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(guile-tut.info)What learn1 is doing

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What learn1 is doing
--------------------

  If you compare learn1 to learn0, you will find that learn1 uses a new
Guile construct: the function `gh_new_procedure()', and its siblings:

       /* now try to define some new builtins, coded in C, so that they are
          available in Scheme. */
       gh_new_procedure1_0("c-factorial", c_factorial);
       gh_new_procedure1_0("c-sin", c_sin);
       gh_new_procedure1_0("v-t", vector_test);

  It is clear that `gh_new_procedure()' adds a new builtin routine
written in C which can be invoked from Scheme.  We can now revise our
checklist for programming with libguile, so it includes adding
callbacks.

  1. `#include <guile/gh.h>'

  2. You need to invoke the initialization routine `gh_enter()'.  This
     starts up a Scheme interpreter, handling many details.

  3. Your main() function should be almost empty: the real main program
     goes in a separate function main_prog() which is passed to
     gh_enter().  This rather arcane convention is due to the way
     Guile's garbage collector works: the whole program has to run in
     the dynamic context of `gh_enter()'.

  4. You pass strings to the Scheme interpreter with the `gh_eval_str()'
     routine.

  5. *[new]* You can now define new builtin Scheme functions; i.e.
     define new builtin Scheme functions, with the `gh_new_procedure()'
     routine.

  6. You pass strings to the Scheme interpreter with the
     `gh_eval_str()' routine.

  7. You link your program with `-lguile'.

  I breezed by the issue of how to write your C routines that are
registered to be called from Scheme.  This is non-trivial, and is
discussed at length in the `Guile Programmer's Manual'.