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Guile Reference Manual

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19.4 Starting and controlling the interpreter

In almost every case, your first gh_ call will be:

Function: void gh_enter (int argc, char *argv[], void (*main_prog)())
Starts up a Scheme interpreter with all the builtin Scheme primitives. gh_enter() never exits, and the user's code should all be in the main_prog() function. argc and argv will be passed to main_prog.

Function: void main_prog (int argc, char *argv[])
This is the user's main program. It will be invoked by gh_enter() after Guile has been started up.

Note that you can use gh_repl inside gh_enter (in other words, inside the code for main-prog) if you want the program to be controlled by a Scheme read-eval-print loop.

A convenience routine which enters the Guile interpreter with the standard Guile read-eval-print loop (REPL) is:

Function: void gh_repl (int argc, char *argv[])
Enters the Scheme interpreter giving control to the Scheme REPL. Arguments are processed as if the Guile program `guile' were being invoked.

Note that gh_repl should be used inside gh_enter, since any Guile interpreter calls are meaningless unless they happen in the context of the interpreter.

Also note that when you use gh_repl, your program will be controlled by Guile's REPL (which is written in Scheme and has many useful features). Use straight C code inside gh_enter if you want to maintain execution control in your C program.

You will typically use gh_enter and gh_repl when you want a Guile interpreter enhanced by your own libraries, but otherwise quite normal. For example, to build a Guile--derived program that includes some random number routines GSL (GNU Scientific Library), you would write a C program that looks like this:

 
#include <guile/gh.h>
#include <gsl_ran.h>

/* random number suite */
SCM gw_ran_seed(SCM s)
{
  gsl_ran_seed(gh_scm2int(s));
  return SCM_UNSPECIFIED;
}

SCM gw_ran_random()
{
  SCM x;

  x = gh_ulong2scm(gsl_ran_random());
  return x;
}

SCM gw_ran_uniform()
{
  SCM x;

  x = gh_double2scm(gsl_ran_uniform());
  return x;
}
SCM gw_ran_max()
{
  return gh_double2scm(gsl_ran_max());
}

void
init_gsl()
{
  /* random number suite */
  gh_new_procedure("gsl-ran-seed", gw_ran_seed, 1, 0, 0);
  gh_new_procedure("gsl-ran-random", gw_ran_random, 0, 0, 0);
  gh_new_procedure("gsl-ran-uniform", gw_ran_uniform, 0, 0, 0);
  gh_new_procedure("gsl-ran-max", gw_ran_max, 0, 0, 0);
}

void
main_prog (int argc, char *argv[])
{
  init_gsl();

  gh_repl(argc, argv);
}

int
main (int argc, char *argv[])
{
  gh_enter (argc, argv, main_prog);
}

Then, supposing the C program is in `guile-gsl.c', you could compile it with gcc -o guile-gsl guile-gsl.c -lguile -lgsl.

The resulting program `guile-gsl' would have new primitive procedures gsl-ran-random, gsl-ran-gaussian and so forth.


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