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authorMark H Weaver <mhw@netris.org>2009-10-26 23:56:03 +0100
committerAndy Wingo <wingo@pobox.com>2009-10-27 23:25:02 +0100
commit45f4cbdf128c4d3eadcd4bf4571bcc1d61d1039a (patch)
treea9449d5a67ff928a46a800d639401d99fb9b4d89 /libguile/boolean.c
parenta07010bf1828704edd9a40cadb0eaf820b8f3638 (diff)
downloadguile-45f4cbdf128c4d3eadcd4bf4571bcc1d61d1039a.tar.gz
the cube of lisp booleans (#f nil () #t)
* Renumbers the IFLAG constants. * Adds several macros related to boolean type tests, null tests, and boolean-truth testing (including lisp-style boolean-truth tests). * Adds compile-time checks to verify the necessary IFLAG numbering properties needed for the checks to work properly. * Changes some existing code to use the new optimized macros, without changing the semantics of the code at all (except that scm_is_bool is changed from a function to a macro). I added the following macros, whose names explicitly state how %nil should be handled. See the comments in the patch for more information about these. scm_is_false_assume_not_lisp_nil scm_is_true_assume_not_lisp_nil scm_is_false_and_not_lisp_nil scm_is_true_or_lisp_nil scm_is_false_or_lisp_nil scm_is_true_and_not_lisp_nil scm_is_lisp_false scm_is_lisp_true scm_is_null_assume_not_lisp_nil scm_is_null_and_not_lisp_nil scm_is_null_or_lisp_nil scm_is_bool_and_not_lisp_nil scm_is_bool_or_lisp_nil The following already-existing macros are defined as aliases, such that their semantics is unchanged (although scm_is_bool used to be a function and is now a macro). scm_is_null --> scm_is_null_and_not_lisp_nil scm_is_false --> scm_is_false_and_not_lisp_nil scm_is_true --> scm_is_true_or_lisp_nil scm_is_bool --> scm_is_bool_and_not_lisp_nil (I still believe that these should be changed to versions that handle %nil properly, but await approval on that point, so these patches do not make those changes) Also, if the preprocessor macro SCM_ENABLE_ELISP is not true (this macro already existed and was used in lang.h), all overheads associated with %nil handling are eliminated from the above macros. * libguile/tags.h (SCM_BOOL_F, SCM_BOOL_T, SCM_UNSPECIFIED) (SCM_UNDEFINED, SCM_UNBOUND, SCM_ELISP_NIL): Renumber, so that a number of important distinctions (false versus true, end-of-list, etc) can be made by masking a single bit. Also define a number of build-time tests to assert that this condition holds. * libguile/boolean.h (scm_is_false_and_not_nil, scm_is_true_or_nil) (scm_is_false_assume_not_nil, scm_is_true_assume_not_nil): (scm_is_false_or_nil, scm_is_true_and_not_nil) (scm_is_bool_or_nil, scm_is_bool_and_not_nil): New exciting macros to test certain boolean/end-of-list properties. (scm_is_false, scm_is_true): Use a restrictive definition, where only SCM_BOOL_F is false. Should probably change in the future. (scm_is_bool): Incompatible change: changed to be a macro. Was a function before. Probably should allow nil as a boolean, but that will be for a later patch. (scm_is_lisp_false, scm_is_lisp_true): New macros, implementing the standard Lisp boolean predicates, where '() is actually false. * libguile/eval.i.c (CEVAL): Fix a number of false-or-nil and similar tests to use the new macros. * libguile/lang.h (SCM_NULL_OR_NIL_P): Use scm_is_null_or_nil. * libguile/pairs.c: Add a compile-time check that null and nil differ by only one bit. * libguile/pairs.h (scm_is_null_and_not_nil, scm_is_null_assume_not_nil) (scm_is_null_or_nil): New exciting macros! (scm_is_null): Just be scm_is_null_and_not_nil, for now. * libguile/print.c: Adapt to the reordering, and print suitably nasty things for the not-to-be-used values.
Diffstat (limited to 'libguile/boolean.c')
-rw-r--r--libguile/boolean.c35
1 files changed, 26 insertions, 9 deletions
diff --git a/libguile/boolean.c b/libguile/boolean.c
index d79bf7979..d7091bbef 100644
--- a/libguile/boolean.c
+++ b/libguile/boolean.c
@@ -1,4 +1,4 @@
-/* Copyright (C) 1995, 1996, 2000, 2001, 2006, 2008 Free Software Foundation, Inc.
+/* Copyright (C) 1995, 1996, 2000, 2001, 2006, 2008, 2009 Free Software Foundation, Inc.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public License
@@ -29,15 +29,37 @@
#include "libguile/lang.h"
#include "libguile/tags.h"
+#include "verify.h"
+
+/*
+ * These compile-time tests verify the properties needed for the
+ * efficient test macros defined in boolean.h, which are defined in
+ * terms of the SCM_MATCHES_BITS_IN_COMMON macro.
+ *
+ * See the comments preceeding the definitions of SCM_BOOL_F and
+ * SCM_MATCHES_BITS_IN_COMMON in tags.h for more information.
+ */
+verify (SCM_VALUES_DIFFER_IN_EXACTLY_ONE_BIT_POSITION \
+ (SCM_BOOL_F, SCM_BOOL_T));
+verify (SCM_VALUES_DIFFER_IN_EXACTLY_ONE_BIT_POSITION \
+ (SCM_ELISP_NIL, SCM_BOOL_F));
+verify (SCM_VALUES_DIFFER_IN_EXACTLY_ONE_BIT_POSITION \
+ (SCM_ELISP_NIL, SCM_EOL));
+verify (SCM_VALUES_DIFFER_IN_EXACTLY_TWO_BIT_POSITIONS \
+ (SCM_ELISP_NIL, SCM_BOOL_F, SCM_BOOL_T, \
+ SCM_XXX_ANOTHER_BOOLEAN_DONT_USE));
+verify (SCM_VALUES_DIFFER_IN_EXACTLY_TWO_BIT_POSITIONS \
+ (SCM_ELISP_NIL, SCM_BOOL_F, SCM_EOL, \
+ SCM_XXX_ANOTHER_LISP_FALSE_DONT_USE));
SCM_DEFINE (scm_not, "not", 1, 0, 0,
(SCM x),
"Return @code{#t} iff @var{x} is @code{#f}, else return @code{#f}.")
#define FUNC_NAME s_scm_not
{
- return scm_from_bool (scm_is_false (x) || SCM_NILP (x));
+ return scm_from_bool (scm_is_false_or_nil (x));
}
#undef FUNC_NAME
@@ -47,19 +69,14 @@ SCM_DEFINE (scm_boolean_p, "boolean?", 1, 0, 0,
"Return @code{#t} iff @var{obj} is either @code{#t} or @code{#f}.")
#define FUNC_NAME s_scm_boolean_p
{
- return scm_from_bool (scm_is_bool (obj) || SCM_NILP (obj));
+ return scm_from_bool (scm_is_bool_or_nil (obj));
}
#undef FUNC_NAME
int
-scm_is_bool (SCM x)
-{
- return scm_is_eq (x, SCM_BOOL_F) || scm_is_eq (x, SCM_BOOL_T);
-}
-
-int
scm_to_bool (SCM x)
{
+ /* XXX Should this first test use scm_is_false_or_nil instead? */
if (scm_is_eq (x, SCM_BOOL_F))
return 0;
else if (scm_is_eq (x, SCM_BOOL_T))