5.2.2 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 pkg-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=`pkg-config --cflags guile-2.0`
     
     # Tell the linker what libraries to use and where to find them.
     LIBS=`pkg-config --libs guile-2.0`
     
     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. Here is a configure.ac file for simple-guile that uses the standard PKG_CHECK_MODULES macro to check for Guile. Autoconf will process this file into a configure script. We recommend invoking Autoconf via the autoreconf utility.

     AC_INIT(simple-guile.c)
     
     # Find a C compiler.
     AC_PROG_CC
     
     # Check for Guile
     PKG_CHECK_MODULES([GUILE], [guile-2.0])
     
     # Generate a Makefile, based on the results.
     AC_OUTPUT(Makefile)

Run autoreconf -vif to generate configure.

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_LIBS@
     
     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.ac template, and distribute configure with the application. Here's how a user might go about building the application:

     $ ls
     Makefile.in     configure*      configure.ac    simple-guile.c
     $ ./configure
     checking for gcc... ccache gcc
     checking whether the C compiler works... yes
     checking for C compiler default output file name... a.out
     checking for suffix of executables...
     checking whether we are cross compiling... no
     checking for suffix of object files... o
     checking whether we are using the GNU C compiler... yes
     checking whether ccache gcc accepts -g... yes
     checking for ccache gcc option to accept ISO C89... none needed
     checking for pkg-config... /usr/bin/pkg-config
     checking pkg-config is at least version 0.9.0... yes
     checking for GUILE... yes
     configure: creating ./config.status
     config.status: creating Makefile
     $ make
     [...]
     $ ./simple-guile
     guile> (+ 1 2 3)
     6
     guile> (getpwnam "jimb")
     #("jimb" "83Z7d75W2tyJQ" 4008 10 "Jim Blandy" "/u/jimb"
       "/usr/local/bin/bash")
     guile> (exit)
     $