#include "syntax.h"

#include "eval.h"
#include "object.h"

#include <assert.h>

struct Object *syntax_begin(
    struct Object *args,
    struct Object *const environment
) {
    assert(OBJECT_IS_LIST_HEAD(args));
    struct Object *result = NULL;
    while (!OBJECT_IS_NULL(args)) {
        assert(Object_is_pair(args));
        result = eval(args->pair.car, environment);
        args = args->pair.cdr;
    }
    return result;
}

struct Object *syntax_define(
    struct Object *const args,
    struct Object *const environment
) {
    assert(Object_is_pair(args));
    struct Object *const name = args->pair.car;
    assert(Object_is_symbol(name));
    assert(Object_is_pair(args->pair.cdr));
    struct Object *const value_expr = args->pair.cdr->pair.car;
    assert(OBJECT_IS_NULL(args->pair.cdr->pair.cdr));

    assert(Object_is_pair(environment));
    assert(OBJECT_IS_NULL(environment->pair.cdr));
    assert(OBJECT_IS_LIST_HEAD(environment->pair.car));
    environment->pair.car = Object_new_pair(
        Object_new_pair(name, eval(value_expr, environment)),
        environment->pair.car
    );

    return NULL;
}

struct Object *syntax_if(
    struct Object *const args,
    struct Object *const environment
) {
    assert(Object_is_pair(args));
    struct Object *const cond = args->pair.car;
    struct Object *const then_else_list = args->pair.cdr;
    assert(then_else_list);
    assert(Object_is_pair(then_else_list));
    struct Object *const then_branch = then_else_list->pair.car;
    struct Object *const else_list = then_else_list->pair.cdr;
    assert(else_list);
    assert(Object_is_pair(else_list));
    struct Object *const else_branch = else_list->pair.car;
    assert(OBJECT_IS_NULL(else_list->pair.cdr));

    if (Object_is_false(cond)) {
        return eval(else_branch, environment);
    } else {
        return eval(then_branch, environment);
    }
}

struct Object *syntax_quote(
    struct Object *const args,
    struct Object *const environment
) {
    (void)environment; // unused

    assert(Object_is_pair(args));
    assert(OBJECT_IS_NULL(args->pair.cdr));
    return args->pair.car;
}