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From: jcp@arizona.edu (John Peterson)
Newsgroups: comp.lang.lisp
Subject: The BEST way to sum a list
Message-ID: <7559@megaron.arizona.edu>
Date: 27 Oct 88 04:17:31 GMT
Organization: U of Arizona CS Dept, Tucson
Lines: 22

The discussion comparing different ways to sum a list has missed an
important point.  Although the solution
  (apply '+ list)
is very elegent, it ignores a basic limitation of Common Lisp: 
call-arguments-limit.  This will not work (nor will eval) if the
list is longer than this value.  CLtL only states this limit must be at
least 50, not much of a list.  To be safe (or at least postable), either the
iterative solution or reduce should be used.  Also, note that this
brings up the issue of whether &rest should provide a freshly consed
list or not.  If it is, &rest would incur the additional overhead of a
list copy.  This issue is not addressed in CLtL.

(There are some very good implementation reasons for this limit.  Using
registers for parameter passing yields dramatic speedup, but only a
finite number of registers or psuedo registers are available.)


    John Peterson
    University of Arizona, Dept of Computer Science
    jcp@megaron.arizona.edu

    Think Granite