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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 API Overview |
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@section Overview of the Guile API |
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Guile's application programming interface (@dfn{API}) makes |
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functionality available that an application developer can use in either |
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C or Scheme programming. The interface consists of @dfn{elements} that |
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may be macros, functions or variables in C, and procedures, variables, |
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syntax or other types of object in Scheme. |
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Many elements are available to both Scheme and C, in a form that is |
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appropriate. For example, the @code{assq} Scheme procedure is also |
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available as @code{scm_assq} to C code. These elements are documented |
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only once, addressing both the Scheme and C aspects of them. |
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The Scheme name of an element is related to its C name in a regular |
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way. Also, a C function takes its parameters in a systematic way. |
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Normally, the name of a C function can be derived given its Scheme name, |
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using some simple textual transformations: |
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@itemize @bullet |
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@item |
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Replace @code{-} (hyphen) with @code{_} (underscore). |
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@item |
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Replace @code{?} (question mark) with @code{_p}. |
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@item |
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Replace @code{!} (exclamation point) with @code{_x}. |
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@item |
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Replace internal @code{->} with @code{_to_}. |
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@item |
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Replace @code{<=} (less than or equal) with @code{_leq}. |
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@item |
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Replace @code{>=} (greater than or equal) with @code{_geq}. |
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@item |
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Replace @code{<} (less than) with @code{_less}. |
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@item |
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Replace @code{>} (greater than) with @code{_gr}. |
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@item |
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Prefix with @code{scm_}. |
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@end itemize |
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@c Here is an Emacs Lisp command that prompts for a Scheme function name and |
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@c inserts the corresponding C function name into the buffer. |
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@c @example |
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@c (defun insert-scheme-to-C (name &optional use-gh) |
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@c "Transforms Scheme NAME, a string, to its C counterpart, and inserts it. |
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@c Prefix arg non-nil means use \"gh_\" prefix, otherwise use \"scm_\" prefix." |
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@c (interactive "sScheme name: \nP") |
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@c (let ((transforms '(("-" . "_") |
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@c ("?" . "_p") |
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@c ("!" . "_x") |
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@c ("->" . "_to_") |
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@c ("<=" . "_leq") |
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@c (">=" . "_geq") |
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@c ("<" . "_less") |
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@c (">" . "_gr") |
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@c ("@@" . "at")))) |
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@c (while transforms |
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@c (let ((trigger (concat "\\(.*\\)" |
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@c (regexp-quote (caar transforms)) |
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@c "\\(.*\\)")) |
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@c (sub (cdar transforms)) |
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@c (m nil)) |
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@c (while (setq m (string-match trigger name)) |
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@c (setq name (concat (match-string 1 name) |
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@c sub |
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@c (match-string 2 name))))) |
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@c (setq transforms (cdr transforms)))) |
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@c (insert (if use-gh "gh_" "scm_") name)) |
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@c @end example |
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A C function always takes a fixed number of arguments of type |
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@code{SCM}, even when the corresponding Scheme function takes a |
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variable number. |
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For some Scheme functions, some last arguments are optional; the |
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corresponding C function must always be invoked with all optional |
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arguments specified. To get the effect as if an argument has not been |
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specified, pass @code{SCM_UNDEFINED} as its value. You can not do |
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this for an argument in the middle; when one argument is |
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@code{SCM_UNDEFINED} all the ones following it must be |
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@code{SCM_UNDEFINED} as well. |
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Some Scheme functions take an arbitrary number of @emph{rest} |
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arguments; the corresponding C function must be invoked with a list of |
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all these arguments. This list is always the last argument of the C |
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function. |
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These two variants can also be combined. |
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The type of the return value of a C function that corresponds to a |
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Scheme function is always @code{SCM}. In the descriptions below, |
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types are therefore often omitted but for the return value and for the |
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arguments. |
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