Complex expression parser (uses scratchpad.js)

complex-expression.js

!function(){

var orderOfOps = ['+', '-', '*', '/'];
var rules = {
    '+' : 'add',
    '-' : 'subtract',
    '*' : 'multiply',
    '/' : 'divide'
};

function trim( str ){
    return str.replace(/(?:(?:^|\n)\s+|\s+(?:$|\n))/g,'').replace(/\s+/g,' ');
}

var getSubs = function( expr ){
    var start = 0;
    var level = 0;
    var parts = [];
    var count = 0;
    var ch;

    if (!expr) {
        return {
            parts: parts,
            expr: expr
        };
    }

    for ( var i = 0, l = expr.length; i < l; i++ ){

        ch = expr[ i ];
        if ( ch === '(' ){
            level++;
            if ( level === 1 ){
                start = i;
            }
        } else if ( ch === ')' ){
            level--;
            if ( level === 0 ){
                count = parts.push( expr.substring( start + 1, i ) ) - 1;
                expr = expr.slice( 0, start ) + '@' + count + '@' + expr.slice( i + 1 );
                i -= l - expr.length;
                l = expr.length;
            }
        }
    }

    return {
        parts: parts,
        expr: expr
    };
};

var parse = function( expr ){
    
    var idx, op, fn;
    var left, right;
    var subs;

    expr = trim( expr );

    if (!expr){
        return '0';
    }

    subs = getSubs( expr );

    if ( subs.parts.length ){
        return parse(subs.expr).replace(/@([0-9]+)@/g, function( str, n ){
            n = n|0;
            return parse( subs.parts[ n ] );
        });
    }

    for ( var ii = 0, l = orderOfOps.length; ii < l; ii++ ){

        op = orderOfOps[ ii ];
        fn = rules[ op ];

        idx = expr.indexOf( op );

        if ( idx > -1 ){
            left = expr.substr(0, idx);
            right = expr.substr(idx + 1);
            return 'scratch.Complex().fromRect(0,0).add(' + parse(left) + ').' + fn + '(' + parse(right) + ')';
        }
    }

    return expr;
};

PhaseMatch.Complex.expression = function( expr ){
    return PhaseMatch.Scratchpad(new Function('scratch, scope', 'with(scope) return ' + parse( expr ) + '.clone()'));
};

}();