pasaran/01.parser.html

## 01.parser.html
<!doctype html>
<html>
<head>
    <meta charset="utf-8">
    <title>parser.01</title>
    <script src="01.parser.js"></script>
</head>
<body>

<script>
var ast = parse('2 + 3 * (5 - 6)');
console.log( JSON.stringify(ast, null, 4) );
</script>

</body>
</html>


## 01.parser.js
var TOKEN_ADD = /^[+-]/;
var TOKEN_MUL = /^[*/%]/;
var TOKEN_NUMBER = /^[0-9]+(\.[0-9]+)?/;

function parse(s) {
    var p = 0;
    var cur = s;

    var ast = parse(r_expr);
    if (cur) {
        error('End of string expected');
    }

    return ast;

//  ---------------------------------------------------------------------------------------------------------------  //

    function parse(rule) {
        var start = p;
        var ast = rule();

        //  ast._start = start;
        //  ast._end = p;

        return ast;
    }

    function test(token) {
        var r = token.exec(cur);

        return r && r[0];
    }

    function match(token) {
        var result = test(token);

        if (!result) {
            expected(token);
        }

        move(result.length);
        skip();

        return result;
    }

    function eat(s) {
        var l = s.length;
        if ( la(l) !== s ) {
            expected(s);
        }
        move(l);
        skip();

        return s;
    }

    function skip() {
        var r = /^\s+/.exec(cur);
        if (r) {
            move(r[0].length);
        }
    }

    function move(l) {
        l || (l = 1);
        p += l;
        cur = cur.substr(l);
    }

    function la(n) {
        return cur.substr(0, n || 1);
    }

    function expected(id) {
        error('Token ' + id + 'expected');
    }

    function error(msg) {
        throw Error(msg + ' at ' + p + ' : ' + cur);
    }

//  ---------------------------------------------------------------------------------------------------------------  //

    function r_expr() {
        return parse(r_add);
    }

    function r_add() {
        var left = parse(r_mul);

        if (( op = test(TOKEN_ADD) )) {
            match(TOKEN_ADD);

            return {
                _id: 'add',

                op: op,
                left: left,
                right: parse(r_add)
            };
        }

        return left;
    }

    function r_mul() {
        var left = parse(r_primary);

        if (( op = test(TOKEN_MUL) )) {
            match(TOKEN_MUL);

            return {
                _id: 'mul',

                op: op,
                left: left,
                right: parse(r_mul)
            };
        }

        return left;

    }

    function r_primary() {
        if ( la() === '(' ) {
            eat('(');
            var ast = parse(r_expr);
            eat(')');

            return ast;
        }

        return {
            _id: 'number',

            value: +match(TOKEN_NUMBER)
        };
    }

//  ---------------------------------------------------------------------------------------------------------------  //

}
	<!doctype html>
	<html>
	<head>
	<meta charset="utf-8">
	<title>parser.01</title>
	<script src="01.parser.js"></script>
	</head>
	<body>

	<script>
	var ast = parse('2 + 3 * (5 - 6)');
	console.log( JSON.stringify(ast, null, 4) );
	</script>

	</body>
	</html>
	var TOKEN_ADD = /^[+-]/;
	var TOKEN_MUL = /^[*/%]/;
	var TOKEN_NUMBER = /^[0-9]+(\.[0-9]+)?/;

	function parse(s) {
	var p = 0;
	var cur = s;

	var ast = parse(r_expr);
	if (cur) {
	error('End of string expected');
	}

	return ast;

	// --------------------------------------------------------------------------------------------------------------- //

	function parse(rule) {
	var start = p;
	var ast = rule();

	// ast._start = start;
	// ast._end = p;

	return ast;
	}

	function test(token) {
	var r = token.exec(cur);

	return r && r[0];
	}

	function match(token) {
	var result = test(token);

	if (!result) {
	expected(token);
	}

	move(result.length);
	skip();

	return result;
	}

	function eat(s) {
	var l = s.length;
	if ( la(l) !== s ) {
	expected(s);
	}
	move(l);
	skip();

	return s;
	}

	function skip() {
	var r = /^\s+/.exec(cur);
	if (r) {
	move(r[0].length);
	}
	}

	function move(l) {
	l \|\| (l = 1);
	p += l;
	cur = cur.substr(l);
	}

	function la(n) {
	return cur.substr(0, n \|\| 1);
	}

	function expected(id) {
	error('Token ' + id + 'expected');
	}

	function error(msg) {
	throw Error(msg + ' at ' + p + ' : ' + cur);
	}

	// --------------------------------------------------------------------------------------------------------------- //

	function r_expr() {
	return parse(r_add);
	}

	function r_add() {
	var left = parse(r_mul);

	if (( op = test(TOKEN_ADD) )) {
	match(TOKEN_ADD);

	return {
	_id: 'add',

	op: op,
	left: left,
	right: parse(r_add)
	};
	}

	return left;
	}

	function r_mul() {
	var left = parse(r_primary);

	if (( op = test(TOKEN_MUL) )) {
	match(TOKEN_MUL);

	return {
	_id: 'mul',

	op: op,
	left: left,
	right: parse(r_mul)
	};
	}

	return left;

	}

	function r_primary() {
	if ( la() === '(' ) {
	eat('(');
	var ast = parse(r_expr);
	eat(')');

	return ast;
	}

	return {
	_id: 'number',

	value: +match(TOKEN_NUMBER)
	};
	}

	// --------------------------------------------------------------------------------------------------------------- //

	}