Re: pcase-dolist

[Tassilo Horn]

Stefan Monnier <address@hidden> writes:

>>   (pcase-let ((`(,w ,x ,y ,z) '(1 2 3)))
>>     (message "%s %s %s %s" w x y z))
>
>> prints "1 2 3 nil" although the pattern when used in `pcase' wouldn't
>> match that list but only 4-element lists.  So a pcase pattern has
>> different semantics depending on whether it is used in `pcase' or
>> `pcase-let' or `pcase-dolist' which doesn't feel right.
>
>> I'd prefer if `pcase-let' would signal an error if some pattern doesn't
>> match.
>
> So you'd want the above to signal an error in the case of:
>
>    (pcase-let ((`(,w ,x) '(1 2 3)))
>      (message "%s %s" w x))
>
> ?

Yes, if you want to pick the first two elements of a list with 2 or more
elements, you should use `(,w ,x . ,_).  I see that the above is
slightly more convenient and concise but I'd value consistency more.

Bye,
Tassilo