Re: Bug report

Hello,

Taylor R Campbell a écrit :
> This is the case in the example shown.  The transformation is
> unambiguous, but it could be construed to violate the sentence in the
> R5RS, Section 4.3.2 `Pattern language', p. 15, that reads: `Pattern
> variables that occur in subpatterns followed by one or more instances
> of the identifier ``...'' are allowed only in subtemplates that are
> followed by as many instances of ``...'.'  In the pattern, b is
> followed by one ellipsis, but in the template, it is followed by two.
> 

Thanks for pointing to the relevant part of the report.

However when we try this:

(define-syntax bar
   (syntax-rules ()
     ((bar aa (b ...))
      '((aa b) ...))))

(bar "test" (1 2 3 4))
;; (("test" 1) ("test" 2) ("test" 3) ("test" 4))

You see there that "test" is repeated. Ok, this is because 'aa' is a template 
variable with no ellipsis.

The following one gives an error depending on your implementation:

(define-syntax baz
   (syntax-rules ()
     ((baz (a ...) (b ...))
      '(((a ...) b) ...))))

(baz ("test") (1 2 3 4))

I mean if there is more ellipsis in the template than in the pattern, some macro 
expanders repeat the whole template variable as it is.

> You were probably thinking of transforming (foo (a ...) (b ...)) into
> (list (list a b) ...), which of course makes no sense for (foo (1 2 3)
> (4 5)).  Some Scheme systems support this nevertheless -- Scheme48 and
> MIT Scheme just truncate the longer list in the bogus case.
> 

I suppose this one is vague because (a ...) could match the empty list ?

> Another cute trick is transforming (foo (a ...) ...) into (foo a ...
> ...), which Scheme48 supports, but which some other Scheme systems
> such as MIT Scheme don't.  Whether this is kosher in the R5RS is a
> little fuzzier; it depends on whether one is willing to weasel about
> with the term `followed by'.
> 

Exactly, we need to clear confusion about that.

Best regards,
--

begin:vcard
fn:Emmanuel Medernach
n:Medernach;Emmanuel
org:IN2P3/CNRS ;63177 AUBIERE CEDEX
adr:;;;Clermont-Ferrand;;63000;France
email;internet:[email protected]
title:Laboratoire de Physique Corpusculaire
x-mozilla-html:FALSE
version:2.1
end:vcard