Re: The poor state of documentation of pcase like things.

[Phillip Lord]

Michael Heerdegen <address@hidden> writes:

> address@hidden (Phillip Lord) writes:
>
>> (pcase '(3 1 2)
>>    (`(_ 1 2)
>>    (message "Matched a list of anything followed by (2 3)")))
>>
>> prints nothing.
>>
>> while this...
>>
>> (pcase '(3 1 2)
>>    (`(,_ 1 2)
>>    (message "Matched a list of anything followed by (2 3)")))
>>
>> prints the message (which should be "followed by (2 3)").
>>
>> I am a bit surprised to find that _ needs , in these examples, and I
>> think that it's a bug.
>
> I think it's intentional, and it fits the documentation.

Not convinced. The documentation says....

‘(pred numberp)’ is a pattern that simply checks that ‘exp’ is a number,
and ‘_’ is the catch-all pattern that matches anything.

for example, which made me assume that "_" matches anything.


> We think of elements in a backquoted list to be all quoted unless
> explicitly unquoted.  It makes no sense that '_ matches any expression.
> It matches only the symbol _, and that can be useful, too.

To me it seems unintuitive, to be honest. It took me a while to work
this out; John made the same mistake, it seems.

Phil