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author | Mark H Weaver <mhw@netris.org> | 2009-10-26 23:56:03 +0100 |
---|---|---|
committer | Andy Wingo <wingo@pobox.com> | 2009-10-27 23:25:02 +0100 |
commit | 45f4cbdf128c4d3eadcd4bf4571bcc1d61d1039a (patch) | |
tree | a9449d5a67ff928a46a800d639401d99fb9b4d89 /libguile/boolean.c | |
parent | a07010bf1828704edd9a40cadb0eaf820b8f3638 (diff) | |
download | guile-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.c | 35 |
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)) |