Communication in MPI can be very complex. The aim of MPITcl is to simplify this communcation and make it friendly to the sorts of things a Tcl script might think of doing in a parallel computation. These simplifications:
Remove the concept of grouping program instances other than the world group.
Since in Tcl everything has a string representation, all data are exchanged via the MPI_CHAR data type.
The computation is logically thought of as the rank 0 script, which runs an interpreter capable of accepting commands or sourcing script files and all other ranks which just process messages.
Program instances can send scripts to other ranks in the computation.
Program instances can send Tcl data to other ranks in the computation. Program instances can establish handlers for Tcl data.
Several tag values are predefined to know how to dispatch messages received.