APPLY - call arbitrary function with arbitrary arguments.

Alternate Entry Name: .APPLY

Usage:

B:
   retval = apply( function_ptr, arglist_ptr, nargs );

C:
   int apply(void *function_ptr, void *arglist_ptr,
             int nargs);

Where:

function_ptr: is the address of the function you want to call.
arglist_ptr: is a pointer to a list of arguments to be passed to the function.
nargs: gives the number of arguments which are in the argument list.
retval: is the value returned by the function which "function_ptr" points to.

Description:

APPLY constructs and executes a call to the specified function. The stack is set up correctly for the number of arguments given by "nargs". The arguments in the vector pointed to by "arglist_ptr" are passed to the function and the value which the function returns is returned to "retval".

APPLY is particularly useful for routines which are called with a variable number of arguments and which wish to pass these arguments on to another function. Note that you must pass the ADDRESS of the function you wish to call; thus if you wished to call "func" the argument you would pass would be "&func".

Examples:

error( args, arg1, arg2, arg3, arg4, arg5, arg6, arg7 )
  {
    /* print out message on teletype, then exit */
    extrn printf;
    .write( -4 );
    apply( &printf, &args, nargs() );
    exit(1);
  }

Note that you must declare "printf" in an "extrn" statement. B normally recognizes function names as external because they are immediately followed by a left parenthesis "(". In a case like this where there is no parenthesis after the function name, the name must be explicitly declared as external.