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bug#36772: feature request: checked variant of "substitute*"

From: Ludovic Courtès
Subject: bug#36772: feature request: checked variant of "substitute*"
Date: Thu, 25 Jul 2019 19:40:48 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.2 (gnu/linux)


Ricardo Wurmus <address@hidden> skribis:

>> I think it would be great to have the following variant of substitute*:
>> (substitute*-once filename (pattern vars) body)
>> which acts like the usual substitute-*, except it also asserts that the
>> substitution applies to exactly one line in the file, causing a build
>> failure otherwise.
> I agree that the effect of substitute* should be checked.  I think
> substitute* should fail when one of its clauses failed to match
> anything.
> Each clause could also accept an optional argument to make them only
> match one location.  We wouldn’t have to duplicate the macro for that
> and it’s a simple extension to failing on zero matches.
> What do you think?

That’d be a useful extension.


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