Re: Replace trivial pcase occurrences in the Emacs sources

[Michael Heerdegen]

Eli Zaretskii <address@hidden> writes:

> > (pcase '(1 2 3)
> >   ((let a 3) a))
> > ==> 3
>
> Thanks, but I meant an example of what's described after the "OTOH".

Oh, sorry.  How about this:

(defun second-elt-is-positive-p (l)
    (pcase l
      (`(,_ ,(pred (< 0)) . ,_) t)))

(second-elt-is-positive-p (list 1 2 3))
==> t

(second-elt-is-positive-p (list 1 -2 3))
==> nil

Is the pattern `(,_ ,(pred (< 0)) . ,_) destructuring or does it
additionally have to bind at least one variable to be called like that?

Such patterns are used in real life - some bind variables, but others
are only used as tests to see if the structure fulfils certain
requirements.  I guess there is no sharp dividing line.


Michael.