Node:A Sample Guile Main Program, Previous:Guile Initialization Functions, Up:Linking Programs With Guile

5.3.2 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 as this file as template to generate a configure script. In order for Autoconf to find the GUILE_FLAGS macro, you will need to run aclocal first. This is not really Guile specific, so you should refer to the Autoconf documentation REFFIXME when in doubt.

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)
$