doc/ref/api-smobs.texi

   1 @c -*-texinfo-*-
   2 @c This is part of the GNU Guile Reference Manual.
   3 @c Copyright (C)  1996, 1997, 2000, 2001, 2002, 2003, 2004
   4 @c   Free Software Foundation, Inc.
   5 @c See the file guile.texi for copying conditions.
   6
   7 @page
   8 @node Smobs
   9 @section Smobs
  10
  11 This chapter contains reference information related to defining and
  12 working with smobs.  See @ref{Defining New Types (Smobs)} for a
  13 tutorial-like introduction to smobs.
  14
  15 @deftypefun scm_t_bits scm_make_smob_type (const char *name, size_t size)
  16 This function adds a new smob type, named @var{name}, with instance size
  17 @var{size}, to the system.  The return value is a tag that is used in
  18 creating instances of the type.
  19
  20 If @var{size} is 0, the default @emph{free} function will do nothing.
  21
  22 If @var{size} is not 0, the default @emph{free} function will
  23 deallocate the memory block pointed to by @code{SCM_SMOB_DATA} with
  24 @code{scm_gc_free}.  The @var{WHAT} parameter in the call to
  25 @code{scm_gc_free} will be @var{NAME}.
  26
  27 Default values are provided for the @emph{mark}, @emph{free},
  28 @emph{print}, and @emph{equalp} functions, as described in
  29 @ref{Defining New Types (Smobs)}.  If you want to customize any of
  30 these functions, the call to @code{scm_make_smob_type} should be
  31 immediately followed by calls to one or several of
  32 @code{scm_set_smob_mark}, @code{scm_set_smob_free},
  33 @code{scm_set_smob_print}, and/or @code{scm_set_smob_equalp}.
  34 @end deftypefun
  35
  36 @deftypefn {C Function} void scm_set_smob_mark (scm_t_bits tc, SCM (*mark) (SCM obj))
  37 This function sets the smob marking procedure for the smob type specified by
  38 the tag @var{tc}. @var{tc} is the tag returned by @code{scm_make_smob_type}.
  39
  40 The @var{mark} procedure must cause @code{scm_gc_mark} to be called
  41 for every @code{SCM} value that is directly referenced by the smob
  42 instance @var{obj}.  One of these @code{SCM} values can be returned
  43 from the procedure and Guile will call @code{scm_gc_mark} for it.
  44 This can be used to avoid deep recursions for smob instances that form
  45 a list.
  46 @end deftypefn
  47
  48 @deftypefn {C Function} void scm_set_smob_free (scm_t_bits tc, size_t (*free) (SCM obj))
  49 This function sets the smob freeing procedure for the smob type
  50 specified by the tag @var{tc}. @var{tc} is the tag returned by
  51 @code{scm_make_smob_type}.
  52
  53 The @var{free} procedure must deallocate all resources that are
  54 directly associated with the smob instance @var{OBJ}.  It must assume
  55 that all @code{SCM} values that it references have already been freed
  56 and are thus invalid.
  57
  58 The @var{free} procedure must return 0.
  59 @end deftypefn
  60
  61 @deftypefn {C Function} void scm_set_smob_print (scm_t_bits tc, int (*print) (SCM obj, SCM port, scm_print_state* pstate))
  62 This function sets the smob printing procedure for the smob type
  63 specified by the tag @var{tc}. @var{tc} is the tag returned by
  64 @code{scm_make_smob_type}.
  65
  66 The @var{print} procedure should output a textual representation of
  67 the smob instance @var{obj} to @var{port}, using information in
  68 @var{pstate}.
  69
  70 The textual representation should be of the form @code{#<name ...>}.
  71 This ensures that @code{read} will not interpret it as some other
  72 Scheme value.
  73
  74 It is often best to ignore @var{pstate} and just print to @var{port}
  75 with @code{scm_display}, @code{scm_write}, @code{scm_simple_format},
  76 and @code{scm_puts}.
  77 @end deftypefn
  78
  79 @deftypefn {C Function} void scm_set_smob_equalp (scm_t_bits tc, SCM (*equalp) (SCM obj1, SCM obj1))
  80 This function sets the smob equality-testing predicate for the smob
  81 type specified by the tag @var{tc}. @var{tc} is the tag returned by
  82 @code{scm_make_smob_type}.
  83
  84 The @var{equalp} procedure should return @code{SCM_BOOL_T} when
  85 @var{obj1} is @code{equal?} to @var{obj2}.  Else it should return
  86 @var{SCM_BOOL_F}.  Both @var{obj1} and @var{obj2} are instances of the
  87 smob type @var{tc}.
  88 @end deftypefn
  89
  90 @deftypefn {C Function} void scm_assert_smob_type (scm_t_bits tag, SCM val)
  91 When @var{val} is a smob of the type indicated by @var{tag}, do nothing.
  92 Else, signal an error.
  93 @end deftypefn
  94
  95 @deftypefn {C Macro} int SCM_SMOB_PREDICATE (scm_t_bits tag, SCM exp)
  96 Return true iff @var{exp} is a smob instance of the type indicated by
  97 @var{tag}.  The expression @var{exp} can be evaluated more than once,
  98 so it shouldn't contain any side effects.
  99 @end deftypefn
 100
 101 @deftypefn {C Macro} void SCM_NEWSMOB (SCM value, scm_t_bits tag, void *data)
 102 @deftypefnx {C Macro} void SCM_NEWSMOB2 (SCM value, scm_t_bits tag, void *data, void *data2)
 103 @deftypefnx {C Macro} void SCM_NEWSMOB3 (SCM value, scm_t_bits tag, void *data, void *data2, void *data3)
 104 Make @var{value} contain a smob instance of the type with tag
 105 @var{tag} and smob data @var{data}, @var{data2}, and @var{data3}, as
 106 appropriate.
 107
 108 The @var{tag} is what has been returned by @code{scm_make_smob_type}.
 109 The initial values @var{data}, @var{data2}, and @var{data3} are of
 110 type @code{scm_t_bits}; when you want to use them for @code{SCM}
 111 values, these values need to be converted to a @code{scm_t_bits} first
 112 by using @code{SCM_UNPACK}.
 113
 114 The flags of the smob instance start out as zero.
 115 @end deftypefn
 116
 117 Since it is often the case (e.g., in smob constructors) that you will
 118 create a smob instance and return it, there is also a slightly specialized
 119 macro for this situation:
 120
 121 @deftypefn {C Macro} {} SCM_RETURN_NEWSMOB (scm_t_bits tag, void *data)
 122 @deftypefnx {C Macro} {} SCM_RETURN_NEWSMOB2 (scm_t_bits tag, void *data1, void *data2)
 123 @deftypefnx {C Macro} {} SCM_RETURN_NEWSMOB3 (scm_t_bits tag, void *data1, void *data2, void *data3)
 124 This macro expands to a block of code that creates a smob instance of
 125 the type with tag @var{tag} and smob data @var{data}, @var{data2}, and
 126 @var{data3}, as with @code{SCM_NEWSMOB}, etc., and causes the
 127 surrounding function to return that @code{SCM} value.  It should be
 128 the last piece of code in a block.
 129 @end deftypefn
 130
 131 @deftypefn {C Macro} scm_t_bits SCM_SMOB_FLAGS (SCM obj)
 132 Return the 16 extra bits of the smob @var{obj}.  No meaning is
 133 predefined for these bits, you can use them freely.
 134 @end deftypefn
 135
 136 @deftypefn {C Macro} scm_t_bits SCM_SET_SMOB_FLAGS (SCM obj, scm_t_bits flags)
 137 Set the 16 extra bits of the smob @var{obj} to @var{flags}.  No
 138 meaning is predefined for these bits, you can use them freely.
 139 @end deftypefn
 140
 141 @deftypefn {C Macro} scm_t_bits SCM_SMOB_DATA (SCM obj)
 142 @deftypefnx {C Macro} scm_t_bits SCM_SMOB_DATA_2 (SCM obj)
 143 @deftypefnx {C Macro} scm_t_bits SCM_SMOB_DATA_3 (SCM obj)
 144 Return the first (second, third) immediate word of the smob @var{obj}
 145 as a @code{scm_t_bits} value.  When the word contains a @code{SCM}
 146 value, use @code{SCM_SMOB_OBJECT} (etc.) instead.
 147 @end deftypefn
 148
 149 @deftypefn {C Macro} void SCM_SET_SMOB_DATA (SCM obj, scm_t_bits val)
 150 @deftypefnx {C Macro} void SCM_SET_SMOB_DATA_2 (SCM obj, scm_t_bits val)
 151 @deftypefnx {C Macro} void SCM_SET_SMOB_DATA_3 (SCM obj, scm_t_bits val)
 152 Set the first (second, third) immediate word of the smob @var{obj} to
 153 @var{val}.  When the word should be set to a @code{SCM} value, use
 154 @code{SCM_SMOB_SET_OBJECT} (etc.) instead.
 155 @end deftypefn
 156
 157 @deftypefn {C Macro} SCM SCM_SMOB_OBJECT (SCM obj)
 158 @deftypefnx {C Macro} SCM SCM_SMOB_OBJECT_2 (SCM obj)
 159 @deftypefnx {C Macro} SCM SCM_SMOB_OBJECT_3 (SCM obj)
 160 Return the first (second, third) immediate word of the smob @var{obj}
 161 as a @code{SCM} value.  When the word contains a @code{scm_t_bits}
 162 value, use @code{SCM_SMOB_DATA} (etc.) instead.
 163 @end deftypefn
 164
 165 @deftypefn {C Macro} void SCM_SET_SMOB_OBJECT (SCM obj, SCM val)
 166 @deftypefnx {C Macro} void SCM_SET_SMOB_OBJECT_2 (SCM obj, SCM val)
 167 @deftypefnx {C Macro} void SCM_SET_SMOB_OBJECT_3 (SCM obj, SCM val)
 168 Set the first (second, third) immediate word of the smob @var{obj} to
 169 @var{val}.  When the word should be set to a @code{scm_t_bits} value, use
 170 @code{SCM_SMOB_SET_DATA} (etc.) instead.
 171 @end deftypefn
 172
 173 @deftypefn {C Macro} {SCM *} SCM_SMOB_OBJECT_LOC (SCM obj)
 174 @deftypefnx {C Macro} {SCM *} SCM_SMOB_OBJECT_2_LOC (SCM obj)
 175 @deftypefnx {C Macro} {SCM *} SCM_SMOB_OBJECT_3_LOC (SCM obj)
 176 Return a pointer to the first (second, third) immediate word of the
 177 smob @var{obj}.  Note that this is a pointer to @code{SCM}.  If you
 178 need to work with @code{scm_t_bits} values, use @code{SCM_PACK} and
 179 @code{SCM_UNPACK}, as appropriate.
 180 @end deftypefn
 181
 182 @deftypefun SCM scm_markcdr (SCM @var{x})
 183 Mark the references in the smob @var{x}, assuming that @var{x}'s first
 184 data word contains an ordinary Scheme object, and @var{x} refers to no
 185 other objects.  This function simply returns @var{x}'s first data word.
 186 @end deftypefun
 187
 188 @c Local Variables:
 189 @c TeX-master: "guile.texi"
 190 @c End: