Re: Instead of pcase

[Philip Kaludercic <philipk@posteo.net>]

Andreas Schwab <schwab@linux-m68k.org> writes:

> On Dez 01 2023, Richard Stallman wrote:
>
>> confusing.  I know what dotted pairs mean, but I was not sure what
>> they meant in pcase patterns.
>
> They don't mean anything.  It's pure lisp syntax.

Right, the doc-string mentions this as well:

--8<---------------cut here---------------start------------->8---
-- `QPAT

Backquote-style pcase patterns: `QPAT
QPAT can take the following forms:
  (QPAT1 . QPAT2)       matches if QPAT1 matches the car and QPAT2 the cdr.
[...]
--8<---------------cut here---------------end--------------->8---

Just like cons-cells are the "real" constituents of a list, so
pattern-matching on a list "really" means pattern matching on
cons-cells.  I believe this is the kind of behaviour that would arise
naturally, whenever someone tries to re-implement this themselves.

As has been said many times already in this thread: All of this seems to
point in the direction that the main issue people are having is that of
documentation, and part of the problem might be that pcase is generating
its doc-string dynamically, which -- while cool -- might not present the
information in the most understandable way.

Another question I meant to raise, and forgive me if I missed it
somewhere in the remaining discussions, is those who find themselves
confused by `pcase':  Do you have experience with programming languages
that heavily rely on pattern matching and/or unification (ML, Haskell,
Prolog, ...)?  Myself having experience with this kind of programming,
all I had to do to understand `pcase' was to translate the existing
abstract notion I had to the syntax that `pcase' provides.  While I can
imagine that one is more prone to be confused, if trying to learn both
the syntax and the point of `pcase', assuming that this kind of
articulating oneself is not natural.