function lambda(str) {
  var idx = str.indexOf(":");
  var args = str.substring(0,idx).split(",");
  var code = str.substring(idx+1);
  return function () {
    for(var i=0; i< arguments.length; i++) {
      eval("var " + args[i] + " = " + arguments[i]);
    }
    return eval(code);
  };
}


// basic usage
var multiplier = lambda("x: x*2");
alert(multiplier(10));

// execute the function when it returns.
var done = lambda("x,y: Math.pow(x,y)")(12,2);
alert(done);

// adding context, using this and call()
var withThis = lambda(": this+2");
alert(withThis.call(10));

// An empty function returns undefined
var return_undefined = lambda("");
alert(return_undefined());

// Creating a null function
var return_null = lambda(": null");
alert(return_null());