Re: pcase bindings in patterns with complicated logic

[Ihor Radchenko <yantar92@posteo.net>]

Thierry Volpiatto <thievol@posteo.net> writes:

>>> [ BTW I don't understand why `app` pattern exists as long as now `pred` is
>>> supporting an extra arg ]
>>
>> Isn't it explained right in the manual?
>>
>> ‘(app FUNCTION PATTERN)’
>>      Matches if FUNCTION called on EXPVAL returns a value that matches
>>      PATTERN.  FUNCTION can take one of the forms described for ‘pred’,
>>      above.  Unlike ‘pred’, however, ‘app’ tests the result against
>>      PATTERN, rather than against a boolean truth value.
>
> Perhaps it is right but I don't understand it, an example in the manual
> would be welcome (if there is one I missed it).

Does this example help?

(pcase '(1 2 3)
  ((app cdr `(2 ,c)) (format "Match: %S" c)))

You cannot easily do the same with pred.

-- 
Ihor Radchenko // yantar92,
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