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17.1.6 Top-level Structure of Guile-enabled Dia

Let's assume that the pre-Guile Dia code looks structurally like this:

• main ()
  • do lots of initialization and setup stuff
  • enter Gtk main loop

When you add Guile to a program, one (rather technical) requirement is that Guile's garbage collector needs to know where the bottom of the C stack is. The easiest way to ensure this is to use scm_boot_guile like this:

• main ()
  • do lots of initialization and setup stuff
  • scm_boot_guile (argc, argv, inner_main, NULL)
• inner_main ()
  • define all SMOB types
  • export primitives to Scheme using scm_c_define_gsubr
  • enter Gtk main loop

In other words, you move the guts of what was previously in your main function into a new function called inner_main, and then add a scm_boot_guile call, with inner_main as a parameter, to the end of main.

Assuming that you are using SMOBs and have written primitive code as described in the preceding subsections, you also need to insert calls to declare your new SMOBs and export the primitives to Scheme. These declarations must happen inside the dynamic scope of the scm_boot_guile call, but also before any code is run that could possibly use them -- the beginning of inner_main is an ideal place for this.