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Comment by kryptiskt | Hacker News Reader

R6RS has syntax-case macros which is superior to Common Lisp macros in every respect, they're both hygienic and can be used to implement a sloppy macro system if one so wishes.

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`syntax-rules` is very good and you can do a whole lot with them. However, you are limited to template -> pattern transformations, and there are plenty of macros that you cannot write this way. (E.g. anything requiring a predicate on the source syntax that you can't express in the template language, etc.) For that, you need the full power of procedural macros.

Racket improves on Scheme: its macros are fully hygienic whilst not being limited to template -> pattern transforms. See https://docs.racket-lang.org/guide/macro-transformers.html

EDIT: syntax-case -> syntax-rules; R6RS specifies the latter—I believe the former is a Racket construct equivalent in power to `syntax-rules`.

I think the parent meant that R6RS has `syntax-rules`, which has enough power to implement CL `defmacro` as well as `syntax-case`.

My mistake: R6RS has `syntax-rules`, not `syntax-case` as far as I can tell. However, `syntax-rules` and `syntax-case` are equivalent in power. [1]

It does not have the same power as `defmacro`: you cannot define general procedural macros with `syntax-rules`, as you are limited to the pattern-matching language to compute over and construct syntax objects.

[1]: https://docs.racket-lang.org/reference/stx-patterns.html#%28...

I think you got your wires crossed. R5 and R7 only have `syntax-rules` macros. R6 has both (`syntax-rule` can be trivially defined as a `syntax-case` macro).

R6 having `syntax-case` macros is one of the more controversial things about it; a surprising number of implementers don't care for them.

I found the relevant documentation and you are absolutely correct and I was mistaken. Thank you for setting me straight.

https://www.scheme.com/tspl4/syntax.html#./syntax:h3

I think we're talking past each other. I mean something like:

  (macroexpand '(when-let (foo (frob bar))
      (jib foo)))
  ;; (let ((foo (frob bar)))
  ;;   (when foo
  ;;     (jib foo)))

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