KennethParnell.com

Yes, Ruby can do this

But seeing as I am a fan of Object Oriented programming. (Ruby in particular)

I would change:

    function map(fn, a)
    {
         for (i = 0; i < a.length; i++)
         {
             a[i] = fn(a[i]);
         }
     }

to:

    Array.prototype.map = function( fn ){
        result = new Array();
        for ( var i = 0; i < this.length; i++ ){
            result[i] = fn(this[i]);
        }
        return result;
    }

now you can do:

    var a = [1,2,3];
    a.map( function(num){return num*2;} );
    a.map( alert );