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the cube of lisp booleans (#f nil () #t)

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* 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.
This commit is contained in:
Mark H Weaver 2009-10-26 23:56:03 +01:00 • committed by Andy Wingo
parent a07010bf18
commit 45f4cbdf12
8 changed files with 256 additions and 41 deletions
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89
libguile/boolean.h
View file

@ -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))
#define scm_is_false(x) scm_is_eq ((x), SCM_BOOL_F)
#define scm_is_true(x) !scm_is_false (x)
/*
* 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))
/* 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);