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/* classes: h_files */
#ifndef SCM_BOOLEAN_H
#define SCM_BOOLEAN_H
/* Copyright (C) 1995,1996,2000, 2006, 2008, 2009, 2010 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
* as published by the Free Software Foundation; either version 3 of
* the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
* 02110-1301 USA
*/
#include "libguile/__scm.h"
/* Boolean Values. Obviously there are #t and #f, but there is also nil to deal
* with. We choose to treat nil as a false boolean. All options might silently
* break existing code, but this one seems most responsible.
*
*/
/*
* 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.
*/
#define scm_is_false_or_nil(x) \
(SCM_MATCHES_BITS_IN_COMMON ((x), SCM_ELISP_NIL, SCM_BOOL_F))
#define scm_is_true_and_not_nil(x) (!scm_is_false_or_nil (x))
/* #nil is false. */
#define scm_is_false(x) (scm_is_false_or_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_0.
* Otherwise, it returns 0.
*/
#define scm_is_bool_or_nil(x) \
(SCM_MATCHES_BITS_IN_COMMON ((x), SCM_BOOL_T, SCM_ELISP_NIL))
#define scm_is_bool_and_not_nil(x) \
(SCM_MATCHES_BITS_IN_COMMON ((x), SCM_BOOL_F, SCM_BOOL_T))
SCM_API int scm_is_bool (SCM);
#define scm_is_bool(x) (scm_is_bool_or_nil (x))
#define scm_from_bool(x) ((x) ? SCM_BOOL_T : SCM_BOOL_F)
SCM_API int scm_to_bool (SCM x);
/* Older spellings for the above routines, kept around for
compatibility. */
#define SCM_FALSEP(x) (scm_is_false (x))
#define SCM_NFALSEP(x) (scm_is_true (x))
#define SCM_BOOLP(x) (scm_is_bool (x))
#define SCM_BOOL(x) (scm_from_bool (x))
#define SCM_NEGATE_BOOL(f) (scm_from_bool (!(f)))
#define SCM_BOOL_NOT(x) (scm_not (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.
*/
#define scm_is_lisp_false(x) \
(SCM_MATCHES_BITS_IN_COMMON ((x), SCM_BOOL_F, SCM_EOL))
SCM_API SCM scm_not (SCM x);
SCM_API SCM scm_boolean_p (SCM obj);
SCM_INTERNAL void scm_init_boolean (void);
#endif /* SCM_BOOLEAN_H */
/*
Local Variables:
c-file-style: "gnu"
End:
*/