4.1.2 A Sample Guile Main Program

Here is simple-guile.c, source code for a main and an inner_main function that will produce a complete Guile interpreter.

     /* simple-guile.c --- how to start up the Guile
        interpreter from C code.  */
     
     /* Get declarations for all the scm_ functions.  */
     #include <libguile.h>
     
     static void
     inner_main (void *closure, int argc, char **argv)
     {
       /* module initializations would go here */
       scm_shell (argc, argv);
     }
     
     int
     main (int argc, char **argv)
     {
       scm_boot_guile (argc, argv, inner_main, 0);
       return 0; /* never reached */
     }

The main function calls scm_boot_guile to initialize Guile, passing it inner_main. Once scm_boot_guile is ready, it invokes inner_main, which calls scm_shell to process the command-line arguments in the usual way.

Here is a Makefile which you can use to compile the above program. It uses guile-config to learn about the necessary compiler and linker flags.

     # Use GCC, if you have it installed.
     CC=gcc
     
     # Tell the C compiler where to find <libguile.h>
     CFLAGS=`guile-config compile`
     
     # Tell the linker what libraries to use and where to find them.
     LIBS=`guile-config link`
     
     simple-guile: simple-guile.o
             ${CC} simple-guile.o ${LIBS} -o simple-guile
     
     simple-guile.o: simple-guile.c
             ${CC} -c ${CFLAGS} simple-guile.c

If you are using the GNU Autoconf package to make your application more portable, Autoconf will settle many of the details in the Makefile above automatically, making it much simpler and more portable; we recommend using Autoconf with Guile. Guile also provides the GUILE_FLAGS macro for autoconf that performs all necessary checks. Here is a configure.in file for simple-guile that uses this macro. Autoconf can use this file as a template to generate a configure script. In order for Autoconf to find the GUILE_FLAGS macro, you will need to run aclocal first (see Invoking aclocal).

     AC_INIT(simple-guile.c)
     
     # Find a C compiler.
     AC_PROG_CC
     
     # Check for Guile
     GUILE_FLAGS
     
     # Generate a Makefile, based on the results.
     AC_OUTPUT(Makefile)

Here is a Makefile.in template, from which the configure script produces a Makefile customized for the host system:

     # The configure script fills in these values.
     CC=@CC@
     CFLAGS=@GUILE_CFLAGS@
     LIBS=@GUILE_LDFLAGS@
     
     simple-guile: simple-guile.o
             ${CC} simple-guile.o ${LIBS} -o simple-guile
     simple-guile.o: simple-guile.c
             ${CC} -c ${CFLAGS} simple-guile.c

The developer should use Autoconf to generate the configure script from the configure.in template, and distribute configure with the application. Here's how a user might go about building the application:

     $ ls
     Makefile.in     configure*      configure.in    simple-guile.c
     $ ./configure
     creating cache ./config.cache
     checking for gcc... (cached) gcc
     checking whether the C compiler (gcc  ) works... yes
     checking whether the C compiler (gcc  ) is a cross-compiler... no
     checking whether we are using GNU C... (cached) yes
     checking whether gcc accepts -g... (cached) yes
     checking for Guile... yes
     creating ./config.status
     creating Makefile
     $ make
     gcc -c -I/usr/local/include simple-guile.c
     gcc simple-guile.o -L/usr/local/lib -lguile -lqthreads -lpthread -lm -o simple-guile
     $ ./simple-guile
     guile> (+ 1 2 3)
     6
     guile> (getpwnam "jimb")
     #("jimb" "83Z7d75W2tyJQ" 4008 10 "Jim Blandy" "/u/jimb"
       "/usr/local/bin/bash")
     guile> (exit)
     $