bug#20642: 24.5; Please improve documentation for `pcase'

bug#20642: 24.5; Please improve documentation for `pcase'

[Philipp Stephani]

Quoting the documentation of `pcase', some comments inline.

   Perform ML-style pattern matching on EXP.

Users are probably not aware what 'ML-style pattern matching' is.
Please add an introduction without referring to ML.

   CASES is a list of elements of the form (UPATTERN CODE...).

Please document the motivation for the existence and nomenclature or
UPatterns and QPatterns.

    UPatterns can take the following forms:
      _		matches anything.
      SELFQUOTING	matches itself.  This includes keywords,
                        numbers, and strings.

Please add exhaustive information about all the cases covered by the
SELFQUOTING form.  What kinds of forms does it comprise?  There is
overlap with the SYMBOL case below, which has very different semantics,
so the distinction should be made as clear as possible.  Please include
information about the very common symbols nil and t.

      SYMBOL	matches anything and binds it to SYMBOL.

Please state explicitly in which cases this form applies.  Given that _
and :foo are also symbols, it is clear that it doesn't apply to all
symbols.  Something like "all symbols except _, keywords, nil or t"?

      (or UPAT...)	matches if any of the patterns matches.
      (and UPAT...)	matches if all the patterns match.

In the `and' form, please give and example for the following very common
but non-obvious form:

(and UPAT SYMBOL)

e.g. (and (pred integerp) myvar), meaning to bind to a symbol only if
some guard expression matches.




In GNU Emacs 24.5.1 (x86_64-apple-darwin14.1.0, NS apple-appkit-1344.72)
 of 2015-04-12 on p
Configured using:
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Important settings:
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Major mode: Emacs-Lisp

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Recent messages:

Mark set
Sending...
Mark set [2 times]
Sending via mail...
Sending email 
Sending email done
gnutls.c: [0] (Emacs) fatal error: The TLS connection was non-properly terminated.
Sending...done


Load-path shadows:
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Features:
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Memory information:
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bug#20642: 24.5; Please improve documentation for `pcase'

[Stefan Monnier]

>       SELFQUOTING	matches itself.  This includes keywords,
>                         numbers, and strings.
> Please add exhaustive information about all the cases covered by the
> SELFQUOTING form.

Actually, it says it right there: keywords, numbers, and strings.
Admittedly, it doesn't say it's exhaustive (partly because this set
could be expanded in the future, tho at this point it seems unlikely).

>       SYMBOL	matches anything and binds it to SYMBOL.
> Please state explicitly in which cases this form applies.  Given that _
> and :foo are also symbols, it is clear that it doesn't apply to all
> symbols.  Something like "all symbols except _, keywords, nil or t"?

Keywords can't be bound since their value is constant.  Same for nil
and t.  So that should be "obvious enough".  As for _ I think it should
also be obvious enough that between a rule "for _" and rule for "SYMBOL"
the most specific rule should take precedence.


        Stefan

bug#20642: 24.5; Please improve documentation for `pcase'

[Stefan Monnier]

>    Perform ML-style pattern matching on EXP.
> Users are probably not aware what 'ML-style pattern matching' is.

Indeed.  But this "ML-style" is the only useful thing I can think
to add to this first line.  I don't think removing it will help anyone.

> Please add an introduction without referring to ML.

Feel free to suggest a replacement, but remember it has to fit on
a single line.

>    CASES is a list of elements of the form (UPATTERN CODE...).
> Please document the motivation for the existence and nomenclature or
> UPatterns and QPatterns.

In Emacs-25, the docstring has been indirectly modified, so the QPAT now
is only documented in a separate section about the backquote pattern.
You might like to take a look in that version, to see if it makes more
sense that way.


        Stefan

bug#20642: 24.5; Please improve documentation for `pcase'

[Philipp Stephani]

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Stefan Monnier <monnier@iro.umontreal.ca> schrieb am Mo., 25. Mai 2015 um
04:27 Uhr:

> >    Perform ML-style pattern matching on EXP.
> > Users are probably not aware what 'ML-style pattern matching' is.
>
> Indeed.  But this "ML-style" is the only useful thing I can think
> to add to this first line.  I don't think removing it will help anyone.
>
> > Please add an introduction without referring to ML.
>
> Feel free to suggest a replacement, but remember it has to fit on
> a single line.
>
> >    CASES is a list of elements of the form (UPATTERN CODE...).
> > Please document the motivation for the existence and nomenclature or
> > UPatterns and QPatterns.
>
> In Emacs-25, the docstring has been indirectly modified, so the QPAT now
> is only documented in a separate section about the backquote pattern.
> You might like to take a look in that version, to see if it makes more
> sense that way.
>
>
>
I think the current wording is better, thanks.

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bug#20642: 24.5; Please improve documentation for `pcase'

[Philipp Stephani]

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Philipp Stephani <p.stephani2@gmail.com> schrieb am So., 21. Juni 2015 um
15:07 Uhr:

> Stefan Monnier <monnier@iro.umontreal.ca> schrieb am Mo., 25. Mai 2015 um
> 04:27 Uhr:
>
>> >    Perform ML-style pattern matching on EXP.
>> > Users are probably not aware what 'ML-style pattern matching' is.
>>
>> Indeed.  But this "ML-style" is the only useful thing I can think
>> to add to this first line.  I don't think removing it will help anyone.
>>
>> > Please add an introduction without referring to ML.
>>
>> Feel free to suggest a replacement, but remember it has to fit on
>> a single line.
>>
>> >    CASES is a list of elements of the form (UPATTERN CODE...).
>> > Please document the motivation for the existence and nomenclature or
>> > UPatterns and QPatterns.
>>
>> In Emacs-25, the docstring has been indirectly modified, so the QPAT now
>> is only documented in a separate section about the backquote pattern.
>> You might like to take a look in that version, to see if it makes more
>> sense that way.
>>
>>
>>
> I think the current wording is better, thanks.
>

Sorry, wanted to say "the *new* wording (in Emacs 25) is better".

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bug#20642: 24.5; Please improve documentation for `pcase'

[Stefan Monnier]

> Sorry, wanted to say "the *new* wording (in Emacs 25) is better".

Thanks,


        Stefan