Re: Bug with macros in SCM and Guile

[Aubrey Jaffer <agj@alum.mit.edu>]

If we take the first DEFMACRO out of the begin, then macro expansion
works correctly in both SCM and Guile:

  bash-3.1$ slib guile
  guile> (require 'defmacroexpand)
  guile> (require 'pretty-print)
  guile> (defmacro foo (x)
     (display "expanding-foo-version1\n")
     `(list 'foo-v1 ',x))
  guile> (pretty-print (defmacro:expand* '(begin
  (define (bar1)    (foo in-bar1))
  (define (bar2) #f (foo in-bar2))
  (define (bar3)    (foo in-bar3))
  (write (bar1)) (newline)
  (defmacro foo (x)
     (display "expanding-foo-version2\n")
     `(list 'foo-v2 ',x))
  (write (bar2)) (newline)
  (write (bar3)) (newline)
  )))

Guile prints:

  expanding-foo-version1
  expanding-foo-version1
  expanding-foo-version1

  (begin
    (define (bar1) (list 'foo-v1 'in-bar1))
    (define (bar2) #f (list 'foo-v1 'in-bar2))
    (define (bar3) (list 'foo-v1 'in-bar3))
    (write (bar1))
    (newline)
    (eval-case
      ((load-toplevel)
       (define foo
	 (defmacro:transformer
	   (lambda (x)
	     (display "expanding-foo-version2
  ")
	     `(list 'foo-v2 ',x)))))
      (else (error "defmacro can only be used at the top level")))
    (write (bar2))
    (newline)
    (write (bar3))
    (newline))

SCM prints:

  expanding-foo-version1
  expanding-foo-version1
  expanding-foo-version1

  (begin
    (define (bar1) (list 'foo-v1 'in-bar1))
    (define (bar2) #f (list 'foo-v1 'in-bar2))
    (define (bar3) (list 'foo-v1 'in-bar3))
    (write (bar1))
    (newline)
    (defmacro:simple-defmacro
      foo
      scm:G21
      (let ((scm:G22 scm:G21))
	(let ((x (car scm:G22)))
	  (display "expanding-foo-version2
  ")
	  `(list 'foo-v2 ',x))))
    (write (bar2))
    (newline)
    (write (bar3))
    (newline))

In both cases, the definintions of the bar routines are expanded; so
subsequent DEFMACROs will have no effect on them.

It is disturbing that "expanding-foo-version1" is printed out when
DEFMACRO:EXPAND is expanding the code (both in SCM and Guile).  There
is no call to eval in "defmacex.scm".  How does this happen?


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