Re: More LOOP fan mail.

[George J. Carrette <GJC at MIT-MC>]

A macsyma system programmer used loop in an includef
file:

(LOOP FOR X IN PRELUDE-FILES
      COLLECT X
      COLLECT (GET X 'VERSION))

However, we made him remove it to save us the slowdown of the
loading of loop.
He grudingly replaced it with this:
	      
(DO ((X PRELUDE-FILES (CDR X))
     (RESULT NIL))
    ((NULL X) (NREVERSE RESULT))
    (PUSH (CAR X) RESULT)
    (PUSH (GET (CAR X) 'VERSION) RESULT))

Ok, uglier than the loop, maybe. But there is a nice mapping way
to do it:

(MAPCAN #'(LAMBDA (X) `(,X ,(GET X 'VERSION))) PRELUDE-FILES)

Here are the results from compiling these three examples:
(in GJC;LOOPT >)

Example | code size (pdp10).
-------------------------------
LOOP     29.
DO       23.
MAP      11.  including SUBR generated from the LAMBDA.
MAP      27.  with MAPEX T to give open compilation.

The LOOP macro produces almost three times as much
machine code as the map in this example.

Observations?
Using LOOP avoided using back-quote.
GLS: Doesn't an optimizing compiler have a tougher time
with a PROG construct and GO-TO's than with a regularized
mapping construct?

Maybe we need a shorter name for lambda, so people won't
be afraid to type it?

How do the proposed NIL mapping extensions compare with
LOOP?

-gjc