lesson-lisp/src/syntax.c

#include "syntax.h"

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

#include <assert.h>

struct Object *syntax_begin(struct Object *args)
{
    assert(OBJECT_IS_LIST_HEAD(args));
    struct Object *result = NULL;
    while (!OBJECT_IS_NULL(args)) {
        assert(Object_is_pair(args));
        result = eval(args->pair.a);
        args = args->pair.b;
    }
    return result;
}

struct Object *syntax_if(struct Object *const args)
{
    assert(Object_is_pair(args));
    struct Object *const cond = args->pair.a;
    struct Object *const then_else_list = args->pair.b;
    assert(then_else_list);
    assert(Object_is_pair(then_else_list));
    struct Object *const then_branch = then_else_list->pair.a;
    struct Object *const else_list = then_else_list->pair.b;
    assert(else_list);
    assert(Object_is_pair(else_list));
    struct Object *const else_branch = else_list->pair.a;
    assert(OBJECT_IS_NULL(else_list->pair.b));

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

struct Object *syntax_quote(struct Object *const args)
{
    assert(Object_is_pair(args));
    assert(OBJECT_IS_NULL(args->pair.b));
    return args->pair.a;
}