Tamas Papp tkpapp@gmail.com writes:
On Mon, 04 Jul 2011 11:39:39 +0200, Hans Hübner wrote:
On Mon, Jul 4, 2011 at 11:31 AM, Tamas Papp tkpapp@gmail.com wrote:
Why do some CL library functions have :key arguments?
[...]
but it is a bit cumbersome. I can make my code simpler by relying on calls like
(quantiles (map 'vector key vector) quantiles)
This not only conses "a bit more", it also duplicates traversal efforts
- The original list must be traversed, and the consed-up list of key
values as well. I think it is prudent that the CL library functions offer ways to reduce consing for cases where "a bit" is too much (and "a bit" can become a lot if a program operates on long lists).
I understand this. My main question is: why not do this with compiler macros? Is there any reason for this, other than historical?
Because it's not easy to do with compiler macros.
Note that I am not complaining about the standard, I just want to learn the reason for this design choice so that I can take it into account when writing my own libraries.
I find (foo sequence :key #'key) much nicer than (foo (map 'sequence #'key sequence))