quack/quack

<?php
/**
 * Quack Compiler and toolkit
 * Copyright (C) 2015-2017 Quack and CONTRIBUTORS
 *
 * This file is part of Quack.
 *
 * Quack is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Quack is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Quack.  If not, see <http://www.gnu.org/licenses/>.
 */
namespace QuackCompiler\Lexer;

abstract class Lexer
{
    const EOF      = -1;
    const EOF_TYPE = 0;

    public $input;
    public $position = 0;
    public $peek;

    protected $words = [];

    public $keywords = [];

    public function __construct($input)
    {
        $this->size = strlen($input);

        if ($this->size === 0) {
            exit;
        }

        $this->input = $input;
        $this->peek  = $input[0];

        // Reserve keywords
        $this->reserve(new Word(Tag::T_LET, 'let'));
        $this->reserve(new Word(Tag::T_IF, 'if'));
        $this->reserve(new Word(Tag::T_WHILE, 'while'));
        $this->reserve(new Word(Tag::T_DO, 'do'));
        $this->reserve(new Word(Tag::T_FOREACH, 'foreach'));
        $this->reserve(new Word(Tag::T_IN, 'in'));
        $this->reserve(new Word(Tag::T_MOD, 'mod'));
        $this->reserve(new Word(Tag::T_WHERE, 'where'));
        $this->reserve(new Word(Tag::T_CONTINUE, 'continue'));
        $this->reserve(new Word(Tag::T_BREAK, 'break'));
        $this->reserve(new Word(Tag::T_AND, 'and'));
        $this->reserve(new Word(Tag::T_OR, 'or'));
        $this->reserve(new Word(Tag::T_XOR, 'xor'));
        $this->reserve(new Word(Tag::T_ELIF, 'elif'));
        $this->reserve(new Word(Tag::T_ELSE, 'else'));
        $this->reserve(new Word(Tag::T_NOT, 'not'));
        $this->reserve(new Word(Tag::T_FN, 'fn'));
        $this->reserve(new Word(Tag::T_THEN, 'then'));
        $this->reserve(new Word(Tag::T_BEGIN, 'begin'));
        $this->reserve(new Word(Tag::T_END, 'end'));
        $this->reserve(new Word(Tag::T_BY, 'by'));
        $this->reserve(new Word(Tag::T_UNLESS, 'unless'));
        $this->reserve(new Word(Tag::T_MUT, 'mut'));
        $this->reserve(new Word(Tag::T_TYPE, 'type'));
        $this->reserve(new Word(Tag::T_MATCH, 'match'));
        $this->reserve(new Word(Tag::T_WITH, 'with'));
        $this->reserve(new Word(Tag::T_DATA, 'data'));
    }

    private function reserve(Word $t)
    {
        $this->keywords[$t->getTag()] = $t->lexeme;
        $this->words[$t->lexeme] = $t;
    }

    protected function isEnd()
    {
        return $this->position >= $this->size;
    }

    public function rewind()
    {
        if ($this->size === 0) {
            exit;
        }

        $this->position = 0;
        $this->peek = $this->input[0];
    }

    public function consume($n = 1)
    {
        $this->position += $n;
        $this->peek = $this->isEnd()
            ? self::EOF
            : $this->input[$this->position];
    }

    public function stepback($n = 1)
    {
        $pos = $this->position - $n;
        $this->position = max($pos, 0);
        $this->peek = $this->input[$this->position];
    }

    public function preview($n = 1)
    {
        $next = $this->position + $n;

        return $next >= $this->size
            ? self::EOF
            : $this->input[$next];
    }

    public function previous()
    {
        $previous = $this->position - 1;
        return $previous < 0
            ? null
            : $this->input[$previous];
    }

    public function matches($string)
    {
        $len = strlen($string);

        for ($i = 0; $i < $len; $i++) {
            if ($this->preview($i) !== $string[$i]) {
                return false;
            }
        }

        return true;
    }

    protected function getWord($word)
    {
        return isset($this->words[$word])
            ? $this->words[$word]
            : null;
    }

    public function is($symbol)
    {
        return $this->peek === $symbol;
    }

    abstract public function nextToken();
}