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Re: Unifying properties
Marius Vollmer <mvo@zagadka.ping.de> writes:
> So, we should probably design some helper functions for doing the job
> of properties, but in a more modern way. What about:
>
> Function: make-object-property
Ok, I have implemented this. I will check it in after the repository
has been thawed again.
I did it in two layers: some `primitive' functions in C that have a
more involved and explicit interface, and a simple wrapper that
implements `make-object-property' on top of this.
The lower layer has an additional feature: you can specify a
not-found-proc that will lazily compute a default value for a missing
property. I intend to use this for things like the 'arity property of
procedures or other properties that might be expensive to compute.
/* Copyright (C) 1995,1996, 2000 Free Software Foundation, Inc.
*
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* for additional uses of the text contained in its release of GUILE.
*
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* to produce an executable, this does not by itself cause the
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/* Software engineering face-lift by Greg J. Badros, 11-Dec-1999,
gjb@cs.washington.edu, http://www.cs.washington.edu/homes/gjb */
#include <stdio.h>
#include "libguile/_scm.h"
#include "libguile/hashtab.h"
#include "libguile/alist.h"
#include "libguile/root.h"
#include "libguile/weaks.h"
#include "libguile/validate.h"
#include "libguile/eval.h"
#include "libguile/properties.h"
/* {Properties}
*/
SCM_DEFINE (scm_primitive_make_property, "primitive-make-property", 1, 0, 0,
(SCM not_found_proc),
"Create a @dfn{property token} that can be used with\n"
"@code{primitive-property-ref} and @code{primitive-property-set!}.\n"
"See @code{primitive-property-ref} for the significance of\n"
"@var{not_found_proc}.")
#define FUNC_NAME s_scm_primitive_make_property
{
if (not_found_proc != SCM_BOOL_F)
SCM_VALIDATE_PROC (SCM_ARG1, not_found_proc);
return scm_cons (not_found_proc, SCM_EOL);
}
#undef FUNC_NAME
SCM_DEFINE (scm_primitive_property_ref, "primitive-property-ref", 2, 0, 0,
(SCM prop, SCM obj),
"Return the property @var{prop} of @var{obj}. When no value\n"
"has yet been associated with @var{prop} and @var{obj}, call\n"
"@var{not-found-proc} instead (see @code{primitive-make-property})\n"
"and use its return value. That value is also associated with\n"
"@var{obj} via @code{primitive-property-set!}. When\n"
"@var{not-found-proc} is @code{#f}, use @code{#f} as the\n"
"default value of @var{prop}.")
#define FUNC_NAME s_scm_primitive_property_ref
{
SCM h, assoc;
SCM_VALIDATE_CONS (SCM_ARG1, prop);
h = scm_hashq_get_handle (scm_properties_whash, obj);
assoc = (SCM_NIMP (h) ? scm_assq (prop, SCM_CDR (h)) : SCM_BOOL_F);
if (SCM_NIMP (assoc))
return SCM_CDR (assoc);
if (SCM_FALSEP (SCM_CAR (prop)))
return SCM_BOOL_F;
else
{
SCM val = scm_apply (SCM_CAR (prop),
SCM_LIST2 (prop, obj), SCM_EOL);
if (SCM_IMP (h))
h = scm_hashq_create_handle_x (scm_properties_whash, obj, SCM_EOL);
SCM_SETCDR (h, scm_acons (prop, val, SCM_CDR (h)));
return val;
}
}
#undef FUNC_NAME
SCM_DEFINE (scm_primitive_property_set_x, "primitive-property-set!", 3, 0, 0,
(SCM prop, SCM obj, SCM val),
"Associate @var{code} with @var{prop} and @var{obj}.")
#define FUNC_NAME s_scm_primitive_property_set_x
{
SCM h, assoc;
SCM_VALIDATE_CONS (SCM_ARG1, prop);
h = scm_hashq_create_handle_x (scm_properties_whash, obj, SCM_EOL);
assoc = scm_assq (prop, SCM_CDR (h));
if (SCM_NIMP (assoc))
SCM_SETCDR (assoc, val);
else
{
assoc = scm_acons (prop, val, SCM_CDR (h));
SCM_SETCDR (h, assoc);
}
return SCM_UNSPECIFIED;
}
#undef FUNC_NAME
SCM_DEFINE (scm_primitive_property_del_x, "primitive-property-del!", 2, 0, 0,
(SCM prop, SCM obj),
"Remove any value associated with @var{prop} and @var{obj}.")
#define FUNC_NAME s_scm_primitive_property_del_x
{
SCM h;
SCM_VALIDATE_CONS (SCM_ARG1, prop);
h = scm_hashq_get_handle (scm_properties_whash, obj);
if (SCM_NIMP (h))
SCM_SETCDR (h, scm_assq_remove_x (SCM_CDR (h), prop));
return SCM_UNSPECIFIED;
}
#undef FUNC_NAME
void
scm_init_properties ()
{
scm_properties_whash = scm_make_weak_key_hash_table (SCM_MAKINUM (511));
#include "libguile/properties.x"
}
/*
Local Variables:
c-file-style: "gnu"
End:
*/