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 It must also not call any libguile function or macro except
  59 @code{scm_gc_free}, @code{SCM_SMOB_FLAGS}, @code{SCM_SMOB_DATA},
  60 @code{SCM_SMOB_DATA_2}, and @code{SCM_SMOB_DATA_3}.
  61
  62 The @var{free} procedure must return 0.
  63 @end deftypefn
  64
  65 @deftypefn {C Function} void scm_set_smob_print (scm_t_bits tc, int (*print) (SCM obj, SCM port, scm_print_state* pstate))
  66 This function sets the smob printing procedure for the smob type
  67 specified by the tag @var{tc}. @var{tc} is the tag returned by
  68 @code{scm_make_smob_type}.
  69
  70 The @var{print} procedure should output a textual representation of
  71 the smob instance @var{obj} to @var{port}, using information in
  72 @var{pstate}.
  73
  74 The textual representation should be of the form @code{#<name ...>}.
  75 This ensures that @code{read} will not interpret it as some other
  76 Scheme value.
  77
  78 It is often best to ignore @var{pstate} and just print to @var{port}
  79 with @code{scm_display}, @code{scm_write}, @code{scm_simple_format},
  80 and @code{scm_puts}.
  81 @end deftypefn
  82
  83 @deftypefn {C Function} void scm_set_smob_equalp (scm_t_bits tc, SCM (*equalp) (SCM obj1, SCM obj1))
  84 This function sets the smob equality-testing predicate for the smob
  85 type specified by the tag @var{tc}. @var{tc} is the tag returned by
  86 @code{scm_make_smob_type}.
  87
  88 The @var{equalp} procedure should return @code{SCM_BOOL_T} when
  89 @var{obj1} is @code{equal?} to @var{obj2}.  Else it should return
  90 @var{SCM_BOOL_F}.  Both @var{obj1} and @var{obj2} are instances of the
  91 smob type @var{tc}.
  92 @end deftypefn
  93
  94 @deftypefn {C Function} void scm_assert_smob_type (scm_t_bits tag, SCM val)
  95 When @var{val} is a smob of the type indicated by @var{tag}, do nothing.
  96 Else, signal an error.
  97 @end deftypefn
  98
  99 @deftypefn {C Macro} int SCM_SMOB_PREDICATE (scm_t_bits tag, SCM exp)
 100 Return true iff @var{exp} is a smob instance of the type indicated by
 101 @var{tag}.  The expression @var{exp} can be evaluated more than once,
 102 so it shouldn't contain any side effects.
 103 @end deftypefn
 104
 105 @deftypefn {C Macro} void SCM_NEWSMOB (SCM value, scm_t_bits tag, void *data)
 106 @deftypefnx {C Macro} void SCM_NEWSMOB2 (SCM value, scm_t_bits tag, void *data, void *data2)
 107 @deftypefnx {C Macro} void SCM_NEWSMOB3 (SCM value, scm_t_bits tag, void *data, void *data2, void *data3)
 108 Make @var{value} contain a smob instance of the type with tag
 109 @var{tag} and smob data @var{data}, @var{data2}, and @var{data3}, as
 110 appropriate.
 111
 112 The @var{tag} is what has been returned by @code{scm_make_smob_type}.
 113 The initial values @var{data}, @var{data2}, and @var{data3} are of
 114 type @code{scm_t_bits}; when you want to use them for @code{SCM}
 115 values, these values need to be converted to a @code{scm_t_bits} first
 116 by using @code{SCM_UNPACK}.
 117
 118 The flags of the smob instance start out as zero.
 119 @end deftypefn
 120
 121 Since it is often the case (e.g., in smob constructors) that you will
 122 create a smob instance and return it, there is also a slightly specialized
 123 macro for this situation:
 124
 125 @deftypefn {C Macro} {} SCM_RETURN_NEWSMOB (scm_t_bits tag, void *data)
 126 @deftypefnx {C Macro} {} SCM_RETURN_NEWSMOB2 (scm_t_bits tag, void *data1, void *data2)
 127 @deftypefnx {C Macro} {} SCM_RETURN_NEWSMOB3 (scm_t_bits tag, void *data1, void *data2, void *data3)
 128 This macro expands to a block of code that creates a smob instance of
 129 the type with tag @var{tag} and smob data @var{data}, @var{data2}, and
 130 @var{data3}, as with @code{SCM_NEWSMOB}, etc., and causes the
 131 surrounding function to return that @code{SCM} value.  It should be
 132 the last piece of code in a block.
 133 @end deftypefn
 134
 135 @deftypefn {C Macro} scm_t_bits SCM_SMOB_FLAGS (SCM obj)
 136 Return the 16 extra bits of the smob @var{obj}.  No meaning is
 137 predefined for these bits, you can use them freely.
 138 @end deftypefn
 139
 140 @deftypefn {C Macro} scm_t_bits SCM_SET_SMOB_FLAGS (SCM obj, scm_t_bits flags)
 141 Set the 16 extra bits of the smob @var{obj} to @var{flags}.  No
 142 meaning is predefined for these bits, you can use them freely.
 143 @end deftypefn
 144
 145 @deftypefn {C Macro} scm_t_bits SCM_SMOB_DATA (SCM obj)
 146 @deftypefnx {C Macro} scm_t_bits SCM_SMOB_DATA_2 (SCM obj)
 147 @deftypefnx {C Macro} scm_t_bits SCM_SMOB_DATA_3 (SCM obj)
 148 Return the first (second, third) immediate word of the smob @var{obj}
 149 as a @code{scm_t_bits} value.  When the word contains a @code{SCM}
 150 value, use @code{SCM_SMOB_OBJECT} (etc.) instead.
 151 @end deftypefn
 152
 153 @deftypefn {C Macro} void SCM_SET_SMOB_DATA (SCM obj, scm_t_bits val)
 154 @deftypefnx {C Macro} void SCM_SET_SMOB_DATA_2 (SCM obj, scm_t_bits val)
 155 @deftypefnx {C Macro} void SCM_SET_SMOB_DATA_3 (SCM obj, scm_t_bits val)
 156 Set the first (second, third) immediate word of the smob @var{obj} to
 157 @var{val}.  When the word should be set to a @code{SCM} value, use
 158 @code{SCM_SMOB_SET_OBJECT} (etc.) instead.
 159 @end deftypefn
 160
 161 @deftypefn {C Macro} SCM SCM_SMOB_OBJECT (SCM obj)
 162 @deftypefnx {C Macro} SCM SCM_SMOB_OBJECT_2 (SCM obj)
 163 @deftypefnx {C Macro} SCM SCM_SMOB_OBJECT_3 (SCM obj)
 164 Return the first (second, third) immediate word of the smob @var{obj}
 165 as a @code{SCM} value.  When the word contains a @code{scm_t_bits}
 166 value, use @code{SCM_SMOB_DATA} (etc.) instead.
 167 @end deftypefn
 168
 169 @deftypefn {C Macro} void SCM_SET_SMOB_OBJECT (SCM obj, SCM val)
 170 @deftypefnx {C Macro} void SCM_SET_SMOB_OBJECT_2 (SCM obj, SCM val)
 171 @deftypefnx {C Macro} void SCM_SET_SMOB_OBJECT_3 (SCM obj, SCM val)
 172 Set the first (second, third) immediate word of the smob @var{obj} to
 173 @var{val}.  When the word should be set to a @code{scm_t_bits} value, use
 174 @code{SCM_SMOB_SET_DATA} (etc.) instead.
 175 @end deftypefn
 176
 177 @deftypefn {C Macro} {SCM *} SCM_SMOB_OBJECT_LOC (SCM obj)
 178 @deftypefnx {C Macro} {SCM *} SCM_SMOB_OBJECT_2_LOC (SCM obj)
 179 @deftypefnx {C Macro} {SCM *} SCM_SMOB_OBJECT_3_LOC (SCM obj)
 180 Return a pointer to the first (second, third) immediate word of the
 181 smob @var{obj}.  Note that this is a pointer to @code{SCM}.  If you
 182 need to work with @code{scm_t_bits} values, use @code{SCM_PACK} and
 183 @code{SCM_UNPACK}, as appropriate.
 184 @end deftypefn
 185
 186 @deftypefun SCM scm_markcdr (SCM @var{x})
 187 Mark the references in the smob @var{x}, assuming that @var{x}'s first
 188 data word contains an ordinary Scheme object, and @var{x} refers to no
 189 other objects.  This function simply returns @var{x}'s first data word.
 190 @end deftypefun
 191
 192 @c Local Variables:
 193 @c TeX-master: "guile.texi"
 194 @c End: