( A Sample Guile Extension

Info Catalog ( Writing Extensions for Guile
 5.4.1 A Sample Guile Extension
 This section explains how to make the Bessel functions of the C library
 available to Scheme.  First we need to write the appropriate glue code
 to convert the arguments and return values of the functions from Scheme
 to C and back.  Additionally, we need a function that will add them to
 the set of Guile primitives.  Because this is just an example, we will
 only implement this for the `j0' function.
    Consider the following file `bessel.c'.
      #include <math.h>
      #include <libguile.h>
      j0_wrapper (SCM x)
        return scm_make_real (j0 (scm_num2dbl (x, "j0")));
      init_bessel ()
        scm_c_define_gsubr ("j0", 1, 0, 0, j0_wrapper);
    This C source file needs to be compiled into a shared library.  Here
 is how to do it on GNU/Linux:
      gcc -shared -o -fPIC bessel.c
    For creating shared libraries portably, we recommend the use of `GNU
    A shared library can be loaded into a running Guile process with the
 function `load-extension'.  In addition to the name of the library to
 load, this function also expects the name of function from that library
 that will be called to initialize it.  For our example, we are going to
 call the function `init_bessel' which will make `j0_wrapper' available
 to Scheme programs with the name `j0'.  Note that we do not specify a
 filename extension such as `.so' when invoking `load-extension'.  The
 right extension for the host platform will be provided automatically.
      (load-extension "libguile-bessel" "init_bessel")
      (j0 2)
      => 0.223890779141236
    For this to work, `load-extension' must be able to find
 `libguile-bessel', of course.  It will look in the places that are
 usual for your operating system, and it will additionally look into the
 directories listed in the `LTDL_LIBRARY_PATH' environment variable.
    To see how these Guile extensions via shared libraries relate to the
 module system, see below  Intro to Modules and Extensions.
Info Catalog ( Writing Extensions for Guile
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