bug#16201: 24.3.50; error expanding pcase with a pred clause

bug#16201: 24.3.50; error expanding pcase with a pred clause

[Michael Heerdegen]

Hi,

sorry if this is a known issue.

In emacs -Q (current trunk), save the following snipped

--8<---------------cut here---------------start------------->8---
(require 'pcase)

(defun test-buffer-file-name ()
  (pcase buffer-file-name
    (`nil                   'not-a-file)
    ((pred file-writable-p) 'writable)
    (_                      'not-writable)))
--8<---------------cut here---------------end--------------->8---

into a file.  Then, M-: (byte-compile-file buffer-file-name).  You get
an error:

  pcase-bug.el:3:1:Error: Wrong type argument: stringp, nil

Same with C-x C-e with point after the defun.

BTW, (require 'pcase) is necessary in the recipe.  If pcase has not yet
been loaded, the error doesn't happen.  Instead you can compile or eval
the defun (once), and it works as expected!


Thanks,

Michael.




In GNU Emacs 24.3.50.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.8.4)
 of 2013-12-20 on drachen
Windowing system distributor `The X.Org Foundation', version 11.0.11403000
System Description:	Debian GNU/Linux testing (jessie)

Configured using:
 `configure --prefix=/usr/local/built/'

Important settings:
  value of $LC_ALL: de_DE.utf8
  value of $LC_COLLATE: C
  value of $LC_TIME: C
  value of $LANG: de_DE.utf8
  locale-coding-system: utf-8-unix

Major mode: Emacs-Lisp

bug#16201: 24.3.50; error expanding pcase with a pred clause

[Michael Heerdegen]

Michael Heerdegen <michael_heerdegen@web.de> writes:


> (defun test-buffer-file-name ()
>   (pcase buffer-file-name
>     (`nil                   'not-a-file)
>     ((pred file-writable-p) 'writable)
>     (_                      'not-writable)))
>
>   pcase-bug.el:3:1:Error: Wrong type argument: stringp, nil

pcase seems to test whether the constant (nil) from the first clause
fulfills the pred of the second clause.  Which is not legal in this
case.

I thought this could be ok:

(pcase buffer-file-name
    (`nil                   'not-a-file)
    ((and (pred stringp)
	  (pred file-writable-p)) 'writable)
    (_                      'not-writable))

but that triggers the same error.

This works, however, but doesn't look so nice:

  (pcase buffer-file-name
    (`nil                   'not-a-file)
    ((pred (lambda (x) (and (stringp x) (file-writable-p x)))) 'writable)
    (_                      'not-writable))


Regards,

Michael.

bug#16201: 24.3.50; error expanding pcase with a pred clause

[Stefan Monnier]

> sorry if this is a known issue.

It wasn't, thank you.

>   pcase-bug.el:3:1:Error: Wrong type argument: stringp, nil

Should be fixed now, thank you,


        Stefan