From ...
From: Erik Naggum <erik@naggum.no>
Subject: Re: Mapping by N elements
Date: 1999/04/07
Message-ID: <3132455299515355@naggum.no>#1/1
X-Deja-AN: 463537495
References: <MPG.1173980e8bb1f8e9989681@news.mindspring.com>
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Organization: Naggum Software; +47 8800 8879; http://www.naggum.no
Newsgroups: comp.lang.lisp

* samir@mindspring.com (Samir Barjoud)
| Is there any function or macro defined by Common Lisp that does the
| following?
:
| Here is its fictional documentation:
| 
| (map-by VARLIST LIST &rest BODY)
| 
| A macro returning a list created by binding successive N elements of LIST 
| to the symbols in VARLIST (where N is the length of VARLIST) and 
| executing BODY each time around. The return value of BODY is used as each 
| element of the return list.

  the much undeservedly maligned extended LOOP macro does this for me
  whenever I need the above, which is only when processing property lists:

(loop
  for (key value) on <plist> by #'cddr
  collect (<whatever> key value))

  I don't see a need for a generalization of his idiom.

#:Erik