iterate is a lispy and extensible replacement for the LOOP macro. It is also a utility library.

It was written by Jonathan Amsterdam at MIT and recently ported to Common Lisp.

The canonical site for information about iterate is at

Some examples:

(iterate (for (key . item) in alist)
  (collect key into keys)
  (collect item into items)
  (finally (return (values keys items))))
collects keys and items of an alist into two values

It also supports generators:

(iterate (generate i from 0 to 6)
  (for (key . value) in '((a . 2) (zero . 10) (one . 20) (d . 5)))
  (when (>= value 10)
    (collect (cons key (next i)))))

   => ((ZERO . 0) (ONE . 1))

and allows easy finding of extrema:

(iterate (for elt in list-of-lists)
  (finding elt maximizing (length elt)))
finds the longest list in a list of lists and generates pretty fast code, too. (-:

language extension