apfl/src/context.c

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

#include "apfl.h"
#include "alloc.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, bool with_error_on_stack, enum apfl_result result)
{
    (void)ctx;
    (void)result;
    (void)with_error_on_stack;
    fprintf(stderr, "panic!\n");
    // TODO: more details
    abort();
}

enum apfl_result
apfl_call_protected(apfl_ctx ctx, apfl_stackidx func, apfl_stackidx args, bool *with_error_on_stack)
{
    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) {
        apfl_call(ctx, func, args);
    } else {
        result = (enum apfl_result)(rv - RESULT_OFF_FOR_LONGJMP);
        assert(result != APFL_RESULT_OK);

        struct apfl_value err;
        if ((*with_error_on_stack = handler.with_error_on_stack)) {
            if (!apfl_stack_pop(ctx, &err, -1)) {
                *with_error_on_stack = false;
                // TODO: Indicate error during error handling
            }
        }

        apfl_gc_tmproots_restore(&ctx->gc, tmproots);
        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) {
            if (!apfl_stack_push(ctx, err)) {
                *with_error_on_stack = false;
                // TODO: Indicate error during error handling
            }
        }
    }

    ctx->error_handler = prev_handler;

    return result;
}

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

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

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

    panic(ctx, with_error_on_stack, type);
}

APFL_NORETURN void
apfl_raise_error_with_type(apfl_ctx ctx, apfl_stackidx idx, enum apfl_result type)
{
    bool ok = current_stack_move_to_top(ctx, idx);
    raise_error(ctx, ok, type);
}

APFL_NORETURN void
apfl_raise_const_error(apfl_ctx ctx, enum apfl_result type, const char *message)
{
    raise_error(ctx, try_push_const_string(ctx, message), type);
}

APFL_NORETURN void
apfl_raise_alloc_error(apfl_ctx ctx)
{
    apfl_raise_const_error(ctx, APFL_RESULT_ERR_FATAL, apfl_messages.could_not_alloc_mem);
}

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

APFL_NORETURN void
apfl_raise_error_object(apfl_ctx ctx, struct apfl_error error)
{
    enum apfl_result errtype = APFL_RESULT_ERR;
    if (apfl_error_is_fatal_type(error.type)) {
        errtype = APFL_RESULT_ERR_FATAL;
    }

    const char *const_str = apfl_error_as_const_string(error);
    if (const_str != NULL) {
        apfl_raise_const_error(ctx, errtype, 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_with_type(ctx, -1, errtype);
}

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);
    }
}

static bool
current_stack_move_to_top(apfl_ctx ctx, apfl_stackidx index)
{
    struct stack *stack = current_value_stack(ctx);

    struct apfl_value val;
    if (!stack_get_and_adjust_index(stack, &val, &index)) {
        return false;
    }

    size_t absindex = (size_t)index;

    // If we're here, index is an absolute address and is guaranteed to be < len
    assert(stack->len >= absindex+1);

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

    return true;
}

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++) {
        struct gc_object *object = apfl_value_get_gc_object(stack.items[i]);
        if (object != NULL) {
            visitor(opaque, object);
        }
    }
}

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
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 CSE_FUNCTION:
        visitor(
            opaque,
            GC_OBJECT_FROM(cse.func.instructions, GC_TYPE_INSTRUCTIONS)
        );

        visit_nullable_scope(cse.func.scope, visitor, opaque);
        visit_nullable_scope(cse.func.closure_scope, visitor, opaque);
        break;
    case CSE_CFUNCTION:
        visitor(
            opaque,
            GC_OBJECT_FROM(cse.cfunc.func, GC_TYPE_CFUNC)
        );
        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();
}

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

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;
        }

        // TODO: It's silly that we need to copy the name into a new gc string.
        //       It should be possible for the scope to also have a const string
        //       as a name.
        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;
        }

        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_allocator base_allocator)
{
    apfl_ctx ctx = ALLOC_OBJ(base_allocator, struct apfl_ctx_data);
    if (ctx == NULL) {
        return NULL;
    }

    apfl_gc_init(&ctx->gc, base_allocator, get_roots, ctx);

    ctx->toplevel_stack = apfl_stack_new();
    ctx->call_stack = call_stack_new();

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

    ctx->error_handler = NULL;
    ctx->panic_callback = NULL;
    ctx->panic_callback_data = NULL;

    ctx->iterative_runners = iterative_runners_list_new();

    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;
}

bool
apfl_ctx_register_iterative_runner(apfl_ctx ctx, apfl_iterative_runner runner)
{
    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
    );
}

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_const_error(ctx, APFL_RESULT_ERR, apfl_messages.not_a_list);
    }

    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_RESULT_ERR, 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_RESULT_ERR, 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_RESULT_ERR, 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}));
}

void
apfl_get_member(
    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));
    }

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

    switch (result) {
    case GET_ITEM_OK:
        break;
    case GET_ITEM_KEY_DOESNT_EXIST:
        apfl_raise_const_error(ctx, APFL_RESULT_ERR, apfl_messages.key_doesnt_exist);
        break;
    case GET_ITEM_NOT_A_CONTAINER:
        apfl_raise_const_error(ctx, APFL_RESULT_ERR, apfl_messages.value_is_not_a_container);
        break;
    case GET_ITEM_WRONG_KEY_TYPE:
        apfl_raise_const_error(ctx, APFL_RESULT_ERR, apfl_messages.wrong_key_type);
        break;
    }
}

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_RESULT_ERR, apfl_messages.not_a_list);
    }

    if (index >= list.list->len) {
        apfl_raise_const_error(ctx, APFL_RESULT_ERR, 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]);

    return;
}

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:
        apfl_raise_const_error(ctx, APFL_RESULT_ERR, apfl_messages.wrong_type);
        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;
}

struct apfl_string_view
apfl_get_string(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_LIST:
    case VALUE_DICT:
        apfl_raise_const_error(ctx, APFL_RESULT_ERR, apfl_messages.wrong_type);
        goto error;
    case VALUE_STRING:
        return apfl_string_view_from(*value.string);
    case VALUE_CONST_STRING:
        return value.const_string;
    }

error:
    assert(false);
    return (struct apfl_string_view) {.bytes = NULL, .len = 0};
}

static struct scope *
closure_scope_for_func_inner(apfl_ctx ctx)
{
    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;
    }

    struct call_stack_entry *entry = apfl_call_stack_cur_entry(ctx);
    if (entry == NULL || entry->type != CSE_FUNCTION) {
        return out;
    }

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

    if (entry->func.closure_scope != NULL) {
        if (!apfl_scope_merge_into(out, entry->func.closure_scope)) {
            return NULL;
        }
    }

    if (entry->func.scope != NULL) {
        if (!apfl_scope_merge_into(out, entry->func.scope)) {
            return NULL;
        }
    }

    return out;
}

struct scope *
apfl_closure_scope_for_func(apfl_ctx ctx)
{
    size_t tmproots = apfl_gc_tmproots_begin(&ctx->gc);
    struct scope *out = closure_scope_for_func_inner(ctx);
    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_RESULT_ERR, 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 != 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_RESULT_ERR, 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_RESULT_ERR, apfl_messages.wrong_type);
    }
    return value.userdata;
}