[Sbcl-help] DEFCONSTANT at compile time/load time

[Edi W. <ed...@ag...>]

Hi!

I have a file foo.lisp with the following contents:

  (defun foo (n)
    (1+ n))

  (defconstant +bar+ (foo 10))

If I try to compile it, SBCL (0.7.10 on Linux) complains:

  * (compile-file "foo")
  ; compiling file "/tmp/foo.lisp" (written 01 DEC 2002 07:02:20 PM):
  ; recognizing DEFUN FOO
  ; compiling top level form:
  ; compiling DEFUN FOO:
  ; compiling top level form:

  debugger invoked on condition of type UNDEFINED-FUNCTION:
    The function FOO is undefined.

OK, that's what I expected. The CLHS says about DEFCONSTANT that
"users must ensure that the initial-value can be evaluated at compile
time". OK, let's try it again, foo.lisp now is:

  (eval-when (:compile-toplevel :execute :load-toplevel)
    (defun foo (n)
      (1+ n)))

  (defconstant +bar+ (foo 10))

Which basically works...

  * (compile-file "foo")
  ; compiling file "/tmp/foo.lisp" (written 01 DEC 2002 07:03:55 PM):
  ; recognizing DEFUN FOO
  ; compiling top level form:
  ; compiling DEFUN FOO:
  ; compiling top level form:
  ; compiling top level form:

  ; /tmp/foo.fasl written
  ; compilation finished in 0:00:00

  #P"/tmp/foo.fasl"
  NIL
  NIL
  * (load "foo")
  STYLE-WARNING: redefining FOO in DEFUN

  T

...except for the strange STYLE-WARNING. However, as soon as FOO gets
a little more complicated, like, say, so...

  (eval-when (:compile-toplevel :execute :load-toplevel)
    (defun foo (n c)
      (make-string n :initial-element c)))

  (defconstant +bar+ (foo 10 #\a))

...it won't work:

  * (compile-file "foo")
  ; compiling file "/tmp/foo.lisp" (written 01 DEC 2002 07:04:44 PM):
  ; recognizing DEFUN FOO
  ; compiling top level form:
  ; compiling DEFUN FOO:
  ; compiling top level form:
  ; compiling top level form:

  ; /tmp/foo.fasl written
  ; compilation finished in 0:00:00

  #P"/tmp/foo.fasl"
  NIL
  NIL
  * (load "foo")
  STYLE-WARNING: redefining FOO in DEFUN

  debugger invoked on condition of type SIMPLE-ERROR:
    The constant +BAR+ is being redefined.

Why is that? From my limited understanding of the compilation process
I guess that there's something left over from the compilation
environment which is responsible for the STYLE-WARNING as well as for
the error shown.

Is this correct behaviour? And if so, how am I supposed to deal with
it? Wrap all DEFCONSTANTs into something like

  (unless (boundp '+bar+)
    (defconstant +bar+ ...))

or what?

Thanks for your help,
Edi.

PS: All three examples above were executed in a freshly started
    image. AllegroCL, LispWorks, CMUCL, and CLISP don't show this
    behaviour.