`(scheme aux)` is a clever idea. I don't think define-syntax is enough to guarantee keyword hygiene, though.

If you `(define-syntax <>)`, it's still possible to write `(let ((<> 1)) <>)` without errors. That makes it possible for something inside the `let` scope to unhygenically insert a `<>` into a macro that uses `cut` or `chain` internally. An identifier macro would prevent this.

On 8/12/20 9:53 PM, John Cowan wrote:

Identifier macros aren't necessary.  For example, to make <- work as shared auxiliary syntax, just bind it like this:

(define-syntax <-

  (syntax-rules ()

    ((** head . tail)

     (syntax-error "invalid auxiliary syntax" head . tail))))

Now (<- 1 2 3) will signal an expansion-time error, and (+ 0 <-) will too because an ordinary macro can't be used in operand position.

Then you provide the magic (scheme aux) library, which binds every possible keyword using the above syntax-rules definition.  Of course you always refer to it like (import (only (scheme aux) **)).  Easy-peasy.

John Cowan          http://vrici.lojban.org/~cowan        xxxxxx@ccil.org
One Word to write them all / One Access to find them,
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                --Mike Champion