testing arity

testing arity

[Jon Wilson]

Hi,
Is there a good way to determine the number of arguments that a given 
procedure will take?  I suppose I can look at
(source proc)
and extract the list of formals, and write a procedure which does this 
automatically, but I'd hate to reinvent the wheel.  Also, I'm not sure how 
well using source will work when we have optional or keyword arguments.

Also, on an unrelated note, is it possible to define values (as in (lambda 
() (values 1 2)) ) in terms of McCarthy's original seven lisp primitives? 
Or would this question be better asked somewhere else (like c.l.scheme)?
Regards,
Jon


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Re: testing arity

[rm]

On Sat, Jul 22, 2006 at 11:19:28AM -0500, Jon Wilson wrote:
> Hi,
> Is there a good way to determine the number of arguments that a given 
> procedure will take?  I suppose I can look at
> (source proc)
> and extract the list of formals, and write a procedure which does this 
> automatically, but I'd hate to reinvent the wheel.  Also, I'm not sure how 
> well using source will work when we have optional or keyword arguments.

What doesn't work with 'arity'?

guile> (define (myne n m) (* n m))
guile> (arity myne)
2 arguments: `n' and `m'. 


 Cheers, Ralf Mattes
    
> Also, on an unrelated note, is it possible to define values (as in (lambda 
> () (values 1 2)) ) in terms of McCarthy's original seven lisp primitives? 
> Or would this question be better asked somewhere else (like c.l.scheme)?
> Regards,
> Jon
> 
> 
> _______________________________________________
> Guile-user mailing list
> Guile-user@gnu.org
> http://lists.gnu.org/mailman/listinfo/guile-user



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Re: testing arity

[Jon Wilson]

Hi Ralf,

rm@tuxteam.de wrote:

> What doesn't work with 'arity'?

Ah.  The answer to that question is "It is not documented in the guile 
manual, nor in R5RS.".

Regards,
Jon


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Re: testing arity

[tomas]

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On Sat, Jul 22, 2006 at 11:19:28AM -0500, Jon Wilson wrote:
> Hi,
> Is there a good way to determine the number of arguments that a given 
> procedure will take?

Here's a fishing rod ;-)

 | tomas@herr-turtur:~$ guile
 | guile> (apropos "arity")
 | (ice-9 session): arity  #<procedure arity (obj)>
 | guile> (arity apropos)
 | 1 or more arguments: `rgx', the rest in `options'.
 | guile> 

> Also, on an unrelated note, is it possible to define values (as in (lambda 
> () (values 1 2)) ) in terms of McCarthy's original seven lisp primitives? 
> Or would this question be better asked somewhere else (like c.l.scheme)?

I don't understand exactly what you mean here. There is values and
call-with-values in guile -- but maybe my answer is way off...

Regards
-- toms

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Re: testing arity

[Neil Jerram]

tomas@tuxteam.de writes:

> On Sat, Jul 22, 2006 at 11:19:28AM -0500, Jon Wilson wrote:
>> Hi,
>> Is there a good way to determine the number of arguments that a given 
>> procedure will take?
>
> Here's a fishing rod ;-)
>
>  | tomas@herr-turtur:~$ guile
>  | guile> (apropos "arity")
>  | (ice-9 session): arity  #<procedure arity (obj)>
>  | guile> (arity apropos)
>  | 1 or more arguments: `rgx', the rest in `options'.
>  | guile> 

And if you're not keen on parsing arity's output, see its definition
in (ice-9 session) for the procedure properties that it queries to
produce this.

>> Also, on an unrelated note, is it possible to define values (as in (lambda 
>> () (values 1 2)) ) in terms of McCarthy's original seven lisp primitives? 
>> Or would this question be better asked somewhere else (like c.l.scheme)?

Yes, sounds to me like a question for c.l.scheme.

Regards,
     Neil



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Re: testing arity

[Kevin Ryde]

Neil Jerram <neil@ossau.uklinux.net> writes:
>
> And if you're not keen on parsing arity's output, see its definition
> in (ice-9 session) for the procedure properties that it queries to
> produce this.

(procedure-property obj 'arity) being the operative part, it gives a
list of "(required-count optional-count more?)".  "required-count"
many arguments required, plus up to "optional-count" further, or if
the "more?" flag is #t then an arbitrary number more.

I've been using it in my lint program (gratuitous plug).  A few funcs
defined in scheme code take "(foo bar . rest)" style rather than have
an "optional-count", eg. `atan'.


http://www.geocities.com/user42_kevin/guile-lint/index.html


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Re: testing arity

[Jon Wilson]

Thanks, Neil.  Sounds like an excellent answer!
Regards,
Jon

Neil Jerram wrote:
> tomas@tuxteam.de writes:
> 
> 
>>On Sat, Jul 22, 2006 at 11:19:28AM -0500, Jon Wilson wrote:
>>
>>>Hi,
>>>Is there a good way to determine the number of arguments that a given 
>>>procedure will take?
>>
>>Here's a fishing rod ;-)
>>
>> | tomas@herr-turtur:~$ guile
>> | guile> (apropos "arity")
>> | (ice-9 session): arity  #<procedure arity (obj)>
>> | guile> (arity apropos)
>> | 1 or more arguments: `rgx', the rest in `options'.
>> | guile> 
> 
> 
> And if you're not keen on parsing arity's output, see its definition
> in (ice-9 session) for the procedure properties that it queries to
> produce this.
> 
> 
>>>Also, on an unrelated note, is it possible to define values (as in (lambda 
>>>() (values 1 2)) ) in terms of McCarthy's original seven lisp primitives? 
>>>Or would this question be better asked somewhere else (like c.l.scheme)?
> 
> 
> Yes, sounds to me like a question for c.l.scheme.
> 
> Regards,
>      Neil
> 



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