interpolate.js

// non-latent version
function Tokenizer(cb) {
	var rules = [];
	var buf = '';
	
	function test(buf) {
		for (var kk in rules) {
			var rule = rules[kk];
			if (rule[0].test(buf)) return rule;
		}
	}
	
	var prev_rule = null;
	return {
		addRule : function (regex,token) {
			rules.push([regex,token]);
		},
		write : function (str) {	
			for (var k in str) {
				var ch = str[k];
				var rule = prev_rule;
				if (rule) {
					if (rule[0].test(buf+ch)) {
						buf += ch;	
					} else {	
						cb(buf,{type:prev_rule[1]});
						buf = ch;
						prev_rule = test(buf);
					} 	
				} else {
					buf += ch
					prev_rule = test(buf);	
				}
			}
		},
		end : function () {
			var rule = test(buf);
			if (rule) cb(buf,{type:rule[1]});
		}
	}	
}

function tk(cb) {
	var t = new Tokenizer(cb);
    
    t.addRule(/^\/\*([^*]|\*(?!\/))*\*\/$/, 'area comment');
    t.addRule(/^\/\*([^*]|\*(?!\/))*\*?$/, 'area comment continue');
    
    t.addRule(/^\/\/[^\n]*$/, 'line comment');
    t.addRule(/^"([^"\n]|\\")*"?$/, 'quote');
    t.addRule(/^'(\\?[^'\n]|\\')'?$/, 'char');
    t.addRule(/^'[^']*$/, 'char continue');
    
    t.addRule(/^#(\S*)$/, 'directive');
    
    t.addRule(/^\($/, 'open paren');
    t.addRule(/^\)$/, 'close paren');
    t.addRule(/^\[$/, 'open square');
    t.addRule(/^\]$/, 'close square');
    t.addRule(/^{$/, 'open curly');
    t.addRule(/^}$/, 'close curly');
    
    t.addRule(
        /^([-<>~!%^&*\/+=?|.,:;]|->|<<|>>|\*\*|\|\||&&|--|\+\+|[-+*|&%\/=]=)$/,
        'operator'
    );
    
    t.addRule(/^([_A-Za-z]\w*)$/, 'identifier');
    
    t.addRule(/^[-+]?[0-9]*\.?[0-9]+([eE][-+]?[0-9]+)?$/, 'number');
    t.addRule(/^(\s+)$/, 'whitespace');
    
    t.addRule(/^\\\n?$/, 'line continue');
    
    return t;
}

function wrap(source) {
	var out = '';
	var x = tk(function(src,token){
		console.log(src,token)
		if (token.type == 'identifier') {
			out += "this." + src;
		} else {
			out += src;	
		}
		});
	x.write(source);
	x.end();
	return out;	
}

function make_fn(str) {
	return eval("function test() { return " + str + " }; test");
}

var fn = make_fn(wrap("xyz*(x+x)"));
console.log(fn.call({x:4,xyz:2}));