Calling Lisp functions from C is sometimes possible, but is rather hackish. See funcall0 ... funcall3 in the `lisp/arch.h'. The arguments must be valid CMU CL object descriptors (e.g. fixnums must be left-shifted by 2.) See `compiler/generic/objdef.lisp' or the derived file `lisp/internals.h' for details of the object representation. `lisp/internals.h' is mechanically generated, and is not part of the source distribution. It is distributed in the `docs/' directory of the binary distribution.
Note that the garbage collector moves objects, and won't be able to fix up any
references in C variables, so either turn GC off or don't keep Lisp pointers
in C data unless they are to statically allocated objects. You can use
purify (page 
) to place live data structures in static space so that they
won't move during GC.
