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@page
@node API Overview
@chapter Overview of the Guile API
Guile's application programming interface (@dfn{API}) makes
functionality available that an application developer can use in either
C or Scheme programming. The interface consists of @dfn{elements} that
may be macros, functions or variables in C, and procedures, variables,
syntax or other types of object in Scheme. Broadly speaking, the
interface as a whole can be divided into three groups.
@enumerate
@item
Elements that are available equivalently as C functions or Scheme
procedures.
@item
Elements that are only available as macros, functions or variables for C
programming.
@item
Elements that are only available as procedures or other objects in
Scheme.
@end enumerate
Functions/procedures in the first group are often known as
@dfn{primitives}, @dfn{subrs} or @dfn{builtins}. An example is the
@code{assq} Scheme procedure, which is also available as @code{scm_assq}
in C.
Elements in the second and third groups exist because they provide
additional language-specific benefits in either Scheme or C. Examples
are the C macro @code{SCM_CONSP}, which is faster and more convenient in
C programming than the primitive @code{scm_pair_p}, and the
procedure-with-setter @code{make-object-property}, which provides a
more convenient property handling interface in Scheme than the
primitives on which it is based.
@menu
* Primitives:: Identical function for Scheme and C.
* C Only:: Elements only available in C.
* Scheme Only:: Elements only available in Scheme.
* Reference Layout:: The layout of this part of the manual.
@end menu
@node Primitives
@section Identical Function in both Scheme and C
They form the majority of the API, and allow both C and Scheme
programmers to perform identical operations.
@c @node Scheme Primitives
@c @chapter Writing Scheme primitives in C
@c - according to the menu in guile.texi - NJ 2001/1/26
@c @chapter Relationship between Scheme and C functions
@c Chapter contents contributed by Thien-Thi Nguyen <ttn@gnu.org>.
Scheme procedures marked "primitive functions" have a regular interface
when calling from C, reflected in two areas: the name of a C function, and
the convention for passing non-required arguments to this function.
@c Although the vast majority of functions support these relationships,
@c there are some exceptions.
@menu
* Transforming Scheme name to C name::
* Structuring argument lists for C functions::
@c * Exceptions to the regularity::
@end menu
@node Transforming Scheme name to C name
@subsection Transforming Scheme name to C name
Normally, the name of a C function can be derived given its Scheme name,
using some simple textual transformations:
@itemize @bullet
@item
Replace @code{-} (hyphen) with @code{_} (underscore).
@item
Replace @code{?} (question mark) with "_p".
@item
Replace @code{!} (exclamation point) with "_x".
@item
Replace internal @code{->} with "_to_".
@item
Replace @code{<=} (less than or equal) with "_leq".
@item
Replace @code{>=} (greater than or equal) with "_geq".
@item
Replace @code{<} (less than) with "_less".
@item
Replace @code{>} (greater than) with "_gr".
@item
Replace @code{@@} with "at". [Omit?]
@item
Prefix with "gh_" (or "scm_" if you are ignoring the gh interface).
@item
[Anything else? --ttn, 2000/01/16 15:17:28]
@end itemize
Here is an Emacs Lisp command that prompts for a Scheme function name and
inserts the corresponding C function name into the buffer.
@example
(defun insert-scheme-to-C (name &optional use-gh)
"Transforms Scheme NAME, a string, to its C counterpart, and inserts it.
Prefix arg non-nil means use \"gh_\" prefix, otherwise use \"scm_\" prefix."
(interactive "sScheme name: \nP")
(let ((transforms '(("-" . "_")
("?" . "_p")
("!" . "_x")
("->" . "_to_")
("<=" . "_leq")
(">=" . "_geq")
("<" . "_less")
(">" . "_gr")
("@@" . "at"))))
(while transforms
(let ((trigger (concat "\\(.*\\)"
(regexp-quote (caar transforms))
"\\(.*\\)"))
(sub (cdar transforms))
(m nil))
(while (setq m (string-match trigger name))
(setq name (concat (match-string 1 name)
sub
(match-string 2 name)))))
(setq transforms (cdr transforms))))
(insert (if use-gh "gh_" "scm_") name))
@end example
@node Structuring argument lists for C functions
@subsection Structuring argument lists for C functions
The C function's arguments will be all of the Scheme procedure's
arguments, both required and optional; if the Scheme procedure takes a
``rest'' argument, that will be a final argument to the C function. The
C function's arguments, as well as its return type, will be @code{SCM}.
@node C Only
@section Elements Available Only in C
For C this is usually a matter of better performance (e.g. the
@code{SCM_CONSP} macro) or of accepting C language types rather than the
generic @code{SCM}.
@node Scheme Only
@section Elements Available Only in Scheme
@node Reference Layout
@section Reference Material Layout
This part of the reference manual documents all of Guile's core
Scheme-level language and features in functionally-related groups.
Where a particular section of the manual includes both R5RS-compliant
parts and Guile-specific extensions, the text indicates which parts of
the documentation describe R5RS behaviour and which parts describe Guile
extensions.
For a quick way of identifying the parts of Guile that implement
R5RS-compliant features, see the R5RS index: @ref{R5RS Index}.
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