Question

I use TCL 8.4 and for that version I need to add a new mathematical function into TCL interpreter by using TCL library function, particularly Tcl_CreateMathFunc. But I could not find a single example of how it can be done. Please could you write for me a very simple example, assuming that in the C code you have a Tcl_Interp *interp to which you should add a math function (say, a function that multiplies two double numbers).

Answer 1

I once did some alternative implementations of random number generators for Tcl and you can look at some examples at the git repository. The files in generic implement both a tcl command and a tcl math function for each PRNG.

So for instance in the Mersenne Twister implementation, in the package init function we add the new function to the interpreter by declaring

Tcl_CreateMathFunc(interp, "mt_rand", 1, (Tcl_ValueType *)NULL, RandProc, (ClientData)state);

this registers the C function RandProc for us. In this case the function takes no arguments but the seeding equivalent (srand) shows how to handle a single parameter.

/*
 * A Tcl math function that implements rand() using the Mersenne Twister
 * Pseudo-random number generator.
 */
 static int
 RandProc(ClientData clientData, Tcl_Interp *interp, Tcl_Value *args, Tcl_Value *resultPtr)
 {
     State * state = (State *)clientData;
     if (! (state->flags & Initialized)) {
         unsigned long seed;
         /* This is based upon the standard Tcl rand() initializer */
         seed = time(NULL) + ((long)Tcl_GetCurrentThread()<<12);
         InitState(state, seed);
     }
     resultPtr->type = TCL_DOUBLE;
     resultPtr->doubleValue = RandomDouble(state);
     return TCL_OK;
 }