Comments on: List comprehensions in Common Lisp

By: Janon

Wed, 21 Nov 2007 16:19:45 +0000

Example #1 in J

1 line
(I.2= /”1 n){[n=.3 3#:i.*:3

3 lines
cp=. 3 3 #: i. *: 3
ix=. I. 2= /”1 cp
ix { cp

0 2
1 1
2 0

for boxes
<”1 ix { cp
|0 2|1 1|2 0|

By: Moocow Says Moo

Tue, 20 Nov 2007 18:39:47 +0000

Relevant ref to another ready-to-go list comprehensions library, probably the default one a long-time lisper will reach for first (it is mentioned in Mario’s paper, but he dismisses it because it looks complex and possibly slow, which is rather missing the point: Sven’s focus was on versatility - “Collect” is extensible to work with any lisp type, which nice. Very nice. i.e. it’s “almost anything comprehensions”, not just “list comprehensions”:
http://user.it.uu.se/~svenolof/Collect/

By: Tac-Tics

Tue, 20 Nov 2007 15:33:53 +0000

I wrote a list comprehension macro the other day. I don’t use CL, but I was reading up on it, and I thought it would be an interesting exercise. But I gave mine a different form:

(zf (* x y)
(x ‘(1 2 3 4))
(y ‘(1 2 3 4))
if (evenp x)
(oddp y))

I used zf for the name, as list comprehensions are sometimes called Zermelo–Fraenkel expressions, and because zf is really short and stands out. The if marker in the middle breaks the sets from the conditions, avoiding the prefix <- form and makes the whole thing slightly easier on the eyes. (Again, I’m not a Lisper, so I don’t have the Paren-Sight yet ;-)

It’s cool to see someone else doing the same thing.

By: Roger Sen

Tue, 20 Nov 2007 15:32:40 +0000

You’ll find this paper from Guy Lapalme interesting:
http://rali.iro.umontreal.ca/Publications/urls/LapalmeLispComp.pdf