Re: A protest against pcase, pcase-let, pcase-let*

[Dmitry Gutov <dgutov@yandex.ru>]

On 03/31/2015 09:00 PM, Alan Mackenzie wrote:

> OK, maybe pcase itself has a page in the elisp manual, but this page is
> very difficult to understand, certainly for me.  I have attempted quite
> a lot of times to make sense of it, and failed.

I think it's pretty nice. It provides pattern matching, as well as 
destructuring (something that previously required the use of cl-lib), in 
a concise and performant way.

The docs can look a bit dense at first, but after reading them carefully 
and experimenting a bit, I'm sure most people can get a hang of it.

> There are two possibilities here: (i) the page is difficult because
> pcase is itself difficult.

It's not trivial. Pattern matching is, usually, a feature of more 
advanced programming languages. But that doesn't mean we shouldn't use it.

> pcase-let and pcase-let* are totally absent from the elisp manual.
> Their doc strings say nothing more than "Like `let' but where you can
> use `pcase' patterns for bindings.", without giving any clue as to what
> "`pcase' patterns" are, or what the syntax and semantics of their
> "use" of them for bindings look like.

`pcase' patterns are described in the `pcase' docstring, and in the 
manual entry for it.

The semantics of use of them for bindings should be pretty apparent 
after you understand how to use `pcase' itself.

> As an aside, I suspect that edebug will not be useful in (possibly
> large) uses of these forms, given that they are implemented as macros
> rather than special forms.

It worked well when I tried it.