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

[Ludovic Courtès]

Hi,

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.

Ludo’.