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235 lines
10 KiB
Text
235 lines
10 KiB
Text
@c -*-texinfo-*-
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@c This is part of the GNU Guile Reference Manual.
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@c Copyright (C) 1996, 1997, 2000, 2001, 2002, 2003, 2004, 2009, 2013, 2014,
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@c 2016 Free Software Foundation, Inc.
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@c See the file guile.texi for copying conditions.
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@node Smobs
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@section Smobs
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@cindex smob
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This chapter contains reference information related to defining and
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working with smobs. @xref{Defining New Types (Smobs)}, for a
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tutorial-like introduction to smobs.
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@deftypefun scm_t_bits scm_make_smob_type (const char *name, size_t size)
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This function adds a new smob type, named @var{name}, with instance size
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@var{size}, to the system. The return value is a tag that is used in
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creating instances of the type.
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If @var{size} is 0, the default @emph{free} function will do nothing.
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If @var{size} is not 0, the default @emph{free} function will
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deallocate the memory block pointed to by @code{SCM_SMOB_DATA} with
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@code{scm_gc_free}. The @var{what} parameter in the call to
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@code{scm_gc_free} will be @var{name}.
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Default values are provided for the @emph{mark}, @emph{free},
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@emph{print}, and @emph{equalp} functions, as described in
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@ref{Defining New Types (Smobs)}. If you want to customize any of
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these functions, the call to @code{scm_make_smob_type} should be
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immediately followed by calls to one or several of
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@code{scm_set_smob_mark}, @code{scm_set_smob_free},
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@code{scm_set_smob_print}, and/or @code{scm_set_smob_equalp}.
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@end deftypefun
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@cindex finalizer
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@cindex finalization
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@deftypefn {C Function} void scm_set_smob_free (scm_t_bits tc, size_t (*free) (SCM obj))
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This function sets the smob freeing procedure (sometimes referred to as
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a @dfn{finalizer}) for the smob type specified by the tag
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@var{tc}. @var{tc} is the tag returned by @code{scm_make_smob_type}.
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The @var{free} procedure must deallocate all resources that are
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directly associated with the smob instance @var{obj}. It must assume
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that all @code{SCM} values that it references have already been freed
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and are thus invalid.
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It must also not call any libguile function or macro except
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@code{scm_gc_free}, @code{SCM_SMOB_FLAGS}, @code{SCM_SMOB_DATA},
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@code{SCM_SMOB_DATA_2}, and @code{SCM_SMOB_DATA_3}.
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The @var{free} procedure must return 0.
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Note that defining a freeing procedure is not necessary if the resources
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associated with @var{obj} consists only of memory allocated with
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@code{scm_gc_malloc} or @code{scm_gc_malloc_pointerless} because this
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memory is automatically reclaimed by the garbage collector when it is no
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longer needed (@pxref{Memory Blocks, @code{scm_gc_malloc}}).
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@end deftypefn
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Smob free functions must be thread-safe. @xref{Garbage Collecting
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Smobs}, for a discussion on finalizers and concurrency. If you are
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embedding Guile in an application that is not thread-safe, and you
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define smob types that need finalization, you might want to disable
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automatic finalization, and arrange to call
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@code{scm_run_finalizers} yourself.
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@deftypefn {C Function} int scm_set_automatic_finalization_enabled (int @var{enabled_p})
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Enable or disable automatic finalization. By default, Guile arranges to
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invoke object finalizers automatically, in a separate thread if
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possible. Passing a zero value for @var{enabled_p} will disable
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automatic finalization for Guile as a whole. If you disable automatic
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finalization, you will have to call @code{scm_run_finalizers}
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periodically.
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Unlike most other Guile functions, you can call
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@code{scm_set_automatic_finalization_enabled} before Guile has been
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initialized.
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Return the previous status of automatic finalization.
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@end deftypefn
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@deftypefn {C Function} int scm_run_finalizers (void)
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Invoke any pending finalizers. Return the number of finalizers that
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were invoked. This function should be called when automatic
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finalization is disabled, though it may be called if it is enabled as
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well.
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@end deftypefn
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@cindex precise marking
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@deftypefn {C Function} void scm_set_smob_mark (scm_t_bits tc, SCM (*mark) (SCM obj))
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This function sets the smob marking procedure for the smob type specified by
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the tag @var{tc}. @var{tc} is the tag returned by @code{scm_make_smob_type}.
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Defining a marking procedure may sometimes be unnecessary because large
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parts of the process' memory (with the exception of
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@code{scm_gc_malloc_pointerless} regions, and @code{malloc}- or
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@code{scm_malloc}-allocated memory) are scanned for live
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pointers@footnote{Conversely, in Guile up to the 1.8 series, the marking
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procedure was always required. The reason is that Guile's GC would only
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look for pointers in the memory area used for built-in types (the
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@dfn{cell heap}), not in user-allocated or statically allocated memory.
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This approach is often referred to as @dfn{precise marking}.}.
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The @var{mark} procedure must cause @code{scm_gc_mark} to be called
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for every @code{SCM} value that is directly referenced by the smob
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instance @var{obj}. One of these @code{SCM} values can be returned
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from the procedure and Guile will call @code{scm_gc_mark} for it.
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This can be used to avoid deep recursions for smob instances that form
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a list.
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It must not call any libguile function or macro except
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@code{scm_gc_mark}, @code{SCM_SMOB_FLAGS}, @code{SCM_SMOB_DATA},
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@code{SCM_SMOB_DATA_2}, and @code{SCM_SMOB_DATA_3}.
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@end deftypefn
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@deftypefn {C Function} void scm_set_smob_print (scm_t_bits tc, int (*print) (SCM obj, SCM port, scm_print_state* pstate))
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This function sets the smob printing procedure for the smob type
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specified by the tag @var{tc}. @var{tc} is the tag returned by
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@code{scm_make_smob_type}.
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The @var{print} procedure should output a textual representation of
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the smob instance @var{obj} to @var{port}, using information in
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@var{pstate}.
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The textual representation should be of the form @code{#<name ...>}.
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This ensures that @code{read} will not interpret it as some other
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Scheme value.
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It is often best to ignore @var{pstate} and just print to @var{port}
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with @code{scm_display}, @code{scm_write}, @code{scm_simple_format},
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and @code{scm_puts}.
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@end deftypefn
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@deftypefn {C Function} void scm_set_smob_equalp (scm_t_bits tc, SCM (*equalp) (SCM obj1, SCM obj2))
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This function sets the smob equality-testing predicate for the smob
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type specified by the tag @var{tc}. @var{tc} is the tag returned by
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@code{scm_make_smob_type}.
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The @var{equalp} procedure should return @code{SCM_BOOL_T} when
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@var{obj1} is @code{equal?} to @var{obj2}. Else it should return
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@code{SCM_BOOL_F}. Both @var{obj1} and @var{obj2} are instances of the
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smob type @var{tc}.
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@end deftypefn
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@deftypefn {C Function} void scm_assert_smob_type (scm_t_bits tag, SCM val)
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When @var{val} is a smob of the type indicated by @var{tag}, do nothing.
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Else, signal an error.
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@end deftypefn
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@deftypefn {C Macro} int SCM_SMOB_PREDICATE (scm_t_bits tag, SCM exp)
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Return true if @var{exp} is a smob instance of the type indicated by
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@var{tag}, or false otherwise. The expression @var{exp} can be
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evaluated more than once, so it shouldn't contain any side effects.
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@end deftypefn
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@deftypefn {C Function} SCM scm_new_smob (scm_t_bits tag, void *data)
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@deftypefnx {C Function} SCM scm_new_double_smob (scm_t_bits tag, void *data, void *data2, void *data3)
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Make a new smob of the type with tag @var{tag} and smob data @var{data},
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@var{data2}, and @var{data3}, as appropriate.
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The @var{tag} is what has been returned by @code{scm_make_smob_type}.
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The initial values @var{data}, @var{data2}, and @var{data3} are of
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type @code{scm_t_bits}; when you want to use them for @code{SCM}
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values, these values need to be converted to a @code{scm_t_bits} first
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by using @code{SCM_UNPACK}.
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The flags of the smob instance start out as zero.
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@end deftypefn
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@deftypefn {C Macro} scm_t_bits SCM_SMOB_FLAGS (SCM obj)
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Return the 16 extra bits of the smob @var{obj}. No meaning is
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predefined for these bits, you can use them freely.
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@end deftypefn
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@deftypefn {C Macro} scm_t_bits SCM_SET_SMOB_FLAGS (SCM obj, scm_t_bits flags)
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Set the 16 extra bits of the smob @var{obj} to @var{flags}. No
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meaning is predefined for these bits, you can use them freely.
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@end deftypefn
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@deftypefn {C Macro} scm_t_bits SCM_SMOB_DATA (SCM obj)
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@deftypefnx {C Macro} scm_t_bits SCM_SMOB_DATA_2 (SCM obj)
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@deftypefnx {C Macro} scm_t_bits SCM_SMOB_DATA_3 (SCM obj)
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Return the first (second, third) immediate word of the smob @var{obj}
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as a @code{scm_t_bits} value. When the word contains a @code{SCM}
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value, use @code{SCM_SMOB_OBJECT} (etc.) instead.
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@end deftypefn
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@deftypefn {C Macro} void SCM_SET_SMOB_DATA (SCM obj, scm_t_bits val)
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@deftypefnx {C Macro} void SCM_SET_SMOB_DATA_2 (SCM obj, scm_t_bits val)
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@deftypefnx {C Macro} void SCM_SET_SMOB_DATA_3 (SCM obj, scm_t_bits val)
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Set the first (second, third) immediate word of the smob @var{obj} to
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@var{val}. When the word should be set to a @code{SCM} value, use
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@code{SCM_SMOB_SET_OBJECT} (etc.) instead.
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@end deftypefn
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@deftypefn {C Macro} SCM SCM_SMOB_OBJECT (SCM obj)
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@deftypefnx {C Macro} SCM SCM_SMOB_OBJECT_2 (SCM obj)
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@deftypefnx {C Macro} SCM SCM_SMOB_OBJECT_3 (SCM obj)
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Return the first (second, third) immediate word of the smob @var{obj}
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as a @code{SCM} value. When the word contains a @code{scm_t_bits}
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value, use @code{SCM_SMOB_DATA} (etc.) instead.
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@end deftypefn
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@deftypefn {C Macro} void SCM_SET_SMOB_OBJECT (SCM obj, SCM val)
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@deftypefnx {C Macro} void SCM_SET_SMOB_OBJECT_2 (SCM obj, SCM val)
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@deftypefnx {C Macro} void SCM_SET_SMOB_OBJECT_3 (SCM obj, SCM val)
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Set the first (second, third) immediate word of the smob @var{obj} to
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@var{val}. When the word should be set to a @code{scm_t_bits} value, use
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@code{SCM_SMOB_SET_DATA} (etc.) instead.
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@end deftypefn
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@deftypefn {C Macro} {SCM *} SCM_SMOB_OBJECT_LOC (SCM obj)
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@deftypefnx {C Macro} {SCM *} SCM_SMOB_OBJECT_2_LOC (SCM obj)
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@deftypefnx {C Macro} {SCM *} SCM_SMOB_OBJECT_3_LOC (SCM obj)
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Return a pointer to the first (second, third) immediate word of the
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smob @var{obj}. Note that this is a pointer to @code{SCM}. If you
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need to work with @code{scm_t_bits} values, use @code{SCM_PACK} and
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@code{SCM_UNPACK}, as appropriate.
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@end deftypefn
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@deftypefun SCM scm_markcdr (SCM @var{x})
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Mark the references in the smob @var{x}, assuming that @var{x}'s first
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data word contains an ordinary Scheme object, and @var{x} refers to no
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other objects. This function simply returns @var{x}'s first data word.
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@end deftypefun
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@c Local Variables:
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@c TeX-master: "guile.texi"
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@c End:
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