[R6RS] syntax-case

[R. Kent Dybvig]

> Frankly I don't see why there needs to be a separate form for identifiers.
> Couldn't this be folded into syntax-case?

Generalized identifier macros can be written using syntax-case in both
Chez Scheme and DrScheme, only (set! keyword expr) is a syntax error
unless the transformer associated with keyword is marked somehow as
willing to accept set! forms, e.g., something like:

  (define-syntax foo
    (set!-aware-transformer
      (lambda (x)
        (syntax-case x (set! :=)
          [id (identifier? #'id) #'bar]
          [(set! _ y) #'(set! bar y)]
          [(_ := y) #'(set! bar y)]))))

This frees the more common macros that don't need to handle set!
expressions from having to deal with the possibility of being handed one.

Kent