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Re: suggestion: a shorter convenience form



Per Bothner skrev:
A problem with define-syntax+syntax-case is that you
get very verbose syntax definitions, with lots of
standard boiler-plate.  This makes syntax definitions
needlessly hard to read and (less important) more tedious to
write.  This has tempted some of my Kawa users to use the "legacy"
non-hygienic define-macro form, even though I discourage it.
Even plain R5RS define-syntax+syntax-rules is
ridiculously verbose.

One idea I had has this little conveniece macro:

(define-syntax define-syntax-case
   (syntax-rules ()
     ((define-syntax-case name literals . parts)
      (define-syntax name
        (lambda form
         (syntax-case form literals . parts))))))

Typical use - especially nice if #` is availiable:

(define-syntax-case NAME ()
  ((_ PVAR ...)
  #`(... PVAR ...))

Of course people can define this themselves, but
it is nicer if it is standard, because then people
get used to reading it.

I assume the standard boiler plate you are thinking
of is

  (define-syntax foo
    (lambda (stx)
       (syntax-case stx ()
          <clauses>)))
?



In analogy with

     (define (foo x)
  == (define foo (lambda (stx) ...))

a common extension to define-syntax is

     (define-syntax (foo stx)
  == (define-syntax foo (lambda (stx) ...))

The "standard boiler plate" then becomes

 (define-syntax (foo stx)
    (syntax-case stx ()
       <clauses>))

This is almost as short as your convenience macro and at
the same time still makes it possible to refer to the original
input syntax-object of the transformer. Refering to the
original piece of syntax is often neccessary in order to give
error messages in terms of user written syntax.



I agree with you that the common case should be convenient
to write, in this case I'm not sure I think it is worth
introducing an extra binding form in order to save relatively
few key strokes.


--
Jens Axel Søgaard