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Re: Ellipsis in the _pattern_

This page is part of the web mail archives of SRFI 46 from before July 7th, 2015. The new archives for SRFI 46 contain all messages, not just those from before July 7th, 2015.

On Fri, 10 Oct 2003, Taylor Campbell wrote:

>Since with this SRFI it becomes possible to put literal ellipsis in the
>_template_, it seems like it would be useful to also be able to match
>literal ellipsis in the _pattern_, while still being able to use
>to match multiple inputs.  However, I cannot think of a nice and concise
>way to do this: enabling literal ellipsis to be present in the literal
>identifier list would prohibit the macro from using ellipsis to match
>multiple inputs.  Any comments on this idea, and how to go about it?

It would certainly be possible to do it using an additional identifier;
An "obvious" choice, which is a legal identifier according to R5RS,
would be :::  .  Other "obvious" choices which are legal identifiers
include <...> or /.../ .  The first of those two is particularly tasty
because it allows a general "nested" syntax; you could use
<<...>>, <<<...>>>, etc, for more layers of nesting.

One thing to remember though, is that an ellipsis matches anything
in the code it's matching against -- including another ellipsis.
So there may actually be no issue here.