop(ctx, -2);

    return value.string;
}

void
apfl_join_strings(apfl_ctx ctx, apfl_stackidx glue, apfl_stackidx parts)
{
    apfl_multi_move_to_top_of_stack(ctx, 2, (apfl_stackidx[]){parts, glue});
    parts = -2;
    glue = -1;

    if (apfl_get_type(ctx, parts) != APFL_VALUE_LIST) {
        apfl_raise_const_error(ctx, apfl_messages.not_a_list);
    }
    size_t parts_len = apfl_len(ctx, parts);

    apfl_tostring(ctx, glue);
    struct apfl_string_view glue_sv = apfl_get_string(ctx, glue);

    size_t total_length = 0;

    for (size_t i = 0; i < parts_len; i++) {
        // Convert values to strings, if necessary
        apfl_get_list_member_by_index(ctx, parts, i);
        if (apfl_get_type(ctx, -1) == APFL_VALUE_STRING) {
            total_length += apfl_get_string(ctx, -1).len;
            apfl_drop(ctx, -1);
        } else {
            apfl_tostring(ctx, -1);
            total_length += apfl_get_string(ctx, -1).len;
            apfl_set_list_member_by_index(ctx, -3, i, -1);
        }

        if (i > 0) {
            total_length += glue_sv.len;
        }
    }

    struct apfl_string_builder sb = apfl_string_builder_init(ctx->gc.allocator);
    if (!apfl_string_builder_prealloc(&sb, total_length)) {
        goto error;
    }

    for (size_t i = 0; i < parts_len; i++) {
        if (i > 0) {
            if (!apfl_string_builder_append(&sb, glue_sv)) {
                goto error;
            }
        }

        apfl_get_list_member_by_index(ctx, parts, i);

        if (!apfl_string_builder_append(&sb, apfl_get_string(ctx, -1))) {
            goto error;
        }

        apfl_drop(ctx, -1);
    }


    struct apfl_string str = apfl_string_builder_move_string(&sb);
    apfl_string_builder_deinit(&sb);
    if (!apfl_move_string_onto_stack(ctx, str)) {
        apfl_string_deinit(ctx->gc.allocator, &str);
        goto error;
    }

    // Drop the glue and list from the stack
    apfl_drop(ctx, -2);
    apfl_drop(ctx, -2);
    return;

error:
    // Drop the glue and list from the stack
    apfl_drop(ctx, -1);
    apfl_drop(ctx, -1);
    apfl_raise_alloc_error(ctx);
}

void
apfl_concat_strings(apfl_ctx ctx, apfl_stackidx a, apfl_stackidx b)
{
    apfl_multi_move_to_top_of_stack(ctx, 2, (apfl_stackidx[]){a, b});
    apfl_tostring(ctx, -2);
    apfl_tostring(ctx, -2);

    struct apfl_string_view sv_a = apfl_get_string(ctx, -2);
    struct apfl_string_view sv_b = apfl_get_string(ctx, -1);

    struct apfl_string_builder sb = apfl_string_builder_init(ctx->gc.allocator);
    if (!apfl_string_builder_prealloc(&sb, sv_a.len + sv_b.len)) {
        goto error;
    }

    if (
        !apfl_string_builder_append(&sb, sv_a)
        || !apfl_string_builder_append(&sb, sv_b)
    ) {
        goto error;
    }

    struct apfl_string str = apfl_string_builder_move_string(&sb);
    apfl_string_builder_deinit(&sb);
    if (!apfl_move_string_onto_stack(ctx, str)) {
        apfl_string_deinit(ctx->gc.allocator, &str);
        goto error;
    }

    apfl_drop(ctx, -2);
    apfl_drop(ctx, -2);
    return;

error:
    apfl_drop(ctx, -1);
    apfl_drop(ctx, -1);
    apfl_raise_alloc_error(ctx);
}

bool
apfl_is_truthy(apfl_ctx ctx, apfl_stackidx index)
{
    struct apfl_value value = apfl_stack_must_pop(ctx, index);
    switch (value.type) {
    case VALUE_NIL:
        return false;
    case VALUE_BOOLEAN:
        return value.boolean;
    default:
        return true;
    }
}

apfl_number
apfl_get_number(apfl_ctx ctx, apfl_stackidx index)
{
    struct apfl_value value = apfl_stack_must_pop(ctx, index);
    if (value.type == VALUE_NUMBER) {
        return value.number;
    }
    apfl_raise_errorfmt(ctx, "Expected number, got {value:type}", value);
}

bool
apfl_eq(apfl_ctx ctx, apfl_stackidx _a, apfl_stackidx _b)
{
    struct apfl_value a = apfl_stack_must_get(ctx, _a);
    struct apfl_value b = apfl_stack_must_get(ctx, _b);

    bool eq = apfl_value_eq(a, b);
    assert(apfl_stack_drop_multi(ctx, 2, (apfl_stackidx[]){_a, _b}));
    return eq;
}

int
apfl_cmp(apfl_ctx ctx, apfl_stackidx _a, apfl_stackidx _b)
{
    struct apfl_value a = apfl_stack_must_get(ctx, _a);
    struct apfl_value b = apfl_stack_must_get(ctx, _b);

    enum comparison_result result = apfl_value_cmp(a, b);
    assert(apfl_stack_drop_multi(ctx, 2, (apfl_stackidx[]){_a, _b}));

    switch (result) {
    case CMP_LT:
        return -1;
    case CMP_EQ:
        return 0;
    case CMP_GT:
        return 1;
    case CMP_UNCOMPARABLE:
        apfl_raise_errorfmt(ctx, "Values of type {value:type} can not be compared", a);
    case CMP_INCOMPATIBLE_TYPES:
        apfl_raise_errorfmt(ctx, "Can not compare values of incompatible types {value:type} and {value:type}", a, b);
    }

    assert(false);
    return 0;
}

static struct scope *
closure_scope_for_func_inner(apfl_ctx ctx, struct scopes scopes)
{
    struct scope *out = apfl_scope_new(&ctx->gc);
    if (out == NULL) {
        return NULL;
    }

    if (!apfl_gc_tmproot_add(&ctx->gc, GC_OBJECT_FROM(out, GC_TYPE_SCOPE))) {
        return NULL;
    }

    // The order is important here: by merging the local scope last, we make
    // sure a variable from the current scope shadows a variable from the
    // closure scope

    if (scopes.closure != NULL) {
        if (!apfl_scope_merge_into(out, scopes.closure)) {
            return NULL;
        }
    }

    if (scopes.local != NULL) {
        if (!apfl_scope_merge_into(out, scopes.local)) {
            return NULL;
        }
    }

    return out;
}

struct scope *
apfl_closure_scope_for_func(apfl_ctx ctx, struct scopes scopes)
{
    size_t tmproots = apfl_gc_tmproots_begin(&ctx->gc);
    struct scope *out = closure_scope_for_func_inner(ctx, scopes);
    apfl_gc_tmproots_restore(&ctx->gc, tmproots);
    return out;
}

void
apfl_push_cfunc(apfl_ctx ctx, apfl_cfunc cfunc, size_t nslots)
{
    CREATE_GC_OBJECT_VALUE_ON_STACK(
        ctx,
        VALUE_CFUNC,
        cfunc,
        apfl_cfunc_new(&ctx->gc, cfunc, nslots)
    )
}

static APFL_NORETURN void
raise_no_cfunc(apfl_ctx ctx)
{
    apfl_raise_const_error(ctx, apfl_messages.not_a_c_function);
}

static struct cfunction *
must_get_cfunc(apfl_ctx ctx, apfl_stackidx idx)
{
    struct apfl_value value = apfl_stack_must_get(ctx, idx);
    if (value.type != VALUE_CFUNC) {
        raise_no_cfunc(ctx);
    }
    return value.cfunc;
}

static struct cfunction *
must_get_cfunc_self(apfl_ctx ctx)
{
    struct call_stack_entry *entry = apfl_call_stack_cur_entry(ctx);
    if (entry == NULL) {
        raise_no_cfunc(ctx);
    }

    if (entry->type != APFL_CSE_CFUNCTION) {
        raise_no_cfunc(ctx);
    }

    return entry->cfunc.func;
}

static struct apfl_value **
cfunc_getslotvar(apfl_ctx ctx, struct cfunction *cfunction, apfl_slotidx slot)
{
    if (slot >= cfunction->slots_len) {
        apfl_raise_const_error(ctx, apfl_messages.invalid_slotidx);
    }
    return &cfunction->slots[slot];
}

static void
cfunc_getslot(apfl_ctx ctx, struct cfunction *cfunction, apfl_slotidx slot)
{
    struct apfl_value **var = cfunc_getslotvar(ctx, cfunction, slot);
    if (*var == NULL) {
        apfl_push_nil(ctx);
        return;
    }

    // The value is now in the slot and on the stack. We need to set the COW
    // flag so a mutation of one copy doesn't affect the other one.
    apfl_stack_must_push(ctx, apfl_value_set_cow_flag(**var));
}

void
apfl_cfunc_getslot(apfl_ctx ctx, apfl_stackidx cfunc, apfl_slotidx slot)
{
    cfunc_getslot(ctx, must_get_cfunc(ctx, cfunc), slot);
}

void
apfl_cfunc_self_getslot(apfl_ctx ctx, apfl_slotidx slot)
{
    cfunc_getslot(ctx, must_get_cfunc_self(ctx), slot);
}

static void
cfunc_setslot(apfl_ctx ctx, struct cfunction *cfunction, apfl_slotidx slot, apfl_stackidx value)
{
    struct apfl_value **var = cfunc_getslotvar(ctx, cfunction, slot);
    if (*var == NULL) {
        *var = apfl_gc_new_var(&ctx->gc);
        if (*var == NULL) {
            apfl_raise_alloc_error(ctx);
        }

        **var = (struct apfl_value) { .type = VALUE_NIL };
    }

    **var = apfl_stack_must_pop(ctx, value);
}

void
apfl_cfunc_setslot(apfl_ctx ctx, apfl_stackidx cfunc, apfl_slotidx slot, apfl_stackidx value)
{
    cfunc_setslot(ctx, must_get_cfunc(ctx, cfunc), slot, value);
}

void
apfl_cfunc_self_setslot(apfl_ctx ctx, apfl_slotidx slot, apfl_stackidx value)
{
    cfunc_setslot(ctx, must_get_cfunc_self(ctx), slot, value);
}

void
apfl_push_userdata(apfl_ctx ctx, void *userdata)
{
    apfl_stack_must_push(ctx, (struct apfl_value) {
        .type = VALUE_USERDATA,
        .userdata = userdata,
    });
}

void *apfl_get_userdata(apfl_ctx ctx, apfl_stackidx index)
{
    struct apfl_value value = apfl_stack_must_pop(ctx, index);
    if (value.type != VALUE_USERDATA) {
        apfl_raise_const_error(ctx, apfl_messages.wrong_type);
    }
    return value.userdata;
}

void *
apfl_push_native_object(apfl_ctx ctx, const struct apfl_native_object_type *type)
{
    CREATE_GC_OBJECT_VALUE_ON_STACK(
        ctx,
        VALUE_NATIVE_OBJECT,
        native_object,
        apfl_native_object_new(&ctx->gc, type)
    )

    return apfl_get_native_object(ctx, type, -1);
}

void *
apfl_get_native_object(apfl_ctx ctx, const struct apfl_native_object_type *type, apfl_stackidx index)
{
    struct apfl_value value = apfl_stack_must_get(ctx, index);
    if (value.type != VALUE_NATIVE_OBJECT || value.native_object->type != type) {
        apfl_raise_const_error(ctx, apfl_messages.wrong_type);
    }
    return value.native_object->memory;
}

struct apfl_io_writer apfl_get_output_writer(apfl_ctx ctx)
{
    return ctx->output_writer;
}

static bool
init_values_list(struct apfl_allocator allocator, struct apfl_value **list, size_t len)
{
    if (len == 0) {
        return true;
    }

    if ((*list = ALLOC_LIST(allocator, struct apfl_value, len)) == NULL) {
        return false;
    }

    for (size_t i = 0; i < len; i++) {
        (*list)[i] = (struct apfl_value) { .type = VALUE_NIL };
    }
    return true;
}

struct matcher *
apfl_matcher_new(struct gc *gc, struct matcher_instruction_list *milist)
{
    struct matcher matcher = {
        .instructions = milist,
        .value_count = 0,
        .values = NULL,
    };

    if (!init_values_list(gc->allocator, &matcher.values, milist->value_count)) {
        goto error;
    }
    matcher.value_count = milist->value_count;

    struct matcher *gc_matcher = apfl_gc_new_matcher(gc);
    if (gc_matcher == NULL) {
        goto error;
    }

    *gc_matcher = matcher;

    return gc_matcher;

error:
    apfl_matcher_deinit(gc->allocator, &matcher);
    return NULL;
}

void
apfl_matcher_deinit(struct apfl_allocator allocator, struct matcher *matcher)
{
    FREE_LIST(allocator, matcher->values, matcher->value_count);
}

void
apfl_gc_matcher_traverse(struct matcher *matcher, gc_visitor visitor, void *opaque)
{
    visitor(opaque, GC_OBJECT_FROM(matcher->instructions, GC_TYPE_MATCHER_INSTRUCTIONS));

    for (size_t i = 0; i < matcher->instructions->value_count; i++) {
        apfl_value_visit_gc_object(matcher->values[i], visitor, opaque);
    }
}

size_t
apfl_call_stack_depth(apfl_ctx ctx)
{
    return ctx->call_stack.len;
}

static struct apfl_string_view
get_string_view_or_empty(struct apfl_string *s)
{
    return s == NULL
        ? (struct apfl_string_view) { .len = 0, .bytes = NULL, }
        : apfl_string_view_from(*s);
}

struct apfl_call_stack_entry_info
apfl_call_stack_inspect(apfl_ctx ctx, size_t n)
{
    if (n >= ctx->call_stack.len) {
        apfl_raise_const_error(ctx, apfl_messages.invalid_call_stack_index);
    }

    struct call_stack_entry *cse = &ctx->call_stack.items[ctx->call_stack.len - n - 1];

    struct apfl_call_stack_entry_info info = {
        .type = cse->type,
        .name = (struct apfl_string_view) { .len = 0, .bytes = NULL, },
        .filename = (struct apfl_string_view) { .len = 0, .bytes = NULL, },
        .toplevel = false,
    };

    switch (cse->type) {
    case APFL_CSE_FUNCTION:
        info.line_current = cse->func.execution_line;
        info.filename = get_string_view_or_empty(cse->func.instructions->filename);
        if (cse->func.function == NULL) {
            info.toplevel = true;
        } else {
            info.line_defined = cse->func.instructions->line;
            info.subfunction_index = cse->func.subfunction_index;

            struct apfl_string_view sv;
            if (apfl_func_get_name(cse->func.function, &sv)) {
                info.name = sv;
            }
        }
        break;
    case APFL_CSE_CFUNCTION:
        info.name = get_string_view_or_empty(cse->cfunc.func->name);
        break;
    case APFL_CSE_FUNCTION_DISPATCH: {
        struct apfl_string_view sv;
        if (apfl_func_get_name(cse->func_dispatch.function, &sv)) {
            info.name = sv;
        }
        info.line_defined = cse->func_dispatch.function->line_defined;
        info.filename = get_string_view_or_empty(cse->func_dispatch.function->filename);
        break;
    }
    case APFL_CSE_MATCHER:
        break;
    }

    return info;
}

static bool
format_defined_at(
    struct apfl_io_writer w,
    struct apfl_call_stack_entry_info info,
    struct apfl_string_view *filename
) {
    FMT_TRY(apfl_io_write_string(w, "defined in "));
    if (filename != NULL && filename->len > 0) {
        FMT_TRY(apfl_io_write_string(w, "file "));
        FMT_TRY(apfl_io_write_string(w, *filename));
        FMT_TRY(apfl_io_write_string(w, ", "));
    }
    FMT_TRY(apfl_io_write_string(w, "line "));
    FMT_TRY(apfl_format_put_int(w, info.line_defined));
    return true;
}

bool
apfl_call_stack_entry_info_format(struct apfl_io_writer w, struct apfl_call_stack_entry_info info)
{
    switch (info.type) {
    case APFL_CSE_FUNCTION:
        if (info.filename.len > 0) {
            FMT_TRY(apfl_io_write_string(w, "File "));
            FMT_TRY(apfl_io_write_string(w, info.filename));
            FMT_TRY(apfl_io_write_string(w, ", "));
        }
        FMT_TRY(apfl_io_write_string(w, "Line "));
        FMT_TRY(apfl_format_put_int(w, info.line_current));
        FMT_TRY(apfl_io_write_string(w, ", "));

        if (info.toplevel) {
            FMT_TRY(apfl_io_write_string(w, "toplevel "));
        } else if (info.name.len == 0) {
            FMT_TRY(apfl_io_write_string(w, "anonymous function (subfunction "));
            FMT_TRY(apfl_format_put_int(w, (int)info.subfunction_index));
            FMT_TRY(apfl_io_write_string(w, "; "));
            FMT_TRY(format_defined_at(w, info, NULL));
            FMT_TRY(apfl_io_write_string(w, ")"));
        } else {
            FMT_TRY(apfl_io_write_string(w, "function "));
            FMT_TRY(apfl_io_write_string(w, info.name));
            FMT_TRY(apfl_io_write_string(w, " (subfunction "));
            FMT_TRY(apfl_format_put_int(w, (int)info.subfunction_index));
            FMT_TRY(apfl_io_write_string(w, "; "));
            FMT_TRY(format_defined_at(w, info, NULL));
            FMT_TRY(apfl_io_write_string(w, ")"));
        }
        break;
    case APFL_CSE_CFUNCTION:
        if (info.name.len == 0) {
            FMT_TRY(apfl_io_write_string(w, "Anonymous native function"));
        } else {
            FMT_TRY(apfl_io_write_string(w, "Native function "));
            FMT_TRY(apfl_io_write_string(w, info.name));
        }
        break;
    case APFL_CSE_FUNCTION_DISPATCH:
        FMT_TRY(apfl_io_write_string(w, "Dispatch for "));
        if (info.name.len == 0) {
            FMT_TRY(apfl_io_write_string(w, "anonymous function ("));
        } else {
            FMT_TRY(apfl_io_write_string(w, "function "));
            FMT_TRY(apfl_io_write_string(w, info.name));
            FMT_TRY(apfl_io_write_string(w, "("));
        }
        FMT_TRY(format_defined_at(w, info, &info.filename));
        FMT_TRY(apfl_io_write_string(w, ")"));
        break;
    case APFL_CSE_MATCHER:
        FMT_TRY(apfl_io_write_string(w, "Matcher"));
        break;
    }

    return true;
}

static struct instruction_list *
setup_function_for_load_inner(apfl_ctx ctx, struct apfl_string *filename)
{
    struct apfl_value *func_value = apfl_stack_push_placeholder(ctx);
    if (func_value == NULL) {
        return NULL;
    }

    if ((func_value->func = apfl_func_new(&ctx->gc, 1, NULL, 1, filename)) == NULL) {
        apfl_drop(ctx, -1);
        return NULL;
    }
    func_value->type = VALUE_FUNC;

    struct instruction_list *ilist = apfl_instructions_new(&ctx->gc, 1, filename);
    if (
        ilist == NULL
        || !apfl_gc_tmproot_add(&ctx->gc, GC_OBJECT_FROM(ilist, GC_TYPE_INSTRUCTIONS))
    ) {
        return NULL;
    }

    struct matcher_instruction_list *milist = apfl_matcher_instructions_new(&ctx->gc);
    if (
        milist == NULL
        || !apfl_gc_tmproot_add(&ctx->gc, GC_OBJECT_FROM(milist, GC_TYPE_MATCHER_INSTRUCTIONS))
    ) {
        return NULL;
    }

    if (!apfl_resizable_append(
        ctx->gc.allocator,
        sizeof(union matcher_instruction_or_arg),
        (void **)&milist->instructions,
        &milist->len,
        &milist->cap,
        &(union matcher_instruction_or_arg[]) {
            {.instruction = MATCHER_IGNORE},
        },
        1
    )) {
        return NULL;
    }

    struct matcher *matcher = apfl_matcher_new(&ctx->gc, milist);
    if (
        matcher == NULL
        || !apfl_gc_tmproot_add(&ctx->gc, GC_OBJECT_FROM(matcher, GC_TYPE_MATCHER))
    ) {
        apfl_drop(ctx, -1);
        return NULL;
    }

    if (!apfl_func_add_subfunc(func_value->func, ilist, matcher)) {
        apfl_drop(ctx, -1);
        return NULL;
    }

    return ilist;
}

static struct instruction_list *
setup_function_for_load(apfl_ctx ctx, struct apfl_string *filename)
{
    size_t tmproots = apfl_gc_tmproots_begin(&ctx->gc);
    struct instruction_list *out = setup_function_for_load_inner(ctx, filename);
    apfl_gc_tmproots_restore(&ctx->gc, tmproots);
    return out;
}

void
apfl_load(apfl_ctx ctx, struct apfl_source_reader reader, apfl_stackidx name)
{
    struct apfl_string *filename = apfl_to_dynamic_string(ctx, name);

    apfl_tokenizer_ptr tokenizer = apfl_tokenizer_new(ctx->gc.allocator, reader);
    if (tokenizer == NULL) {
        apfl_raise_alloc_error(ctx);
    }

    apfl_parser_ptr parser = apfl_parser_new(
        ctx->gc.allocator,
        apfl_tokenizer_as_token_source(tokenizer)
    );
    if (parser == NULL) {
        apfl_tokenizer_destroy(tokenizer);
        apfl_raise_alloc_error(ctx);
    }

    struct instruction_list *ilist = setup_function_for_load(ctx, filename);
    if (ilist == NULL) {
        apfl_parser_destroy(parser);
        apfl_tokenizer_destroy(tokenizer);
        apfl_raise_alloc_error(ctx);
    }

    for (;;) {
        switch (apfl_parser_next(parser)) {
        case APFL_PARSE_OK: {
            struct apfl_error err;
            if (!apfl_compile(
                &ctx->gc,
                apfl_parser_get_expr(parser),
                &err,
                ilist
            )) {
                apfl_drop(ctx, -1);
                apfl_parser_destroy(parser);
                apfl_tokenizer_destroy(tokenizer);
                apfl_raise_error_object(ctx, err);
            }

            break;
        }
        case APFL_PARSE_ERROR:
            apfl_drop(ctx, -1);
            apfl_parser_destroy(parser);
            apfl_tokenizer_destroy(tokenizer);
            apfl_raise_error_object(ctx, apfl_parser_get_error(parser));
            break;
        case APFL_PARSE_EOF:
            apfl_parser_destroy(parser);
            apfl_tokenizer_destroy(tokenizer);
            return;
        }
    }
}