Re: Instead of pcase

[Dmitry Gutov <dmitry@gutov.dev>]

On 04/12/2023 13:58, Eli Zaretskii wrote:
>> From: Richard Stallman<rms@gnu.org>
>> Cc:emacs-devel@gnu.org
>> Date: Sun, 03 Dec 2023 22:08:21 -0500
>>
>>    > This is not true.  There is no magic at all in the use of this reader
>>    > feature which is totally lost after reading.  It is absolutely
>>    > impossible to detect its use afterwards.
>>
>> As a factual matter about dotted pairs in pcase patterns, that is
>> correct.
>>
>> However, we have repeatedly seen that experienced Lispers, who would
>> have no trouble understanding those constructs in a backquote meant to
>> actually construct a structure of conses, don't know what to make of
>> them on encountering them in pcase patterns.
>>
>> That's another factual matter about dotted pairs in pcase patterns.
>> It is more a psychological matter than a computational matter, but
>> that doesn't invalidate the observation.
>>
>> It is part of the impact of complexity of pcase.
> Some people are saying that everything is clear because the Lisp
> reader does this and that.  But when humans read code, they don't
> normally run the Lisp reader in their head, they use other techniques
> to read and grasp what the code does.  If there's a need to ask what
> does the Lisp reader do with some syntax, that is already an obstacle
> to understanding the code, even though eventually one can understand
> it, whether by thinking what the reader does or by actually running
> the reader and/or macro-expansion.

Note that this subthread is not about pcase but about a particular 
instance where it was used together with the dotted syntax. In other 
places, people would use the dotted reader syntax inside a backquote 
without pcase, and the above considerations would stil apply.

Finally, in the example that was brought up, the dot syntax really *was* 
used to make comprehension more easy. But to see that you have to 
actually read the surrounding code and try to understand the data flow. 
And if the dotted syntax were not used, the spectator *would* have to 
conjure up the knowledge that (a . (b c)) is the same as (a b c). 
Whereas the current solution avoids that need.