Warning: This is the manual of the legacy Guile 2.2 series. You may want to read the manual of the current stable series instead.

2.3 Linking Guile into Programs

The Guile interpreter is available as an object library, to be linked into applications using Scheme as a configuration or extension language.

Here is simple-guile.c, source code for a program that will produce a complete Guile interpreter. In addition to all usual functions provided by Guile, it will also offer the function my-hostname.

#include <stdlib.h>
#include <libguile.h>

static SCM
my_hostname (void)
{
  char *s = getenv ("HOSTNAME");
  if (s == NULL)
    return SCM_BOOL_F;
  else
    return scm_from_locale_string (s);
}

static void
inner_main (void *data, int argc, char **argv)
{
  scm_c_define_gsubr ("my-hostname", 0, 0, 0, my_hostname);
  scm_shell (argc, argv);
}

int
main (int argc, char **argv)
{
  scm_boot_guile (argc, argv, inner_main, 0);
  return 0; /* never reached */
}

When Guile is correctly installed on your system, the above program can be compiled and linked like this:

$ gcc -o simple-guile simple-guile.c \
    `pkg-config --cflags --libs guile-2.2`

When it is run, it behaves just like the guile program except that you can also call the new my-hostname function.

$ ./simple-guile
scheme@(guile-user)> (+ 1 2 3)
$1 = 6
scheme@(guile-user)> (my-hostname)
"burns"