How to detect a procedure

How to detect a procedure

[Bruce Korb]

OK.  If:

  (if (procedure? 'mumble) (mumble))

doesn't work, what does?  I keep trying different things
to no avail.  This is very, very frustrating.

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Re: How to detect a procedure

[bitwize]

On Sun, 28 Apr 2002, Bruce Korb wrote:

> 
> OK.  If:
> 
>   (if (procedure? 'mumble) (mumble))
> 
> doesn't work, what does?  I keep trying different things
> to no avail.  This is very, very frustrating.

First of all, this type of thing is better off posted to guile-user 
instead of guile-devel (where nitty-gritty implementation details are 
mainly discussed).

Secondly, the answer to your query is, procedures are stored in the same 
namespace as ordinary variables; (procedure? mumble) returns #t if mumble 
names a prevoiusly defined procedure. There is no need to quote, e.g. 
'mumble, or to use the Common LISP convention #'mumble.

Note that this applies to primitives, too; (procedure? procedure?) returns 
#t. :)

-- 
Jeffrey T. Read
"LOBSTER STICKS TO MAGNET!"


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Re: How to detect a procedure

[rm]

On Mon, Apr 29, 2002 at 06:52:28AM +0200, bitwize@wizards-of-source.org wrote:
> On Sun, 28 Apr 2002, Bruce Korb wrote:
> 
> > 
> > OK.  If:
> > 
> >   (if (procedure? 'mumble) (mumble))
> > 
> > doesn't work, what does?  I keep trying different things
> > to no avail.  This is very, very frustrating.
> 
> First of all, this type of thing is better off posted to guile-user 
> instead of guile-devel (where nitty-gritty implementation details are 
> mainly discussed).
> 
> Secondly, the answer to your query is, procedures are stored in the same 
> namespace as ordinary variables; (procedure? mumble) returns #t if mumble 
> names a prevoiusly defined procedure. There is no need to quote, e.g. 
> 'mumble, or to use the Common LISP convention #'mumble.

Well, there's no need to quote, but if mumble _isn't_ defined than (procedure? mumble)
will barf ... 
The most stable approach would be:

 (and (defined 'blub) (procedure? blub))   

 and the conditional execution could be done like this:

 (if (and (defined 'blub) (procedure? blub)) 
     (blub ...)
     (error "You need a newer version of transmogrify!"))

 Ralf Mattes


> Note that this applies to primitives, too; (procedure? procedure?) returns 
> #t. :)
> 
> -- 
> Jeffrey T. Read
> "LOBSTER STICKS TO MAGNET!"
> 
> 
> _______________________________________________
> Guile-devel mailing list
> Guile-devel@gnu.org
> http://mail.gnu.org/mailman/listinfo/guile-devel

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Re: How to detect a procedure

[Lynn Winebarger]

On Sunday 28 April 2002 23:52, bitwize@wizards-of-source.org wrote:
> On Sun, 28 Apr 2002, Bruce Korb wrote:
> Secondly, the answer to your query is, procedures are stored in the same 
> namespace as ordinary variables; (procedure? mumble) returns #t if mumble 
> names a prevoiusly defined procedure. There is no need to quote, e.g. 
> 'mumble, or to use the Common LISP convention #'mumble.

    I don't think this captures the spirit of the original question.  If you do this,
you rely on the evaluator checking for the existence of the binding - procedure?
gets the actual object (it never sees the name).  Or, if the name hasn't been
bound it will error out (if the lookup throws an exception, that might be used).

Lynn

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Re: How to detect a procedure

[Bruce Korb]

Lynn Winebarger wrote:

> I don't think this captures the spirit of the original question.  If you do this,
> you rely on the evaluator checking for the existence of the binding - procedure?
> gets the actual object (it never sees the name).  Or, if the name hasn't been
> bound it will error out (if the lookup throws an exception, that might be used).

How about adding this procedure.  I confess to being uncertain if it actually
works, I get lost trying to decipher the maze of macros.


SCM_DEFINE (scm_defined_as_p, "defined-as?", 2, 1, 0,
            (SCM sym, SCM class, SCM env),
	    "Return @code{#t} if @var{sym} is defined of class @var{class} in "
	    "the lexical environment @var{env}.  When @var{env} is not "
	    "specified, look in the top-level environment as defined by the "
	    "current module.")
#define FUNC_NAME s_scm_defined_as_p
{
  SCM var;

  SCM_VALIDATE_SYMBOL (1,sym);

  if (SCM_UNBNDP (env))
    var = scm_sym2var (sym, scm_current_module_lookup_closure (),
			 SCM_BOOL_F);
  else
    {
      SCM frames = env;
      register SCM b;
      for (; SCM_NIMP (frames); frames = SCM_CDR (frames))
	{
	  SCM_ASSERT (SCM_CONSP (frames), env, SCM_ARG2, FUNC_NAME);
	  b = SCM_CAR (frames);
	  if (SCM_NFALSEP (scm_procedure_p (b)))
	    break;
	  SCM_ASSERT (SCM_CONSP (b), env, SCM_ARG2, FUNC_NAME);
	  for (b = SCM_CAR (b); SCM_NIMP (b); b = SCM_CDR (b))
	    {
	      if (SCM_NCONSP (b))
		{
		  if (SCM_EQ_P (b, sym))
		    return SCM_BOOL_T;
		  else
		    break;
		}
	      if (SCM_EQ_P (SCM_CAR (b), sym))
		return SCM_BOOL_T;
	    }
	}
      var = scm_sym2var (sym,
			 SCM_NIMP (frames) ? SCM_CAR (frames) : SCM_BOOL_F,
			 SCM_BOOL_F);
    }

  if (SCM_FALSEP (var) || SCM_UNBNDP (SCM_VARIABLE_REF (var)))
    return SCM_BOOL_F;

  if (scm_class_of (SCM_VARIABLE_REF (var)) == class)
    return SCM_BOOL_T;
  return SCM_BOOL_F;
}
#undef FUNC_NAME

==

Bruce Korb <first initial + last name at gnu dot org>
AG URL: http://autogen.sourceforge.net

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Re: How to detect a procedure

[Rob Browning]

Bruce Korb <bkorb@pacbell.net> writes:

> How about adding this procedure.  I confess to being uncertain if it
> actually works, I get lost trying to decipher the maze of macros.

Why this over "defined?"?

Not opposed, just wanted to make sure I understood the intention.

-- 
Rob Browning
rlb @defaultvalue.org, @linuxdevel.com, and @debian.org
Previously @cs.utexas.edu
GPG=1C58 8B2C FB5E 3F64 EA5C  64AE 78FE E5FE F0CB A0AD

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Re: How to detect a procedure

[Bruce Korb]

Rob Browning wrote:

> > How about adding this procedure.  I confess to being uncertain if it
> > actually works, I get lost trying to decipher the maze of macros.
> 
> Why this over "defined?"?
> 
> Not opposed, just wanted to make sure I understood the intention.

The scheme scripts for autogen may be written for a version or
environment where a procedure is defined.  Later, someone may run the
script in another environment without that function.  (e.g., with
a retrograde autogen)  So, yes, ``(defined? 'mumble)'' is probably
adequate.  I don't care a whole lot for "probably adequate".  So,
I would like:

  (defined-as? 'mumble scm_class_procedure)

to be equivalent to:

  (and (defined? 'mumble) (procedure? mumble))

but the latter is conceptually simpler.  I like simple.
It's a more rigorous test (though it can still be fooled).
[[It saves typing two characters, too.  ;-)  **joke!!**]]

A similar scheme could have replaced the myriad of
"procedure?" "pair?" "struct?" "symbol?" ... procedures
so you would automatically have such a function available
for any new class.  Too late now, methinks.

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Re: How to detect a procedure

[Rob Browning]

Bruce Korb <bkorb@pacbell.net> writes:

> I would like:
>
>   (defined-as? 'mumble scm_class_procedure)
>
> to be equivalent to:
>
>   (and (defined? 'mumble) (procedure? mumble))
>
> but the latter is conceptually simpler.  I like simple.

or if you really like the idea of a helper, perhaps (nb: not tested,
or even carefully checked :>):

  (define-macro (defined-as? item predicate)
    `(and (defined? ,item) (,predicate ,item)))

i.e.

  (defined-as? 'mumble procedure?)

-- 
Rob Browning
rlb @defaultvalue.org, @linuxdevel.com, and @debian.org
Previously @cs.utexas.edu
GPG=1C58 8B2C FB5E 3F64 EA5C  64AE 78FE E5FE F0CB A0AD

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Re: How to detect a procedure

[Lynn Winebarger]

On Tuesday 30 April 2002 21:35, Rob Browning wrote:
> Bruce Korb <bkorb@pacbell.net> writes:
> 
> > I would like:
> >
> >   (defined-as? 'mumble scm_class_procedure)
> >
> > to be equivalent to:
> >
> >   (and (defined? 'mumble) (procedure? mumble))
> >
> > but the latter is conceptually simpler.  I like simple.
> 
> or if you really like the idea of a helper, perhaps (nb: not tested,
> or even carefully checked :>):
> 
>   (define-macro (defined-as? item predicate)
>     `(and (defined? ,item) (,predicate ,item)))
> 
> i.e.
> 
>   (defined-as? 'mumble procedure?)

     How about  (defined-as procedure?  'mumble)
to keep the predicate clear?

Lynn

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Re: How to detect a procedure

[Rob Browning]

Lynn Winebarger <owinebar@free-expression.org> writes:

>>   (defined-as? 'mumble procedure?)
>
>      How about  (defined-as procedure?  'mumble)
> to keep the predicate clear?

Looks better to me :>

-- 
Rob Browning
rlb @defaultvalue.org, @linuxdevel.com, and @debian.org
Previously @cs.utexas.edu
GPG=1C58 8B2C FB5E 3F64 EA5C  64AE 78FE E5FE F0CB A0AD

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Re: How to detect a procedure

[Bruce Korb]

Rob Browning wrote:
> 
> Lynn Winebarger <owinebar@free-expression.org> writes:
> 
> >>   (defined-as? 'mumble procedure?)
> >
> >      How about  (defined-as procedure?  'mumble)
> > to keep the predicate clear?
> 
> Looks better to me :>

Me, too :)

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Re: How to detect a procedure

[Neil Jerram]

>>>>> "Bruce" == Bruce Korb <bkorb@pacbell.net> writes:

    Bruce> Rob Browning wrote:
    >> 
    >> Lynn Winebarger <owinebar@free-expression.org> writes:
    >> 
    >> >>   (defined-as? 'mumble procedure?)
    >> >
    >> >      How about  (defined-as procedure?  'mumble)
    >> > to keep the predicate clear?
    >> 
    >> Looks better to me :>

    Bruce> Me, too :)

But I think Rob's definition was missing a quote.

This works for me:

(define-macro (defined-as predicate symbol)
  `(and (defined? ',symbol)
        (,predicate ,symbol)))

guile> (defined-as procedure? procedure?)
#t
guile> (defined-as procedure? does-not-exist)
#f
guile> (defined-as procedure? defined-as)
#f
guile> (defined-as macro? defined-as)
#t
guile> (defined-as procedure? %load-path)
#f
guile> (defined-as list? %load-path)
#t

        Neil


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