Implement 'filter' in Scheme

[Katie Burke]

filter should return a list of the elements of list for which procedure returns true.
http://www.scheme.com/tspl4/objects.html#./objects:s55
This example should return (1 3).

(filter odd? '(1 2 3 4))

Traceback (most recent call last): File "stdin", line 1, col 2 RunTimeError: unbound variable 'filter'