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

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

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

[Message part 1 (text/plain, inline)]

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~

[Message part 2 (text/html, inline)]

Message #8 received at 22812 <at> debbugs.gnu.org (full text, mbox):

From: Michael Heerdegen <michael_heerdegen <at> web.de>
To: Zhaohui Li <lizhaohui1991 <at> gmail.com>
Cc: 22812 <at> debbugs.gnu.org
Subject: Re: bug#22812: 24.5: elisp manual about pcase
Date: Fri, 26 Feb 2016 14:01:10 +0100

Zhaohui Li <lizhaohui1991 <at> gmail.com> writes:

> 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. 

Works for me.  Did you enable lexical binding when testing?


Regards,

Michael.

Message #11 received at 22812 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Michael Heerdegen <michael_heerdegen <at> web.de>
Cc: 22812 <at> debbugs.gnu.org, lizhaohui1991 <at> gmail.com
Subject: Re: bug#22812: 24.5: elisp manual about pcase
Date: Fri, 26 Feb 2016 17:43:23 +0200

> From: Michael Heerdegen <michael_heerdegen <at> web.de>
> Date: Fri, 26 Feb 2016 14:01:10 +0100
> Cc: 22812 <at> debbugs.gnu.org
> 
> >  (evaluate '(call
> >  (fn x (add 1 x))
> >  2)
> >  nil)
> >
> >
> > emcas eval it with throw errors. 
> 
> Works for me.  Did you enable lexical binding when testing?

Should we add a comment to the manual with this caveat?

Message #14 received at 22812 <at> debbugs.gnu.org (full text, mbox):

From: Michael Heerdegen <michael_heerdegen <at> web.de>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 22812 <at> debbugs.gnu.org, lizhaohui1991 <at> gmail.com
Subject: Re: bug#22812: 24.5: elisp manual about pcase
Date: Fri, 26 Feb 2016 17:30:07 +0100

Eli Zaretskii <eliz <at> gnu.org> writes:

> > Works for me.  Did you enable lexical binding when testing?
>
> Should we add a comment to the manual with this caveat?

There is one, quite before the example:

> Here is an example of using ‘pcase’ to implement a simple interpreter
> for a little expression language (note that this example requires
> lexical binding, *note Lexical Binding::): [...]


Michael.

Message #19 received at 22812-done <at> debbugs.gnu.org (full text, mbox):

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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