I am hacking at the TinyScheme interpreter that is embedded in the GIMP open source image editing app.

Is this an appropriate forum to get help? or please point me to a more appropriate forum.

The idea is that whenever an unbound variable is encountered and the name exists in the GIMP API, create a foreign function object and bind it to the symbol in the global environment.

In C code of the tinyscheme interpreter, at the point the interpreter determines a symbol is unbound, more or less:

scheme_define (sc,
sc->global_env,
symbol,
sc->vptr->mk_foreign_func (sc, script_fu_marshal_procedure_call);

and then simply use the new binding as it would have been used if it was found in the first place.

Where symbol is an object of the interpreter ( type field is T_SYM and name field is "gimp-drawable-desaturate") and where script_fu_marshal_procedure_call is a foreign C function.
It seems to work, but right after the TS interpreter calls the foreign func, the symbol object is trashed: its name field is garbage. Whereas I expected it to still exist.

Probably just a stupid programming error, but is the concept sound?

Nevermind, and sorry to pollute the forum. It was my stupid programming error.

Oh, good!
So maybe I'm not the last person on the planet using TinyScheme/script-fu on GIMP.

Since you have been into the source code, I wonder if you are able to get the gimp-server working?
I did quick hack with emacs comint-mode to send the header-bytes and text, but gimp-server just hangs/dies.
[the window "Console" is painful to use... so integrating with emacs would be super nice]