Re: Question on pcase

["Przemysław Wojnowski" <esperanto@cumego.com>]

W dniu 23.10.2015 o 20:38, Michael Heerdegen pisze:
> I wrote a step by step introduction for people who (1) are frightened by
> `pcase' and (2) are willing to invest some (not much, but some) time to
> learn it.  It is how I would describe `pcase' to a friend, maybe it is
> good for learning, maybe it is ugly, dunno.  Some errors included.
>
> Someone who wants to try to learn pcase (Oleh? Oleh!) can help by
> reading it and telling me if it is understandable, and send corrections
> - or write a better introduction ;-) - and format it nicely for
> inclusion into Elpa or Emacs when it turns out to help people.

Thanks for the tutorial! :-)
I didn't know what pcase is until I read the first few lines. Then I 
just realized that it's just a version of Pattern Matching that I know 
from Clojure (https://youtu.be/mi3OtBc73-k - is a good intro).

Anyway, I read the tutorial and IMHO it is mostly clear. I just have a 
few questions and comments:

line 103:
;; that's the case only for the string "Hallo" (why would it not be
;; useful to leave out the quote before the symbol `a'?

Is it a question to the reader or you just forgot to remove?
---------------
line 136:
;; If matching any pattern established a variable binding, you can
;; refer to these bindings in the following patterns.

Shouldn't end with "[...]the following patterns in the same branch."? 
Without this there's a little confusion on whether the binding is also 
available in the below branches too.
---------------
Around line 177 - (let PAT EXP) example:
(pcase x
   ((and (pred numberp)
         (let (pred (lambda (x) (< 5 x))) (abs x)))
    t)
   (_ nil))
IMHO it would be better to simplify this example to contain only "let" part:
(pcase x
   ((let (pred (lambda (x) (< 5 x))) (abs x))
    t)
   (_ nil))
And in explanation write order of evaluation: result of EXP(x) is passed 
to PAT. Anyway, this part wasn't clear to me.
---------------
What are some good (concrete) use cases for the pcase? When would you 
suggest to use it instead of cond or other similar constructs?
---------------

Great job!

Thanks,
Przemysław