RE: [External] : Re: cond* vs pcase

[Adam Porter <adam@alphapapa.net>]

> It says, in effect, "This just tests the
> value for simple equality (using this or
> that equality predicate)."  It speaks
> quietly, humbly, clearly. >
> `pcase' advertises instead: "Here come the
> Big Guns, which can wrestle _anything_ to
> the ground!  Stand in awe and wonder."

CL-CASE and PCASE neither say nor advertise anything.  They have no 
personal qualities.  They are macros, not people.

   (pcase foo
     ('bar (do-some-bar-stuff))
     ('baz (do-some-baz-fluff)))

is not more awful or wonderful than:

   (cl-case foo
     (bar (do-some-bar-stuff))
     (baz (do-some-baz-fluff)))

And neither of them is worse than what they expand to:

   (cond ((eql foo 'bar)
          (do-some-bar-stuff))
         ((eql foo 'baz)
          (do-some-baz-fluff)))

Nor is this:

   (pcase foo
     (1 'ONE)
     (2 'TWO)
     ((cl-type function) (funcall foo))
     (_ 'SOMETHING-ELSE))

any worse than what it expands to:

   (cond ((eql foo 1)
          'ONE)
         ((eql foo 2)
          'TWO)
         ((cl-typep foo 'function)
          (funcall foo))
         (t
          'SOMETHING-ELSE))

That example is not even a case of pattern-matching, as no patterns are 
involved.

But if one needed to add a pattern, as in the common case of a 
customization option having various possible value types, one may easily 
do so, as in:

   (pcase foo
     (1 'ONE)
     (2 'TWO)
     ((cl-type function) (funcall foo))
     (`(,fn . ,arg) (funcall fn arg))
     (_ 'SOMETHING-ELSE))

I cannot fathom how this optionally available "power" is a problem which 
should consign PCASE to only exceptional cases, any more than Lisp's 
power should consign it to only a few libraries, leaving the rest to be 
implemented in lower-level languages; or any more than Emacs's power 
should consign it to only a few use cases, leaving the the rest to be 
implemented in utilities to be piped together in a shell.