At Thu, 07 May 2009 22:33:06 +0200, "Marijn Schouten (hkBst)" wrote:
> I found a difference in running a file with "mzscheme -f <file>" and with
> "plt-r6rs <file>" involving syntax-case. For the first you should comment the
> import. Then the first will error:
>
> cdr: expects argument of type <pair>; given #<syntax:blah>
>
> and the second will produce the expected output:
>
> (a b (+ c -1) d e)
>
> The code is:
>
>
> (import (rnrs)) ;comment this line for mzscheme
>
> (define make-next-coords
> (lambda (x)
> (with-syntax (((name ... pos inc) x))
> (let ((pos (syntax->datum #'pos)))
> (let f ((names #'(name ...))(pos pos))
> (with-syntax (((name rest ...) names))
> (if (zero? pos)
> #'((+ name inc) rest ...)
> #`(name #,@(f (cdr names)(- pos 1))))))))))
>
> (write (syntax->datum (make-next-coords #'(a b c d e 2 -1))))
>
>
> Is this a bug or is there another explanation?
R6RS and PLT Scheme have different rules about syntax-object wrapping.
Specifically,
#'(name ...)
generates a list in R6RS, but it's a wrapped[*] syntax object in PLT
Scheme. In the latter case, `syntax->list' is the simplest way to
convert the syntax object to a list.
One reason for this difference is that the implicit
procedure-application form is lexically scoped in PLT Scheme (and you
can redefine it by binding `#%app'), which means that a lexical context
must be attached to parentheses (roughly speaking).
[*] "Wrapped syntax object" is R6RS terminology. In PLT Scheme
terminology, all "syntax object" always implies a wrapper.
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