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110 lines
3.2 KiB
Text
110 lines
3.2 KiB
Text
@page
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@node Scheme Primitives
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@c @chapter Writing Scheme primitives in C
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@c - according to the menu in guile.texi - NJ 2001/1/26
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@chapter Relationship between Scheme and C functions
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Scheme procedures marked "primitive functions" have a regular interface
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when calling from C, reflected in two areas: the name of a C function, and
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the convention for passing non-required arguments to this function.
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@c Although the vast majority of functions support these relationships,
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@c there are some exceptions.
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@menu
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* Transforming Scheme name to C name::
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* Structuring argument lists for C functions::
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@c * Exceptions to the regularity::
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@end menu
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@node Transforming Scheme name to C name
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@section Transforming Scheme name to C name
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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 "_p".
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@item
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Replace @code{!} (exclamation point) with "_x".
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@item
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Replace internal @code{->} with "_to_".
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@item
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Replace @code{<=} (less than or equal) with "_leq".
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@item
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Replace @code{>=} (greater than or equal) with "_geq".
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@item
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Replace @code{<} (less than) with "_less".
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@item
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Replace @code{>} (greater than) with "_gr".
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@item
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Replace @code{@@} with "at". [Omit?]
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@item
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Prefix with "gh_" (or "scm_" if you are ignoring the gh interface).
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@item
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[Anything else? --ttn, 2000/01/16 15:17:28]
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@end itemize
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Here is an Emacs Lisp command that prompts for a Scheme function name and
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inserts the corresponding C function name into the buffer.
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@example
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(defun insert-scheme-to-C (name &optional use-gh)
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"Transforms Scheme NAME, a string, to its C counterpart, and inserts it.
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Prefix arg non-nil means use \"gh_\" prefix, otherwise use \"scm_\" prefix."
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(interactive "sScheme name: \nP")
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(let ((transforms '(("-" . "_")
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("?" . "_p")
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("!" . "_x")
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("->" . "_to_")
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("<=" . "_leq")
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(">=" . "_geq")
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("<" . "_less")
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(">" . "_gr")
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("@@" . "at"))))
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(while transforms
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(let ((trigger (concat "\\(.*\\)"
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(regexp-quote (caar transforms))
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"\\(.*\\)"))
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(sub (cdar transforms))
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(m nil))
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(while (setq m (string-match trigger name))
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(setq name (concat (match-string 1 name)
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sub
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(match-string 2 name)))))
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(setq transforms (cdr transforms))))
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(insert (if use-gh "gh_" "scm_") name))
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@end example
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@node Structuring argument lists for C functions
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@section Structuring argument lists for C functions
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The C function's arguments will be all of the Scheme procedure's
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arguments, both required and optional; if the Scheme procedure takes a
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``rest'' argument, that will be a final argument to the C function. The
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C function's arguments, as well as its return type, will be @code{SCM}.
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@c @node Exceptions to the regularity
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@c @section Exceptions to the regularity
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@c
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@c There are some exceptions to the regular structure described above.
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@c scm.texi ends here
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