GNU bug report logs - #22812
24.5: elisp manual about pcase

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Michael Heerdegen <michael_heerdegen <at> web.de>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#22812: closed (24.5: elisp manual about pcase)
Date: Sat, 27 Feb 2016 19:41:01 +0000

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Your message dated Sat, 27 Feb 2016 20:40:12 +0100
with message-id <87wppqkkmb.fsf <at> web.de>
and subject line Re: bug#22812: 24.5: elisp manual about pcase
has caused the debbugs.gnu.org bug report #22812,
regarding 24.5: elisp manual about pcase
to be marked as done.

(If you believe you have received this mail in error, please contact
help-debbugs <at> gnu.org.)


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From: Zhaohui Li <lizhaohui1991 <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 24.5: elisp manual about pcase
Date: Fri, 26 Feb 2016 10:08:09 +0800

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The "10.2.1: Pattern matching case statement" in Emacs Lisp Referrence
Manual has a problem.
The second example in manual is:

>        (defun evaluate (exp env)
>        (pcase exp
>          (`(add ,x ,y)       (+ (evaluate x env) (evaluate y env)))
>          (`(call ,fun ,arg)  (funcall (evaluate fun env) (evaluate arg
> env)))
>          (`(fn ,arg ,body)   (lambda (val)
>                                (evaluate body (cons (cons arg val) env))))
>          ((pred numberp)     exp)
>          ((pred symbolp)     (cdr (assq exp env)))
>          (_                  (error "Unknown expression %S" exp))))
>

The problem is about the third case: `(fn , arg ,body).
I test this function with:

> (evaluate '(call
>             (fn x (add 1 x))
>             2)
>           nil)
>
emcas eval it with throw errors.

I think the correct of this function should be:

> (defun evaluate (exp env)
>   (pcase exp
>     (`(add ,x ,y)
>      (+ (evaluate x env)
>         (evaluate y env)))
>     (`(call ,fun ,arg)
>      (funcall (evaluate fun env)
>               (evaluate arg env)))
>     (`(fn ,arg ,body)
>      `(lambda (val)
>         (evaluate ',body (cons (cons ',arg val) env))))
>     ((pred numberp)
>      exp)
>     ((pred symbolp)
>      (cdr (assq exp env)))
>     (_
>      (error "Unknown expression %S" exp))))
>


Thanks~

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From: Michael Heerdegen <michael_heerdegen <at> web.de>
To: Zhaohui Li <lizhaohui1991 <at> gmail.com>
Cc: 22812-done <at> debbugs.gnu.org
Subject: Re: bug#22812: 24.5: elisp manual about pcase
Date: Sat, 27 Feb 2016 20:40:12 +0100

Ok, the example runs fine with lexical-binding enabled; thanks
nevertheless.  Closing.

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