bug#22812: 24.5: elisp manual about pcase

bug#22812: 24.5: elisp manual about pcase

[Zhaohui Li]

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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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bug#22812: 24.5: elisp manual about pcase

[Michael Heerdegen]

Zhaohui Li <lizhaohui1991@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.

bug#22812: 24.5: elisp manual about pcase

[Eli Zaretskii]

> From: Michael Heerdegen <michael_heerdegen@web.de>
> Date: Fri, 26 Feb 2016 14:01:10 +0100
> Cc: 22812@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?

bug#22812: 24.5: elisp manual about pcase

[Michael Heerdegen]

Eli Zaretskii <eliz@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.

bug#22812: 24.5: elisp manual about pcase

[Michael Heerdegen]

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