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@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 |
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@c Free Software Foundation, Inc. |
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@c See the file guile.texi for copying conditions. |
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@node The SCM Type |
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@section The SCM Type |
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Guile represents all Scheme values with the single C type @code{SCM}. |
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For an introduction to this topic, @xref{Dynamic Types}. |
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@deftp {C Type} SCM |
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@code{SCM} is the user level abstract C type that is used to represent |
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all of Guile's Scheme objects, no matter what the Scheme object type is. |
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No C operation except assignment is guaranteed to work with variables of |
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type @code{SCM}, so you should only use macros and functions to work |
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with @code{SCM} values. Values are converted between C data types and |
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the @code{SCM} type with utility functions and macros. |
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@end deftp |
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@cindex SCM data type |
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@deftp {C Type} scm_t_bits |
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@code{scm_t_bits} is an unsigned integral data type that is guaranteed |
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to be large enough to hold all information that is required to |
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represent any Scheme object. While this data type is mostly used to |
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implement Guile's internals, the use of this type is also necessary to |
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write certain kinds of extensions to Guile. |
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@end deftp |
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@deftp {C Type} scm_t_signed_bits |
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This is a signed integral type of the same size as @code{scm_t_bits}. |
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@end deftp |
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@deftypefn {C Macro} scm_t_bits SCM_UNPACK (SCM @var{x}) |
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Transforms the @code{SCM} value @var{x} into its representation as an |
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integral type. Only after applying @code{SCM_UNPACK} it is possible to |
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access the bits and contents of the @code{SCM} value. |
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@end deftypefn |
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@deftypefn {C Macro} SCM SCM_PACK (scm_t_bits @var{x}) |
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Takes a valid integral representation of a Scheme object and transforms |
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it into its representation as a @code{SCM} value. |
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@end deftypefn |
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