Re: [Gcl-devel] Lisp programming style advice

[Paul F. Dietz]

Camm Maguire wrote:
> Greetings!  In the course of addressing some of the ansi issues
> revealed by Paul's tests, I'm finding myself writing ever more
> sophisticated (for me) lisp code for GCL with a still partial
> understanding of the language. I'd like to take a moment to solicit
> the opinions of the list on the with-package-iterator macro I
> committed recently.

(1) Don't write (if <form1> <form2>); write (when <form1> <form2>).
  This is easier to understand when <form2> is very large.
  Similarly, prefer (unless <form1> <form2>) to (if (not <form1>) <form2>).
  The reader should not be forced to scan down the page to search
  for the optional 'else' clause.


(2) Instead of

(progn
   (setq ,q (cdr ,q))
   (if (null ,q)
     ... ))

write

(if (null (setq ,q (cdr ,q)))
   ...)

This reduces the indentation overload.


(3) You probably don't want a big body in a macrolet -- that can lead
  to lots of code expansion.  Instead, use a flet.


(4) Instead of (setq ,i (1+ ,i)), use (incf ,i).


And a bug:

(5) You are assigning a list to ,x at one point, but you declared ,x
  to be a fixnum.  Use multiple-value-setq instead.

(setq ,x (multiple-value-list
          (si::package-size (car ,q))))
(setq ,y (first ,x))
(setq ,x (second ,x))
==>
(multiple-value-setq (,y ,x) (si::package-size (car ,q)))

(You don't want multiple-value-list to be consing up that short
temporary list anyway.)

        Paul