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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;
    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);

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)