Re: [PATCH] psyntax: custom ellipses using 'with-ellipsis' or R7RS syntax-rules

[ludo@gnu.org (Ludovic Courtès)]

Hi, Mark,

Mark H Weaver <mhw@netris.org> skribis:

> In the end, here's how this works: 'with-ellipsis' binds a special
> identifier named #{ $sc-ellipsis }# using a new 'ellipsis' binding type.
> The new ellipsis identifier is stored within the binding.  In order to
> determine whether an identifier X is an ellipsis, the binding for
> #{ $sc-ellipsis }# is looked up in the lexical environment of X.  If the
> binding is found and has binding-type 'ellipsis', then X is compared to
> the identifier stored in the binding using 'bound-id=?'.  Otherwise, X
> is compared to '...' using 'free-id=?' as was done before.

This looks nice!  Thanks for providing the detailed reasoning, that’s
insightful.

Does something like this work:

  (define-syntax define-inline
    (with-ellipsis ---
      (syntax-rules ()
        ((_ (name parms ---) exp ---)
         (define-syntax name
            (syntax-rules ()
              ((_ args (--- ---))
               ((lambda (parms ---) exp ---)
                args (--- ---)))))))))

Looks good to me for 2.0.

Could you wrap lines to 80 columns in psyntax.scm?

> +@subsubsection Specifying a custom ellipsis identifier

Should be “Specifying a Custom Ellipsis Identifier”.

> +@subsubsection Custom ellipsis identifiers for syntax-case macros

Likewise.

> +      (define-syntax define-quotation-macros
> +        (lambda (x)
> +          (syntax-case x ()
> +            ((_ (macro-name head-symbol) ...)
> +             #'(begin (define-syntax macro-name
> +                        (lambda (x)
> +                          (with-ellipsis …
> +                            (syntax-case x ()
> +                              ((_ x …)
> +                               #'(quote (head-symbol x …)))))))
> +                      ...)))))

Pretty cool.  :-)

Thanks,
Ludo’.