lesson-lisp/parser.c

#include "parser.h"

#include "enums.h"
#include "object.h"
#include "tokens.h"

#include <assert.h>
#include <stddef.h>
#include <stdlib.h>

static void expect(enum TokenType token_type);

static struct Object *expr();
static struct Object *parens();
static struct Object *parens_part();

void expect(const enum TokenType token_type)
{
    assert(tokens_expect(token_type));
}

struct Object *parse()
{
    return expr();
}

struct Object *expr()
{
    assert(tokens_top());

    switch (tokens_top()->type) {
    case TOKEN_OPEN: return parens();
    case TOKEN_SYMBOL:
    {
        struct Object *const object = Object_new_symbol(tokens_top()->val);
        tokens_pop();
        return object;
    }
    case TOKEN_NUM:
    {
        struct Object *const object =
            Object_new_number(atoll(tokens_top()->val));
        tokens_pop();
        return object;
    }
    default:
        abort();
        return NULL;
    }
}

struct Object *parens()
{
    expect(STATE_OPEN);
    struct Object *const object = parens_part();
    expect(STATE_CLOSE);
    return object;
}

struct Object *parens_part()
{
    assert(tokens_top());
    if (tokens_top()->type == TOKEN_CLOSE) return NULL;

    struct Object *const a = expr();
    assert(tokens_top());

    struct Object *b = NULL;
    if (tokens_top()->type != TOKEN_CLOSE) {
        b = parens_part();
    }

    struct Object *object = Object_new_pair(a, b);
    return object;
}