clarification for regexp-replace in srfi-115 / chibi.regex

[Duy Nguyen]

This was posted in srfi-115 list, but I hope to catch Alex's attention
by doing it here instead.

'subst' parameter of regexp-replace is described like this

---
subst can be a string, an integer or symbol indicating the contents of
a numbered or named submatch of re, 'pre for the substring to the left
of the match, or 'post for the substring to the right of the match.
---

This makes replacement very limited. I found that chibi.regex accepts
'subst' as a _list_ of those items too. With that we can start doing
something like this regexp

s/\(<first>\)...\(<second>\)/blah \2 - \1/'

The SRFI should probably mention that it is an error if a capture
group is named 'pre or 'post because it's ambiguous. Each Scheme
implementation can decide whatever they want to do in that case.

Also, 'subst' can be a procedure in chibi.regex and that makes
replacement much more flexible.


Is it reasonable to amend the SRFI like above? As far as I know, all
srfi-115 implementations out there are based on chibi.regex, which
already supports that. The only exception is Gauche, which translates
SRE to its own AST syntax, and I made sure that it supports the same.

If the SRFI is set in stone, I think we could make a new one and let
it be voted to replace srfi-115 in r7rs-large.
--
Duy

[Alex Shinn]

Thanks for the ping, I'll follow up on the SRFI list.

--

Alex

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