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-@page
-@node GH
-@chapter GH: A Portable C to Scheme Interface
-@cindex libguile - gh
-@cindex gh
-@cindex gh - reference manual
-
-This chapter shows how to use the GH interface to call Guile from your
-application's C code, and to add new Scheme level procedures to Guile
-whose behaviour is specified by application specific code written in C.
-
-Note, however, that the GH interface is now deprecated, and developers
-are encouraged to switch to using the scm interface instead. Therefore,
-for each GH feature, this chapter should also document how to achieve
-the same result using the scm interface.
-
-@menu
-* GH deprecation:: Why the GH interface is now deprecated.
-* gh preliminaries::
-* Data types and constants defined by gh::
-* Starting and controlling the interpreter::
-* Error messages::
-* Executing Scheme code::
-* Defining new Scheme procedures in C::
-* Converting data between C and Scheme::
-* Type predicates::
-* Equality predicates::
-* Memory allocation and garbage collection::
-* Calling Scheme procedures from C::
-* Mixing gh and scm APIs::
-* scm transition summary::
-@end menu
-
-
-@node GH deprecation
-@section Why the GH Interface is Now Deprecated
-
-Historically, the GH interface was the product of a practical problem
-and a neat idea. The practical problem was that the interface of the
-@code{scm_} functions with which Guile itself was written (inherited
-from Aubrey Jaffer's SCM) was so closely tied to the (rather arcane)
-details of the internal data representation that it was extremely
-difficult to write a Guile extension using these functions. The neat
-idea was to define a high level language extension interface in such a
-way that other extension language projects, not just Guile, would be
-able to provide an implementation of that interface; then applications
-using this interface could be compiled with whichever of the various
-available implementations they chose. So the GH interface was created,
-and advertised both as the recommended interface for application
-developers wishing to use Guile, and as a portable high level interface
-that could theoretically be implemented by other extension language
-projects.
-
-Time passed, and various things changed. Crucially, an enormous number
-of improvements were made to the @code{scm_} interface that Guile itself
-uses in its implementation, with the result that it is now both easy and
-comfortable to write a Guile extension with this interface. At the same
-time, the contents of the GH interface were somewhat neglected by the
-core Guile developers, such that some key operations --- such as smob
-creation and management --- are simply not possible using GH alone.
-Finally, the idea of multiple implementations of the GH interface did
-not really crystallize (apart, I believe, from a short lived
-implementation by the MzScheme project).
-
-For all these reasons, the Guile developers have decided to deprecate
-the GH interface --- which means that support for GH will be completely
-removed after the next few releases --- and to focus only on the
-@code{scm_} interface, with additions to ensure that it is as easy to
-use in all respects as GH was.
-
-It remains an open question whether a deep kind of interface portability
-would be useful for extension language-based applications, and it may
-still be an interesting project to attempt to define a corresponding
-GH-like interface, but the Guile developers no longer plan to try to do
-this as part of the core Guile project.
-
-
-@node gh preliminaries
-@section gh preliminaries
-
-To use gh, you must have the following toward the beginning of your C
-source:
-@smallexample
-#include <guile/gh.h>
-@end smallexample
-@cindex gh - headers
-
-When you link, you will have to add at least @code{-lguile} to the list
-of libraries. If you are using more of Guile than the basic Scheme
-interpreter, you will have to add more libraries.
-@cindex gh - linking
-
-
-@node Data types and constants defined by gh
-@section Data types and constants defined by gh
-@cindex libguile - data types
-
-The following C constants and data types are defined in gh:
-
-@deftp {Data type} SCM
-This is a C data type used to store all Scheme data, no matter what the
-Scheme type. Values are converted between C data types and the SCM type
-with utility functions described below (@pxref{Converting data between C
-and Scheme}). [FIXME: put in references to Jim's essay and so forth.]
-@end deftp
-@cindex SCM data type
-
-@defvr Constant SCM_BOOL_T
-@defvrx Constant SCM_BOOL_F
-The @emph{Scheme} values returned by many boolean procedures in
-libguile.
-
-This can cause confusion because they are different from 0 and 1. In
-testing a boolean function in libguile programming, you must always make
-sure that you check the spec: @code{gh_} and @code{scm_} functions will
-usually return @code{SCM_BOOL_T} and @code{SCM_BOOL_F}, but other C
-functions usually can be tested against 0 and 1, so programmers' fingers
-tend to just type @code{if (boolean_function()) @{ ... @}}
-@end defvr
-
-@defvr Constant SCM_UNSPECIFIED
-This is a SCM value that is not the same as any legal Scheme value. It
-is the value that a Scheme function returns when its specification says
-that its return value is unspecified.
-@end defvr
-
-@defvr Constant SCM_UNDEFINED
-This is another SCM value that is not the same as any legal Scheme
-value. It is the value used to mark variables that do not yet have a
-value, and it is also used in C to terminate functions with variable
-numbers of arguments, such as @code{gh_list()}.
-@end defvr
-
-
-@node Starting and controlling the interpreter
-@section Starting and controlling the interpreter
-@cindex libguile - start interpreter
-
-In almost every case, your first @code{gh_} call will be:
-
-@deftypefun void gh_enter (int @var{argc}, char *@var{argv}[], void (*@var{main_prog})())
-Starts up a Scheme interpreter with all the builtin Scheme primitives.
-@code{gh_enter()} never exits, and the user's code should all be in the
-@code{@var{main_prog}()} function. @code{argc} and @code{argv} will be
-passed to @var{main_prog}.
-
-@deftypefun void main_prog (int @var{argc}, char *@var{argv}[])
-This is the user's main program. It will be invoked by
-@code{gh_enter()} after Guile has been started up.
-@end deftypefun
-
-Note that you can use @code{gh_repl} inside @code{gh_enter} (in other
-words, inside the code for @code{main-prog}) if you want the program to
-be controlled by a Scheme read-eval-print loop.
-@end deftypefun
-
-@cindex read eval print loop -- from the gh_ interface
-@cindex REPL -- from the gh_ interface
-A convenience routine which enters the Guile interpreter with the
-standard Guile read-eval-print loop (@dfn{REPL}) is:
-
-@deftypefun void gh_repl (int @var{argc}, char *@var{argv}[])
-Enters the Scheme interpreter giving control to the Scheme REPL.
-Arguments are processed as if the Guile program @file{guile} were being
-invoked.
-
-Note that @code{gh_repl} should be used @emph{inside} @code{gh_enter},
-since any Guile interpreter calls are meaningless unless they happen in
-the context of the interpreter.
-
-Also note that when you use @code{gh_repl}, your program will be
-controlled by Guile's REPL (which is written in Scheme and has many
-useful features). Use straight C code inside @code{gh_enter} if you
-want to maintain execution control in your C program.
-@end deftypefun
-
-You will typically use @code{gh_enter} and @code{gh_repl} when you
-want a Guile interpreter enhanced by your own libraries, but otherwise
-quite normal. For example, to build a Guile--derived program that
-includes some random number routines @dfn{GSL} (GNU Scientific Library),
-you would write a C program that looks like this:
-
-@smallexample
-#include <guile/gh.h>
-#include <gsl_ran.h>
-
-/* random number suite */
-SCM gw_ran_seed(SCM s)
-@{
- gsl_ran_seed(gh_scm2int(s));
- return SCM_UNSPECIFIED;
-@}
-
-SCM gw_ran_random()
-@{
- SCM x;
-
- x = gh_ulong2scm(gsl_ran_random());
- return x;
-@}
-
-SCM gw_ran_uniform()
-@{
- SCM x;
-
- x = gh_double2scm(gsl_ran_uniform());
- return x;
-@}
-SCM gw_ran_max()
-@{
- return gh_double2scm(gsl_ran_max());
-@}
-
-void
-init_gsl()
-@{
- /* random number suite */
- gh_new_procedure("gsl-ran-seed", gw_ran_seed, 1, 0, 0);
- gh_new_procedure("gsl-ran-random", gw_ran_random, 0, 0, 0);
- gh_new_procedure("gsl-ran-uniform", gw_ran_uniform, 0, 0, 0);
- gh_new_procedure("gsl-ran-max", gw_ran_max, 0, 0, 0);
-@}
-
-void
-main_prog (int argc, char *argv[])
-@{
- init_gsl();
-
- gh_repl(argc, argv);
-@}
-
-int
-main (int argc, char *argv[])
-@{
- gh_enter (argc, argv, main_prog);
-@}
-@end smallexample
-
-Then, supposing the C program is in @file{guile-gsl.c}, you could
-compile it with @kbd{gcc -o guile-gsl guile-gsl.c -lguile -lgsl}.
-
-The resulting program @file{guile-gsl} would have new primitive
-procedures @code{gsl-ran-random}, @code{gsl-ran-gaussian} and so forth.
-
-
-@node Error messages
-@section Error messages
-@cindex libguile - error messages
-@cindex error messages in libguile
-
-[FIXME: need to fill this based on Jim's new mechanism]
-
-
-@node Executing Scheme code
-@section Executing Scheme code
-@cindex libguile - executing Scheme
-@cindex executing Scheme
-
-Once you have an interpreter running, you can ask it to evaluate Scheme
-code. There are two calls that implement this:
-
-@deftypefun SCM gh_eval_str (char *@var{scheme_code})
-This asks the interpreter to evaluate a single string of Scheme code,
-and returns the result of the last expression evaluated.
-
-Note that the line of code in @var{scheme_code} must be a well formed
-Scheme expression. If you have many lines of code before you balance
-parentheses, you must either concatenate them into one string, or use
-@code{gh_eval_file()}.
-@end deftypefun
-
-@deftypefun SCM gh_eval_file (char *@var{fname})
-@deftypefunx SCM gh_load (char *@var{fname})
-@code{gh_eval_file} is completely analogous to @code{gh_eval_str()},
-except that a whole file is evaluated instead of a string.
-@code{gh_eval_file} returns @code{SCM_UNSPECIFIED}.
-
-@code{gh_load} is identical to @code{gh_eval_file} (it's a macro that
-calls @code{gh_eval_file} on its argument). It is provided to start
-making the @code{gh_} interface match the R5RS Scheme procedures
-closely.
-@end deftypefun
-
-
-@node Defining new Scheme procedures in C
-@section Defining new Scheme procedures in C
-@cindex libguile - new procedures
-@cindex new procedures
-@cindex procedures, new
-@cindex new primitives
-@cindex primitives, new
-
-The real interface between C and Scheme comes when you can write new
-Scheme procedures in C. This is done through the routine
-
-
-@deftypefn {Libguile high} SCM gh_new_procedure (char *@var{proc_name}, SCM (*@var{fn})(), int @var{n_required_args}, int @var{n_optional_args}, int @var{restp})
-@code{gh_new_procedure} defines a new Scheme procedure. Its Scheme name
-will be @var{proc_name}, it will be implemented by the C function
-(*@var{fn})(), it will take at least @var{n_required_args} arguments,
-and at most @var{n_optional_args} extra arguments.
-
-When the @var{restp} parameter is 1, the procedure takes a final
-argument: a list of remaining parameters.
-
-@code{gh_new_procedure} returns an SCM value representing the procedure.
-
-The C function @var{fn} should have the form
-@deftypefn {Libguile high} SCM fn (SCM @var{req1}, SCM @var{req2}, ..., SCM @var{opt1}, SCM @var{opt2}, ..., SCM @var{rest_args})
-The arguments are all passed as SCM values, so the user will have to use
-the conversion functions to convert to standard C types.
-
-Examples of C functions used as new Scheme primitives can be found in
-the sample programs @code{learn0} and @code{learn1}.
-@end deftypefn
-
-@end deftypefn
-
-@strong{Rationale:} this is the correct way to define new Scheme
-procedures in C. The ugly mess of arguments is required because of how
-C handles procedures with variable numbers of arguments.
-
-@strong{Note:} what about documentation strings?
-
-@cartouche
-There are several important considerations to be made when writing the C
-routine @code{(*fn)()}.
-
-First of all the C routine has to return type @code{SCM}.
-
-Second, all arguments passed to the C function will be of type
-@code{SCM}.
-
-Third: the C routine is now subject to Scheme flow control, which means
-that it could be interrupted at any point, and then reentered. This
-means that you have to be very careful with operations such as
-allocating memory, modifying static data @dots{}
-
-Fourth: to get around the latter issue, you can use
-@code{GH_DEFER_INTS} and @code{GH_ALLOW_INTS}.
-@end cartouche
-
-@defmac GH_DEFER_INTS
-@defmacx GH_ALLOW_INTS
-These macros disable and re-enable Scheme's flow control. They
-@end defmac
-
-
-@c [??? have to do this right; maybe using subsections, or maybe creating a
-@c section called Flow control issues...]
-
-@c [??? Go into exhaustive detail with examples of the various possible
-@c combinations of required and optional args...]
-
-
-@node Converting data between C and Scheme
-@section Converting data between C and Scheme
-@cindex libguile - converting data
-@cindex data conversion
-@cindex converting data
-
-Guile provides mechanisms to convert data between C and Scheme. This
-allows new builtin procedures to understand their arguments (which are
-of type @code{SCM}) and return values of type @code{SCM}.
-
-
-@menu
-* C to Scheme::
-* Scheme to C::
-@end menu
-
-@node C to Scheme
-@subsection C to Scheme
-
-@deftypefun SCM gh_bool2scm (int @var{x})
-Returns @code{#f} if @var{x} is zero, @code{#t} otherwise.
-@end deftypefun
-
-@deftypefun SCM gh_ulong2scm (unsigned long @var{x})
-@deftypefunx SCM gh_long2scm (long @var{x})
-@deftypefunx SCM gh_double2scm (double @var{x})
-@deftypefunx SCM gh_char2scm (char @var{x})
-Returns a Scheme object with the value of the C quantity @var{x}.
-@end deftypefun
-
-@deftypefun SCM gh_str2scm (char *@var{s}, int @var{len})
-Returns a new Scheme string with the (not necessarily null-terminated) C
-array @var{s} data.
-@end deftypefun
-
-@deftypefun SCM gh_str02scm (char *@var{s})
-Returns a new Scheme string with the null-terminated C string @var{s}
-data.
-@end deftypefun
-
-@deftypefun SCM gh_set_substr (char *@var{src}, SCM @var{dst}, int @var{start}, int @var{len})
-Copy @var{len} characters at @var{src} into the @emph{existing} Scheme
-string @var{dst}, starting at @var{start}. @var{start} is an index into
-@var{dst}; zero means the beginning of the string.
-
-If @var{start} + @var{len} is off the end of @var{dst}, signal an
-out-of-range error.
-@end deftypefun
-
-@deftypefun SCM gh_symbol2scm (char *@var{name})
-Given a null-terminated string @var{name}, return the symbol with that
-name.
-@end deftypefun
-
-@deftypefun SCM gh_ints2scm (int *@var{dptr}, int @var{n})
-@deftypefunx SCM gh_doubles2scm (double *@var{dptr}, int @var{n})
-Make a scheme vector containing the @var{n} ints or doubles at memory
-location @var{dptr}.
-@end deftypefun
-
-@deftypefun SCM gh_chars2byvect (char *@var{dptr}, int @var{n})
-@deftypefunx SCM gh_shorts2svect (short *@var{dptr}, int @var{n})
-@deftypefunx SCM gh_longs2ivect (long *@var{dptr}, int @var{n})
-@deftypefunx SCM gh_ulongs2uvect (ulong *@var{dptr}, int @var{n})
-@deftypefunx SCM gh_floats2fvect (float *@var{dptr}, int @var{n})
-@deftypefunx SCM gh_doubles2dvect (double *@var{dptr}, int @var{n})
-Make a scheme uniform vector containing the @var{n} chars, shorts,
-longs, unsigned longs, floats or doubles at memory location @var{dptr}.
-@end deftypefun
-
-
-
-@node Scheme to C
-@subsection Scheme to C
-
-@deftypefun int gh_scm2bool (SCM @var{obj})
-@deftypefunx {unsigned long} gh_scm2ulong (SCM @var{obj})
-@deftypefunx long gh_scm2long (SCM @var{obj})
-@deftypefunx double gh_scm2double (SCM @var{obj})
-@deftypefunx int gh_scm2char (SCM @var{obj})
-These routines convert the Scheme object to the given C type.
-@end deftypefun
-
-@deftypefun char *gh_scm2newstr (SCM @var{str}, int *@var{lenp})
-Given a Scheme string @var{str}, return a pointer to a new copy of its
-contents, followed by a null byte. If @var{lenp} is non-null, set
-@code{*@var{lenp}} to the string's length.
-
-This function uses malloc to obtain storage for the copy; the caller is
-responsible for freeing it.
-
-Note that Scheme strings may contain arbitrary data, including null
-characters. This means that null termination is not a reliable way to
-determine the length of the returned value. However, the function
-always copies the complete contents of @var{str}, and sets @var{*lenp}
-to the true length of the string (when @var{lenp} is non-null).
-@end deftypefun
-
-
-@deftypefun void gh_get_substr (SCM str, char *return_str, int *lenp)
-Copy @var{len} characters at @var{start} from the Scheme string
-@var{src} to memory at @var{dst}. @var{start} is an index into
-@var{src}; zero means the beginning of the string. @var{dst} has
-already been allocated by the caller.
-
-If @var{start} + @var{len} is off the end of @var{src}, signal an
-out-of-range error.
-@end deftypefun
-
-@deftypefun char *gh_symbol2newstr (SCM @var{sym}, int *@var{lenp})
-Takes a Scheme symbol and returns a string of the form
-@code{"'symbol-name"}. If @var{lenp} is non-null, the string's length
-is returned in @code{*@var{lenp}}.
-
-This function uses malloc to obtain storage for the returned string; the
-caller is responsible for freeing it.
-@end deftypefun
-
-@deftypefun char *gh_scm2chars (SCM @var{vector}, chars *@var{result})
-@deftypefunx short *gh_scm2shorts (SCM @var{vector}, short *@var{result})
-@deftypefunx long *gh_scm2longs (SCM @var{vector}, long *@var{result})
-@deftypefunx float *gh_scm2floats (SCM @var{vector}, float *@var{result})
-@deftypefunx double *gh_scm2doubles (SCM @var{vector}, double *@var{result})
-Copy the numbers in @var{vector} to the array pointed to by @var{result}
-and return it. If @var{result} is NULL, allocate a double array large
-enough.
-
-@var{vector} can be an ordinary vector, a weak vector, or a signed or
-unsigned uniform vector of the same type as the result array. For
-chars, @var{vector} can be a string or substring. For floats and
-doubles, @var{vector} can contain a mix of inexact and integer values.
-
-If @var{vector} is of unsigned type and contains values too large to fit
-in the signed destination array, those values will be wrapped around,
-that is, data will be copied as if the destination array was unsigned.
-@end deftypefun
-
-
-@node Type predicates
-@section Type predicates
-
-These C functions mirror Scheme's type predicate procedures with one
-important difference. The C routines return C boolean values (0 and 1)
-instead of @code{SCM_BOOL_T} and @code{SCM_BOOL_F}.
-
-The Scheme notational convention of putting a @code{?} at the end of
-predicate procedure names is mirrored in C by placing @code{_p} at the
-end of the procedure. For example, @code{(pair? ...)} maps to
-@code{gh_pair_p(...)}.
-
-@deftypefun int gh_boolean_p (SCM @var{val})
-Returns 1 if @var{val} is a boolean, 0 otherwise.
-@end deftypefun
-
-@deftypefun int gh_symbol_p (SCM @var{val})
-Returns 1 if @var{val} is a symbol, 0 otherwise.
-@end deftypefun
-
-@deftypefun int gh_char_p (SCM @var{val})
-Returns 1 if @var{val} is a char, 0 otherwise.
-@end deftypefun
-
-@deftypefun int gh_vector_p (SCM @var{val})
-Returns 1 if @var{val} is a vector, 0 otherwise.
-@end deftypefun
-
-@deftypefun int gh_pair_p (SCM @var{val})
-Returns 1 if @var{val} is a pair, 0 otherwise.
-@end deftypefun
-
-@deftypefun int gh_procedure_p (SCM @var{val})
-Returns 1 if @var{val} is a procedure, 0 otherwise.
-@end deftypefun
-
-@deftypefun int gh_list_p (SCM @var{val})
-Returns 1 if @var{val} is a list, 0 otherwise.
-@end deftypefun
-
-@deftypefun int gh_inexact_p (SCM @var{val})
-Returns 1 if @var{val} is an inexact number, 0 otherwise.
-@end deftypefun
-
-@deftypefun int gh_exact_p (SCM @var{val})
-Returns 1 if @var{val} is an exact number, 0 otherwise.
-@end deftypefun
-
-
-@node Equality predicates
-@section Equality predicates
-
-These C functions mirror Scheme's equality predicate procedures with one
-important difference. The C routines return C boolean values (0 and 1)
-instead of @code{SCM_BOOL_T} and @code{SCM_BOOL_F}.
-
-The Scheme notational convention of putting a @code{?} at the end of
-predicate procedure names is mirrored in C by placing @code{_p} at the
-end of the procedure. For example, @code{(equal? ...)} maps to
-@code{gh_equal_p(...)}.
-
-@deftypefun int gh_eq_p (SCM x, SCM y)
-Returns 1 if @var{x} and @var{y} are equal in the sense of Scheme's
-@code{eq?} predicate, 0 otherwise.
-@end deftypefun
-
-@deftypefun int gh_eqv_p (SCM x, SCM y)
-Returns 1 if @var{x} and @var{y} are equal in the sense of Scheme's
-@code{eqv?} predicate, 0 otherwise.
-@end deftypefun
-
-@deftypefun int gh_equal_p (SCM x, SCM y)
-Returns 1 if @var{x} and @var{y} are equal in the sense of Scheme's
-@code{equal?} predicate, 0 otherwise.
-@end deftypefun
-
-@deftypefun int gh_string_equal_p (SCM @var{s1}, SCM @var{s2})
-Returns 1 if the strings @var{s1} and @var{s2} are equal, 0 otherwise.
-@end deftypefun
-
-@deftypefun int gh_null_p (SCM @var{l})
-Returns 1 if @var{l} is an empty list or pair; 0 otherwise.
-@end deftypefun
-
-
-@node Memory allocation and garbage collection
-@section Memory allocation and garbage collection
-
-@c [FIXME: flesh this out with some description of garbage collection in
-@c scm/guile]
-
-@c @deftypefun SCM gh_mkarray (int size)
-@c Allocate memory for a Scheme object in a garbage-collector-friendly
-@c manner.
-@c @end deftypefun
-
-
-@node Calling Scheme procedures from C
-@section Calling Scheme procedures from C
-
-Many of the Scheme primitives are available in the @code{gh_}
-interface; they take and return objects of type SCM, and one could
-basically use them to write C code that mimics Scheme code.
-
-I will list these routines here without much explanation, since what
-they do is the same as documented in @ref{Standard procedures, R5RS, ,
-r5rs, R5RS}. But I will point out that when a procedure takes a
-variable number of arguments (such as @code{gh_list}), you should pass
-the constant @var{SCM_UNDEFINED} from C to signify the end of the list.
-
-@deftypefun SCM gh_define (char *@var{name}, SCM @var{val})
-Corresponds to the Scheme @code{(define name val)}: it binds a value to
-the given name (which is a C string). Returns the new object.
-@end deftypefun
-
-@heading Pairs and lists
-
-@deftypefun SCM gh_cons (SCM @var{a}, SCM @var{b})
-@deftypefunx SCM gh_list (SCM l0, SCM l1, ... , SCM_UNDEFINED)
-These correspond to the Scheme @code{(cons a b)} and @code{(list l0 l1
-...)} procedures. Note that @code{gh_list()} is a C macro that invokes
-@code{scm_listify()}.
-@end deftypefun
-
-@deftypefun SCM gh_car (SCM @var{obj})
-@deftypefunx SCM gh_cdr (SCM @var{obj})
-@dots{}
-
-@deftypefunx SCM gh_c[ad][ad][ad][ad]r (SCM @var{obj})
-These correspond to the Scheme @code{(caadar ls)} procedures etc @dots{}
-@end deftypefun
-
-@deftypefun SCM gh_set_car_x(SCM @var{pair}, SCM @var{value})
-Modifies the CAR of @var{pair} to be @var{value}. This is equivalent to
-the Scheme procedure @code{(set-car! ...)}.
-@end deftypefun
-
-@deftypefun SCM gh_set_cdr_x(SCM @var{pair}, SCM @var{value})
-Modifies the CDR of @var{pair} to be @var{value}. This is equivalent to
-the Scheme procedure @code{(set-cdr! ...)}.
-@end deftypefun
-
-@deftypefun {unsigned long} gh_length (SCM @var{ls})
-Returns the length of the list.
-@end deftypefun
-
-@deftypefun SCM gh_append (SCM @var{args})
-@deftypefunx SCM gh_append2 (SCM @var{l1}, SCM @var{l2})
-@deftypefunx SCM gh_append3 (SCM @var{l1}, SCM @var{l2}, @var{l3})
-@deftypefunx SCM gh_append4 (SCM @var{l1}, SCM @var{l2}, @var{l3}, @var{l4})
-@code{gh_append()} takes @var{args}, which is a list of lists
-@code{(list1 list2 ...)}, and returns a list containing all the elements
-of the individual lists.
-
-A typical invocation of @code{gh_append()} to append 5 lists together
-would be
-@smallexample
- gh_append(gh_list(l1, l2, l3, l4, l5, SCM_UNDEFINED));
-@end smallexample
-
-The functions @code{gh_append2()}, @code{gh_append2()},
-@code{gh_append3()} and @code{gh_append4()} are convenience routines to
-make it easier for C programs to form the list of lists that goes as an
-argument to @code{gh_append()}.
-@end deftypefun
-
-@deftypefun SCM gh_reverse (SCM @var{ls})
-Returns a new list that has the same elements as @var{ls} but in the
-reverse order. Note that this is implemented as a macro which calls
-@code{scm_reverse()}.
-@end deftypefun
-
-@deftypefun SCM gh_list_tail (SCM @var{ls}, SCM @var{k})
-Returns the sublist of @var{ls} with the last @var{k} elements.
-@end deftypefun
-
-@deftypefun SCM gh_list_ref (SCM @var{ls}, SCM @var{k})
-Returns the @var{k}th element of the list @var{ls}.
-@end deftypefun
-
-@deftypefun SCM gh_memq (SCM @var{x}, SCM @var{ls})
-@deftypefunx SCM gh_memv (SCM @var{x}, SCM @var{ls})
-@deftypefunx SCM gh_member (SCM @var{x}, SCM @var{ls})
-These functions return the first sublist of @var{ls} whose CAR is
-@var{x}. They correspond to @code{(memq x ls)}, @code{(memv x ls)} and
-@code{(member x ls)}, and hence use (respectively) @code{eq?},
-@code{eqv?} and @code{equal?} to do comparisons.
-
-If @var{x} does not appear in @var{ls}, the value @code{SCM_BOOL_F} (not
-the empty list) is returned.
-
-Note that these functions are implemented as macros which call
-@code{scm_memq()}, @code{scm_memv()} and @code{scm_member()}
-respectively.
-@end deftypefun
-
-@deftypefun SCM gh_assq (SCM @var{x}, SCM @var{alist})
-@deftypefunx SCM gh_assv (SCM @var{x}, SCM @var{alist})
-@deftypefunx SCM gh_assoc (SCM @var{x}, SCM @var{alist})
-These functions search an @dfn{association list} (list of pairs)
-@var{alist} for the first pair whose CAR is @var{x}, and they return
-that pair.
-
-If no pair in @var{alist} has @var{x} as its CAR, the value
-@code{SCM_BOOL_F} (not the empty list) is returned.
-
-Note that these functions are implemented as macros which call
-@code{scm_assq()}, @code{scm_assv()} and @code{scm_assoc()}
-respectively.
-@end deftypefun
-
-
-@heading Symbols
-
-@c @deftypefun SCM gh_symbol (SCM str, SCM len)
-@c @deftypefunx SCM gh_tmp_symbol (SCM str, SCM len)
-@c Takes the given string @var{str} of length @var{len} and returns a
-@c symbol corresponding to that string.
-@c @end deftypefun
-
-
-@heading Vectors
-
-@deftypefun SCM gh_make_vector (SCM @var{n}, SCM @var{fill})
-@deftypefunx SCM gh_vector (SCM @var{ls})
-@deftypefunx SCM gh_vector_ref (SCM @var{v}, SCM @var{i})
-@deftypefunx SCM gh_vector_set (SCM @var{v}, SCM @var{i}, SCM @var{val})
-@deftypefunx {unsigned long} gh_vector_length (SCM @var{v})
-@deftypefunx SCM gh_list_to_vector (SCM @var{ls})
-These correspond to the Scheme @code{(make-vector n fill)},
-@code{(vector a b c ...)} @code{(vector-ref v i)} @code{(vector-set v i
-value)} @code{(vector-length v)} @code{(list->vector ls)} procedures.
-
-The correspondence is not perfect for @code{gh_vector}: this routine
-takes a list @var{ls} instead of the individual list elements, thus
-making it identical to @code{gh_list_to_vector}.
-
-There is also a difference in gh_vector_length: the value returned is a
-C @code{unsigned long} instead of an SCM object.
-@end deftypefun
-
-
-@heading Procedures
-
-@c @deftypefun SCM gh_make_subr (SCM (*@var{fn})(), int @var{req}, int @var{opt}, int @var{restp}, char *@var{sym})
-@c Make the C function @var{fn} available to Scheme programs. The function
-@c will be bound to the symbol @var{sym}. The arguments @var{req},
-@c @var{opt} and @var{restp} describe @var{fn}'s calling conventions. The
-@c function must take @var{req} required arguments and may take @var{opt}
-@c optional arguments. Any optional arguments which are not supplied by
-@c the caller will be bound to @var{SCM_UNSPECIFIED}. If @var{restp} is
-@c non-zero, it means that @var{fn} may be called with an arbitrary number
-@c of arguments, and that any extra arguments supplied by the caller will
-@c be passed to @var{fn} as a list. The @var{restp} argument is exactly
-@c like Scheme's @code{(lambda (arg1 arg2 . arglist))} calling convention.
-@c
-@c For example, the procedure @code{read-line}, which takes optional
-@c @var{port} and @var{handle-delim} arguments, would be declared like so:
-@c
-@c @example
-@c SCM scm_read_line (SCM port, SCM handle_delim);
-@c gh_make_subr (scm_read_line, 0, 2, 0, "read-line");
-@c @end example
-@c
-@c The @var{req} argument to @code{gh_make_subr} is 0 to indicate that
-@c there are no required arguments, so @code{read-line} may be called
-@c without any arguments at all. The @var{opt} argument is 2, to indicate
-@c that both the @var{port} and @var{handle_delim} arguments to
-@c @code{scm_read_line} are optional, and will be bound to
-@c @code{SCM_UNSPECIFIED} if the calling program does not supply them.
-@c Because the @var{restp} argument is 0, this function may not be called
-@c with more than two arguments.
-@c @end deftypefun
-
-@deftypefun SCM gh_apply (SCM proc, SCM args)
-Call the Scheme procedure @var{proc}, with the elements of @var{args} as
-arguments. @var{args} must be a proper list.
-@end deftypefun
-
-@deftypefun SCM gh_call0 (SCM proc)
-@deftypefunx SCM gh_call1 (SCM proc, SCM arg)
-@deftypefunx SCM gh_call2 (SCM proc, SCM arg1, SCM arg2)
-@deftypefunx SCM gh_call3 (SCM proc, SCM arg1, SCM arg2, SCM arg3)
-Call the Scheme procedure @var{proc} with no arguments
-(@code{gh_call0}), one argument (@code{gh_call1}), and so on. You can
-get the same effect by wrapping the arguments up into a list, and
-calling @code{gh_apply}; Guile provides these functions for convenience.
-@end deftypefun
-
-
-@deftypefun SCM gh_catch (SCM key, SCM thunk, SCM handler)
-@deftypefunx SCM gh_throw (SCM key, SCM args)
-Corresponds to the Scheme @code{catch} and @code{throw} procedures,
-which in Guile are provided as primitives.
-@end deftypefun
-
-@c [FIXME: must add the I/O section in gscm.h]
-
-@deftypefun SCM gh_is_eq (SCM a, SCM b)
-@deftypefunx SCM gh_is_eqv (SCM a, SCM b)
-@deftypefunx SCM gh_is_equal (SCM a, SCM b)
-These correspond to the Scheme @code{eq?}, @code{eqv?} and @code{equal?}
-predicates.
-@end deftypefun
-
-@deftypefun int gh_obj_length (SCM @var{obj})
-Returns the raw object length.
-@end deftypefun
-
-@heading Data lookup
-
-For now I just include Tim Pierce's comments from the @file{gh_data.c}
-file; it should be organized into a documentation of the two functions
-here.
-
-@smallexample
-/* Data lookups between C and Scheme
-
- Look up a symbol with a given name, and return the object to which
- it is bound. gh_lookup examines the Guile top level, and
- gh_module_lookup checks the module name space specified by the
- `vec' argument.
-
- The return value is the Scheme object to which SNAME is bound, or
- SCM_UNDEFINED if SNAME is not bound in the given context. [FIXME:
- should this be SCM_UNSPECIFIED? Can a symbol ever legitimately be
- bound to SCM_UNDEFINED or SCM_UNSPECIFIED? What is the difference?
- -twp] */
-@end smallexample
-
-
-@node Mixing gh and scm APIs
-@section Mixing gh and scm APIs
-
-
-@node scm transition summary
-@section Transitioning to the scm Interface
-
-The following table summarizes the available information on how to
-transition from the GH to the scm interface. Where transitioning is not
-completely straightforward, the table includes a reference to more
-detailed documentation in the preceding sections.
-
-@table @asis
-@item Header file
-Use @code{#include <libguile.h>} instead of @code{#include
-<guile/gh.h>}.
-
-@item Compiling and Linking
-Use @code{guile-config} to pick up the flags required to compile C or
-C++ code that uses @code{libguile}, like so
-
-@smallexample
-$(CC) -o prog.o -c prog.c `guile-config compile`
-@end smallexample
-
-If you are using libtool to link your executables, just use
-@code{-lguile} in your link command. Libtool will expand this into
-the needed linker options automatically. If you are not using
-libtool, use the @code{guile-config} program to query the needed
-options explicitly. A linker command like
-
-@smallexample
-$(CC) -o prog prog.o `guile-config link`
-@end smallexample
-
-should be all that is needed. To link shared libraries that will be
-used as Guile Extensions, use libtool to control both the compilation
-and the link stage.
-
-@item The @code{SCM} type
-No change: the scm interface also uses this type to represent an
-arbitrary Scheme value.
-
-@item @code{SCM_BOOL_F} and @code{SCM_BOOL_T}
-No change.
-
-@item @code{SCM_UNSPECIFIED} and @code{SCM_UNDEFINED}
-No change.
-
-@item @code{gh_enter}
-Use @code{scm_boot_guile} instead, but note that @code{scm_boot_guile}
-has a slightly different calling convention from @code{gh_enter}:
-@code{scm_boot_guile}, and the main program function that you specify
-for @code{scm_boot_guile} to call, both take an additional @var{closure}
-parameter. @ref{Guile Initialization Functions} for more details.
-
-@item @code{gh_repl}
-Use @code{scm_shell} instead.
-
-@item @code{gh_init}
-Use @code{scm_init_guile} instead.
-
-@item @code{gh_eval_str}
-Use @code{scm_c_eval_string} instead.
-
-@item @code{gh_eval_file} or @code{gh_load}
-Use @code{scm_c_primitive_load} instead.
-
-@item @code{gh_new_procedure}
-Use @code{scm_c_define_gsubr} instead, but note that the arguments are
-in a different order: for @code{scm_c_define_gsubr} the C function
-pointer is the last argument. @ref{A Sample Guile Extension} for an
-example.
-
-@item @code{gh_defer_ints} and @code{gh_allow_ints}
-Use @code{SCM_DEFER_INTS} and @code{SCM_ALLOW_INTS} instead. Note that
-these macros are used without parentheses, as in @code{SCM_DEFER_INTS;}.
-
-@item @code{gh_bool2scm}
-Use @code{SCM_BOOL} instead.
-
-@item @code{gh_ulong2scm}
-Use @code{scm_ulong2num} instead.
-
-@item @code{gh_long2scm}
-Use @code{scm_long2num} instead.
-
-@item @code{gh_double2scm}
-Use @code{scm_make_real} instead.
-
-@item @code{gh_char2scm}
-Use @code{SCM_MAKE_CHAR} instead.
-
-@item @code{gh_str2scm}
-Use @code{scm_mem2string} instead.
-
-@item @code{gh_str02scm}
-Use @code{scm_makfrom0str} instead.
-
-@item @code{gh_set_substr}
-No direct scm equivalent. [FIXME]
-
-@item @code{gh_symbol2scm}
-Use @code{scm_str2symbol} instead. [FIXME: inconsistent naming,
-should be @code{scm_str02symbol}.]
-
-@item @code{gh_ints2scm} and @code{gh_doubles2scm}
-Use @code{scm_c_ints2scm} and @code{scm_c_doubles2scm} instead.
-
-@item @code{gh_chars2byvect} and @code{gh_shorts2svect}
-Use @code{scm_c_chars2byvect} and @code{scm_c_shorts2svect} instead.
-
-@item @code{gh_longs2ivect} and @code{gh_ulongs2uvect}
-Use @code{scm_c_longs2ivect} and @code{scm_c_ulongs2uvect} instead.
-
-@item @code{gh_floats2fvect} and @code{gh_doubles2dvect}
-Use @code{scm_c_floats2fvect} and @code{scm_c_doubles2dvect} instead.
-
-@item @code{gh_scm2bool}
-Use @code{SCM_NFALSEP} instead.
-
-@item @code{gh_scm2int}
-Replace @code{gh_scm2int (@var{obj})} by
-@example
-scm_num2int (@var{obj}, SCM_ARG1, @var{str})
-@end example
-where @var{str} is a C string that describes the context of the call.
-
-@item @code{gh_scm2ulong}
-Replace @code{gh_scm2ulong (@var{obj})} by
-@example
-scm_num2ulong (@var{obj}, SCM_ARG1, @var{str})
-@end example
-where @var{str} is a C string that describes the context of the call.
-
-@item @code{gh_scm2long}
-Replace @code{gh_scm2long (@var{obj})} by
-@example
-scm_num2long (@var{obj}, SCM_ARG1, @var{str})
-@end example
-where @var{str} is a C string that describes the context of the call.
-
-@item @code{gh_scm2double}
-Replace @code{gh_scm2double (@var{obj})} by
-@example
-scm_num2dbl (@var{obj}, @var{str})
-@end example
-where @var{str} is a C string that describes the context of the call.
-
-@item @code{gh_scm2char}
-Use the @code{SCM_CHAR} macro instead, but note that @code{SCM_CHAR}
-does not check that its argument is actually a character. To check that
-a @code{SCM} value is a character before using @code{SCM_CHAR} to
-extract the character value, use the @code{SCM_VALIDATE_CHAR} macro.
-
-@item @code{gh_scm2newstr}
-Instead of @code{gh_scm2newstr (@var{obj}, @var{lenp})} use
-@code{scm_c_string2str (@var{obj}, @var{str}, @var{lenp})}. With the
-additional @var{str} argument the user can pass a pre-allocated memory
-chunk or leave it passing NULL.
-
-@item @code{gh_get_substr}
-Use the @code{scm_c_substring2str (@var{obj}, @var{str}, @var{start},
-@var{len})} function instead.
-
-@item @code{gh_symbol2newstr}
-Use the @code{scm_c_symbol2str (@var{obj}, @var{str}, @var{lenp})} function
-instead. With the additional @var{str} argument the user can pass a
-pre-allocated memory chunk or leave it passing NULL.
-
-@item @code{gh_scm2chars}
-Use @code{scm_c_scm2chars} instead.
-
-@item @code{gh_scm2shorts} and @code{gh_scm2longs}
-Use @code{scm_c_shorts2scm} and @code{scm_c_longs2scm} instead.
-
-@item @code{gh_scm2floats} and @code{gh_scm2doubles}
-Use @code{scm_c_floats2scm} and @code{scm_c_doubles2scm} instead.
-
-@item @code{gh_boolean_p}
-Use the @code{SCM_BOOLP} macro instead, or replace @code{gh_boolean_p
-(@var{obj})} by
-@example
-SCM_NFALSEP (scm_boolean_p (@var{obj}))
-@end example
-
-@item @code{gh_symbol_p}
-Use the @code{SCM_SYMBOLP} macro instead, or replace @code{gh_symbol_p
-(@var{obj})} by
-@example
-SCM_NFALSEP (scm_symbol_p (@var{obj}))
-@end example
-
-@item @code{gh_char_p}
-Use the @code{SCM_CHARP} macro instead, or replace @code{gh_char_p
-(@var{obj})} by
-@example
-SCM_NFALSEP (scm_char_p (@var{obj}))
-@end example
-
-@item @code{gh_vector_p}
-Use the @code{SCM_VECTORP} macro instead, or replace @code{gh_vector_p
-(@var{obj})} by
-@example
-SCM_NFALSEP (scm_vector_p (@var{obj}))
-@end example
-
-@item @code{gh_pair_p}
-Use the @code{SCM_CONSP} macro instead, or replace @code{gh_pair_p
-(@var{obj})} by
-@example
-SCM_NFALSEP (scm_pair_p (@var{obj}))
-@end example
-
-@item @code{gh_number_p}
-Use the @code{SCM_NUMBERP} macro instead, or replace @code{gh_number_p
-(@var{obj})} by
-@example
-SCM_NFALSEP (scm_number_p (@var{obj}))
-@end example
-
-@item @code{gh_string_p}
-Use the @code{SCM_STRINGP} macro instead, or replace @code{gh_string_p
-(@var{obj})} by
-@example
-SCM_NFALSEP (scm_string_p (@var{obj}))
-@end example
-
-@item @code{gh_procedure_p}
-Replace @code{gh_procedure_p (@var{obj})} by
-@example
-SCM_NFALSEP (scm_procedure_p (@var{obj}))
-@end example
-
-@item @code{gh_list_p}
-Replace @code{gh_list_p (@var{obj})} by
-@example
-SCM_NFALSEP (scm_list_p (@var{obj}))
-@end example
-
-@item @code{gh_inexact_p}
-Use the @code{SCM_INEXACTP} macro instead, or replace @code{gh_inexact_p
-(@var{obj})} by
-@example
-SCM_NFALSEP (scm_inexact_p (@var{obj}))
-@end example
-
-@item @code{gh_exact_p}
-Replace @code{gh_exact_p (@var{obj})} by
-@example
-SCM_NFALSEP (scm_exact_p (@var{obj}))
-@end example
-
-@item @code{gh_eq_p}
-Use the @code{SCM_EQ_P} macro instead, or replace @code{gh_eq_p
-(@var{x}, @var{y})} by
-@example
-SCM_NFALSEP (scm_eq_p (@var{x}, @var{y}))
-@end example
-
-@item @code{gh_eqv_p}
-Replace @code{gh_eqv_p (@var{x}, @var{y})} by
-@example
-SCM_NFALSEP (scm_eqv_p (@var{x}, @var{y}))
-@end example
-
-@item @code{gh_equal_p}
-Replace @code{gh_equal_p (@var{x}, @var{y})} by
-@example
-SCM_NFALSEP (scm_equal_p (@var{x}, @var{y}))
-@end example
-
-@item @code{gh_string_equal_p}
-Replace @code{gh_string_equal_p (@var{x}, @var{y})} by
-@example
-SCM_NFALSEP (scm_string_equal_p (@var{x}, @var{y}))
-@end example
-
-@item @code{gh_null_p}
-Use the @code{SCM_NULLP} macro instead, or replace @code{gh_null_p
-(@var{obj})} by
-@example
-SCM_NFALSEP (scm_null_p (@var{obj}))
-@end example
-
-@item @code{gh_cons}
-Use @code{scm_cons} instead.
-
-@item @code{gh_car} and @code{gh_cdr}
-Use the @code{SCM_CAR} and @code{SCM_CDR} macros instead.
-
-@item @code{gh_cxxr} and @code{gh_cxxxr}
-(Where each x is either @samp{a} or @samp{d}.) Use the corresponding
-@code{SCM_CXXR} or @code{SCM_CXXXR} macro instead.
-
-@item @code{gh_set_car_x} and @code{gh_set_cdr_x}
-Use @code{scm_set_car_x} and @code{scm_set_cdr_x} instead.
-
-@item @code{gh_list}
-Use @code{scm_listify} instead.
-
-@item @code{gh_length}
-Replace @code{gh_length (@var{lst})} by
-@example
-scm_num2ulong (scm_length (@var{lst}), SCM_ARG1, @var{str})
-@end example
-where @var{str} is a C string that describes the context of the call.
-
-@item @code{gh_append}
-Use @code{scm_append} instead.
-
-@item @code{gh_append2}, @code{gh_append3}, @code{gh_append4}
-Replace @code{gh_append@var{N} (@var{l1}, @dots{}, @var{lN})} by
-@example
-scm_append (scm_listify (@var{l1}, @dots{}, @var{lN}, SCM_UNDEFINED))
-@end example
-
-@item @code{gh_reverse}
-Use @code{scm_reverse} instead.
-
-@item @code{gh_list_tail} and @code{gh_list_ref}
-Use @code{scm_list_tail} and @code{scm_list_ref} instead.
-
-@item @code{gh_memq}, @code{gh_memv} and @code{gh_member}
-Use @code{scm_memq}, @code{scm_memv} and @code{scm_member} instead.
-
-@item @code{gh_assq}, @code{gh_assv} and @code{gh_assoc}
-Use @code{scm_assq}, @code{scm_assv} and @code{scm_assoc} instead.
-
-@item @code{gh_make_vector}
-Use @code{scm_make_vector} instead.
-
-@item @code{gh_vector} or @code{gh_list_to_vector}
-Use @code{scm_vector} instead.
-
-@item @code{gh_vector_ref} and @code{gh_vector_set_x}
-Use @code{scm_vector_ref} and @code{scm_vector_set_x} instead.
-
-@item @code{gh_vector_length}
-Use the @code{SCM_VECTOR_LENGTH} macro instead.
-
-@item @code{gh_apply}
-Use @code{scm_apply} instead, but note that @code{scm_apply} takes an
-additional third argument that you should set to @code{SCM_EOL}.
-
-@end table