1. double
        1. char*
        1. Tcl_Obj*
        1. void*
    1. `<returnType>` is the return type for the C function
      1. The supported types are:
        1. void: No return value
        1. ok: Return TCL_OK or TCL_ERROR
        1. ok: Return TCL\_OK or TCL_ERROR
        1. int
        1. long
        1. float
        1. double
        1. char*: TCL_STATIC string (immutable from C)
        1. string, dstring: TCL_DYNAMIC string (mutable from C)
        1. vstring: TCL_VOLATILE string (mutable from C)