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d38b431ace
* libguile/boolean.h (scm_is_false): Recognize nil as false, by default. (scm_is_bool): Recognize nil as a boolean. * libguile/boolean.c (scm_not, scm_boolean, scm_to_bool, scm_is_bool): Adapt to treat nil as false. * libguile/vm-i-system.c (br-if, br-if-not): Just use scm_is_false instead of specifically mentioning nil.
139 lines
4.6 KiB
C
139 lines
4.6 KiB
C
/* classes: h_files */
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#ifndef SCM_BOOLEAN_H
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#define SCM_BOOLEAN_H
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/* Copyright (C) 1995,1996,2000, 2006, 2008, 2009, 2010 Free Software Foundation, Inc.
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public License
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* as published by the Free Software Foundation; either version 3 of
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* the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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* 02110-1301 USA
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*/
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#include "libguile/__scm.h"
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/* Boolean Values. Obviously there are #t and #f, but there is also nil to deal
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* with. We choose to treat nil as a false boolean. All options might silently
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* break existing code, but this one seems most responsible.
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*
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*/
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/*
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* Use these macros if it's important (for correctness)
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* that %nil MUST be considered true
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*/
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#define scm_is_false_and_not_nil(x) (scm_is_eq ((x), SCM_BOOL_F))
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#define scm_is_true_or_nil(x) (!scm_is_eq ((x), SCM_BOOL_F))
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/*
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* Use these macros if %nil will never be tested,
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* for increased efficiency.
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*/
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#define scm_is_false_assume_not_nil(x) (scm_is_eq ((x), SCM_BOOL_F))
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#define scm_is_true_assume_not_nil(x) (!scm_is_eq ((x), SCM_BOOL_F))
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/*
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* See the comments preceeding the definitions of SCM_BOOL_F and
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* SCM_MATCHES_BITS_IN_COMMON in tags.h for more information on
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* how the following macro works.
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*/
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#if SCM_ENABLE_ELISP
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# define scm_is_false_or_nil(x) \
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(SCM_MATCHES_BITS_IN_COMMON ((x), SCM_ELISP_NIL, SCM_BOOL_F))
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#else
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# define scm_is_false_or_nil(x) (scm_is_false_assume_not_nil (x))
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#endif
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#define scm_is_true_and_not_nil(x) (!scm_is_false_or_nil (x))
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/* %nil is false. */
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#define scm_is_false(x) (scm_is_false_or_nil (x))
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#define scm_is_true(x) (!scm_is_false (x))
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/*
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* Since we know SCM_BOOL_F and SCM_BOOL_T differ by exactly one bit,
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* and that SCM_BOOL_F and SCM_ELISP_NIL differ by exactly one bit,
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* and that they of course can't be the same bit (or else SCM_BOOL_T
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* and SCM_ELISP_NIL be would equal), it follows that SCM_BOOL_T and
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* SCM_ELISP_NIL differ by exactly two bits, and these are the bits
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* which will be ignored by SCM_MATCHES_BITS_IN_COMMON below.
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*
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* See the comments preceeding the definitions of SCM_BOOL_F and
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* SCM_MATCHES_BITS_IN_COMMON in tags.h for more information.
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*
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* If SCM_ENABLE_ELISP is true, then scm_is_bool_or_nil(x)
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* returns 1 if and only if x is one of the following: SCM_BOOL_F,
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* SCM_BOOL_T, SCM_ELISP_NIL, or SCM_XXX_ANOTHER_BOOLEAN_DONT_USE_0.
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* Otherwise, it returns 0.
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*/
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#if SCM_ENABLE_ELISP
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# define scm_is_bool_or_nil(x) \
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(SCM_MATCHES_BITS_IN_COMMON ((x), SCM_BOOL_T, SCM_ELISP_NIL))
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#else
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# define scm_is_bool_or_nil(x) (scm_is_bool_and_not_nil (x))
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#endif
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#define scm_is_bool_and_not_nil(x) \
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(SCM_MATCHES_BITS_IN_COMMON ((x), SCM_BOOL_F, SCM_BOOL_T))
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SCM_API int scm_is_bool (SCM);
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#define scm_is_bool(x) (scm_is_bool_or_nil (x))
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#define scm_from_bool(x) ((x) ? SCM_BOOL_T : SCM_BOOL_F)
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SCM_API int scm_to_bool (SCM x);
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/*
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* The following macros efficiently implement boolean truth testing as
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* expected by most lisps, which treat '() aka SCM_EOL as false.
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*
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* Since we know SCM_ELISP_NIL and SCM_BOOL_F differ by exactly one
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* bit, and that SCM_ELISP_NIL and SCM_EOL differ by exactly one bit,
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* and that they of course can't be the same bit (or else SCM_BOOL_F
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* and SCM_EOL be would equal), it follows that SCM_BOOL_F and SCM_EOL
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* differ by exactly two bits, and these are the bits which will be
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* ignored by SCM_MATCHES_BITS_IN_COMMON below.
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*
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* See the comments preceeding the definitions of SCM_BOOL_F and
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* SCM_MATCHES_BITS_IN_COMMON in tags.h for more information.
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*
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* scm_is_lisp_false(x) returns 1 if and only if x is one of the
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* following: SCM_BOOL_F, SCM_ELISP_NIL, SCM_EOL or
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* SCM_XXX_ANOTHER_LISP_FALSE_DONT_USE. Otherwise, it returns 0.
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*/
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#if SCM_ENABLE_ELISP
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# define scm_is_lisp_false(x) \
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(SCM_MATCHES_BITS_IN_COMMON ((x), SCM_BOOL_F, SCM_EOL))
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# define scm_is_lisp_true(x) (!scm_is_lisp_false(x))
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#endif
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SCM_API SCM scm_not (SCM x);
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SCM_API SCM scm_boolean_p (SCM obj);
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SCM_INTERNAL void scm_init_boolean (void);
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#endif /* SCM_BOOLEAN_H */
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/*
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Local Variables:
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c-file-style: "gnu"
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End:
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*/
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