X-Git-Url: https://git.hcoop.net/bpt/guile.git/blobdiff_plain/fdc0a82263cb3793cb92d802431162a50f12674c..5b744b67f7f8350bd66d6c0b659f9375a6d700fa:/libguile/boolean.h

diff --git a/libguile/boolean.h b/libguile/boolean.h
index 1388c2fdc..df72728ef 100644
--- a/libguile/boolean.h
+++ b/libguile/boolean.h
@@ -3,21 +3,22 @@
 #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, 2010, 2013 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 2.1 of the License, or (at your option) any later version.
+ * 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
+ * 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
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301 USA
  */
 
 
@@ -26,22 +27,106 @@
 
 
 
-/* Boolean Values 
+/* 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_false(x) scm_is_eq ((x), SCM_BOOL_F)
-#define scm_is_true(x)  !scm_is_false (x)
+#define scm_is_bool(x)   (scm_is_bool_or_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);
 
 
 
+/* 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_API SCM scm_nil_p (SCM obj);
 
 SCM_INTERNAL void scm_init_boolean (void);