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author | Mark H Weaver <mhw@netris.org> | 2009-10-26 23:56:03 +0100 |
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committer | Andy Wingo <wingo@pobox.com> | 2009-10-27 23:25:02 +0100 |
commit | 45f4cbdf128c4d3eadcd4bf4571bcc1d61d1039a (patch) | |
tree | a9449d5a67ff928a46a800d639401d99fb9b4d89 /libguile/boolean.h | |
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.h')
-rw-r--r-- | libguile/boolean.h | 89 |
1 files changed, 85 insertions, 4 deletions
diff --git a/libguile/boolean.h b/libguile/boolean.h index 5a8379713..4c97a4933 100644 --- a/libguile/boolean.h +++ b/libguile/boolean.h @@ -3,7 +3,7 @@ #ifndef SCM_BOOLEAN_H #define SCM_BOOLEAN_H -/* Copyright (C) 1995,1996,2000, 2006, 2008 Free Software Foundation, Inc. +/* Copyright (C) 1995,1996,2000, 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 @@ -31,16 +31,97 @@ * */ +/* + * Use these macros if it's important (for correctness) + * that %nil MUST be considered true + */ +#define scm_is_false_and_not_nil(x) (scm_is_eq ((x), SCM_BOOL_F)) +#define scm_is_true_or_nil(x) (!scm_is_eq ((x), SCM_BOOL_F)) + +/* + * Use these macros if %nil will never be tested, + * for increased efficiency. + */ +#define scm_is_false_assume_not_nil(x) (scm_is_eq ((x), SCM_BOOL_F)) +#define scm_is_true_assume_not_nil(x) (!scm_is_eq ((x), SCM_BOOL_F)) + +/* + * See the comments preceeding the definitions of SCM_BOOL_F and + * SCM_MATCHES_BITS_IN_COMMON in tags.h for more information on + * how the following macro works. + */ +#if SCM_ENABLE_ELISP +# define scm_is_false_or_nil(x) \ + (SCM_MATCHES_BITS_IN_COMMON ((x), SCM_ELISP_NIL, SCM_BOOL_F)) +#else +# define scm_is_false_or_nil(x) (scm_is_false_assume_not_nil (x)) +#endif +#define scm_is_true_and_not_nil(x) (!scm_is_false_or_nil (x)) -#define scm_is_false(x) scm_is_eq ((x), SCM_BOOL_F) -#define scm_is_true(x) !scm_is_false (x) +/* XXX Should these macros treat %nil as false by default? */ +#define scm_is_false(x) (scm_is_false_and_not_nil (x)) +#define scm_is_true(x) (!scm_is_false (x)) + +/* + * Since we know SCM_BOOL_F and SCM_BOOL_T differ by exactly one bit, + * and that SCM_BOOL_F and SCM_ELISP_NIL differ by exactly one bit, + * and that they of course can't be the same bit (or else SCM_BOOL_T + * and SCM_ELISP_NIL be would equal), it follows that SCM_BOOL_T and + * SCM_ELISP_NIL differ by exactly two bits, and these are the bits + * which will be ignored by SCM_MATCHES_BITS_IN_COMMON below. + * + * See the comments preceeding the definitions of SCM_BOOL_F and + * SCM_MATCHES_BITS_IN_COMMON in tags.h for more information. + * + * If SCM_ENABLE_ELISP is true, then scm_is_bool_or_nil(x) + * returns 1 if and only if x is one of the following: SCM_BOOL_F, + * SCM_BOOL_T, SCM_ELISP_NIL, or SCM_XXX_ANOTHER_BOOLEAN_DONT_USE. + * Otherwise, it returns 0. + */ +#if SCM_ENABLE_ELISP +# define scm_is_bool_or_nil(x) \ + (SCM_MATCHES_BITS_IN_COMMON ((x), SCM_BOOL_T, SCM_ELISP_NIL)) +#else +# define scm_is_bool_or_nil(x) (scm_is_bool_and_not_nil (x)) +#endif + +#define scm_is_bool_and_not_nil(x) \ + (SCM_MATCHES_BITS_IN_COMMON ((x), SCM_BOOL_F, SCM_BOOL_T)) + +/* XXX Should scm_is_bool treat %nil as a boolean? */ +#define scm_is_bool(x) (scm_is_bool_and_not_nil (x)) -SCM_API int scm_is_bool (SCM x); #define scm_from_bool(x) ((x) ? SCM_BOOL_T : SCM_BOOL_F) SCM_API int scm_to_bool (SCM x); +/* + * The following macros efficiently implement boolean truth testing as + * expected by most lisps, which treat '() aka SCM_EOL as false. + * + * Since we know SCM_ELISP_NIL and SCM_BOOL_F differ by exactly one + * bit, and that SCM_ELISP_NIL and SCM_EOL differ by exactly one bit, + * and that they of course can't be the same bit (or else SCM_BOOL_F + * and SCM_EOL be would equal), it follows that SCM_BOOL_F and SCM_EOL + * differ by exactly two bits, and these are the bits which will be + * ignored by SCM_MATCHES_BITS_IN_COMMON below. + * + * See the comments preceeding the definitions of SCM_BOOL_F and + * SCM_MATCHES_BITS_IN_COMMON in tags.h for more information. + * + * scm_is_lisp_false(x) returns 1 if and only if x is one of the + * following: SCM_BOOL_F, SCM_ELISP_NIL, SCM_EOL or + * SCM_XXX_ANOTHER_LISP_FALSE_DONT_USE. Otherwise, it returns 0. + */ +#if SCM_ENABLE_ELISP +# define scm_is_lisp_false(x) \ + (SCM_MATCHES_BITS_IN_COMMON ((x), SCM_BOOL_F, SCM_EOL)) +# define scm_is_lisp_true(x) (!scm_is_lisp_false(x)) +#endif + + + SCM_API SCM scm_not (SCM x); SCM_API SCM scm_boolean_p (SCM obj); |