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Re: [PATCH] pcase.el: Add type pattern

From: Adam Porter
Subject: Re: [PATCH] pcase.el: Add type pattern
Date: Tue, 10 Mar 2020 12:03:40 -0500
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux)

Michael Heerdegen <address@hidden> writes:

> Adam Porter <address@hidden> writes:
>> +(pcase-defmacro type (type)
>> +  "Pcase pattern that matches objects of TYPE.
>> +TYPE is a symbol or list as accepted by `cl-typep', which see."
>> +  `(pred (pcase--flip cl-typep ',type)))
>> +
> Is there a reason why you omit the (require 'cl-lib) call in the
> definition as suggested by Stefan?

My understanding was that adding the (require 'cl-lib) form was
suggested if the definition was left in pcase.el, and if the definition
were added to cl-macs.el instead, the (require 'cl-lib) form would not
be needed.  This made sense to me, because cl-macs.el has (require
'cl-lib) at the top of the file.  Of course, I may have misunderstood,
and there are nuances to autoloading and such that I don't fully

> With your definition in emacs -Q:
> (macroexpand-all '(pcase 10 ((type (integer 0 10)) t))) =>
>   (if (cl-typep 10 '(integer 0 10)) (progn t) nil)
> With Stefan's version:
> (macroexpand-all '(pcase 10 ((type (integer 0 10)) t))) =>
>   (if (and (integerp 10) (>= 10 '0) (<= 10 '10)) (progn t) nil)
> I.e. the type expression is treated at compile time and the dependency
> to cl-lib is only at compile time, the compiled code has no dependency.
> That should be better, no?

Of course, that would be better.  However, I was unable to reproduce
those results on my end.  Here are the steps I followed, both on my
main Emacs 26.3 installation and on a build from near master:

1.  Run emacs -Q.
2.  Evaluate this form in *scratch*:

  (pcase-defmacro type (type)
    "Pcase pattern that matches objects of TYPE.
  TYPE is a symbol or list as accepted by `cl-typep', which see."
    `(pred (pcase--flip cl-typep ',type)))

3.  Evaluate this form in *scratch*:

  (macroexpand-all '(pcase 10 ((type (integer 0 10)) t)))


  (if (and (integerp 10) (>= 10 (quote 0)) (<= 10 (quote 10))) (progn t)

I haven't done much work on Emacs's core files before, so I may be doing
something wrong.  Please let me know.  :)

However, I have attached another version of the patch which adds an
autoload for the (pcase-defmacro type) form, which seems proper since
the (pcase-defmacro cl-struct) form in the same file also has one.

Thanks for your help and feedback.

Attachment: 0001-lisp-emacs-lisp-cl-macs.el-Add-type-pattern.patch
Description: Add pcase type pattern, etc.

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