Re: pcase defuns

[Andrew Hyatt]

On Tue, Dec 21, 2021 at 11:18 PM Richard Stallman <rms@gnu.org> 
wrote: 

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>   > I agree that just implementing everything in a function is 
>   > reasonable.  For that, just using pcase seems good enough, 
>   > although it might be interesting to have a very different 
>   > way of  writing a function such as 
>
>   > (pcase-defun mytest 
>   >   "Demonstrates a way of writing defuns via pcase matching." 
>   >   ((a b _) "a b match") (`(c ,v _) (format "c %s match" v))) 
>
> This avoids the split-up-definition problems I was talking 
> about, since it is all in one place with one name. 
>
> Please make the defining form's name follow th convention of 
> starting with `def', so people and tools will recognize that it 
> is a defining form. 
>
> Also, why use `pcase' in the name?  According to the docs of 
> `pcase', this pattern matching is not similar.

This really is the same as pcase, with some transformation to make 
the backquote-style and other style equivalent. For example, the 
above would translate to:

(pcase val
      ((seq 'a 'b _) "a b match")
      (`(c ,v ,_) (format "c %s match" v)))

I think we could probably just use pcase style, but I wanted to 
make the style more consistent between backquote and normal pcase 
matching.  For example, backquote matching can match a sequence of 
matches, but normal matching would require the "seq" matcher at 
the start to do the same thing.

It could be that the way I transform these can be improved, in 
fact, maybe the following would be better:

(def-pcase mytest 
  "Demonstrates a way of writing defuns via pcase matching." 
  (('a 'b '_) "a b match") (('c v '_) (format "c %s match" v)))

Or, as you say, perhaps if we use the name pcase we should just be 
completely consistent with how pcase does things, and not to make 
it more internally self-consistent.

> --
> Dr Richard Stallman (https://stallman.org)
> Chief GNUisance of the GNU Project (https://gnu.org)
> Founder, Free Software Foundation (https://fsf.org)
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