This is a guile interpreter with an extension that allows manipulating
process   groups   (MPI   communicators)   and   basic   inter-process
communication. To build it execute

    cd guile
    make

Then start the custom interpreter:

    $ export GUILE_LOAD_PATH=..
    $ ./guile-comm

Try importing the comm module --- this initializes the module defining
basic communication primitives:

    > (use-modules (guile comm))

The comm-init procedure returns  the MPI_COMM_WORLD communicator as an
integer:

    > (comm-init (command-line))
    $1 = 0

Compute  Pi with  that communicator  by adding  that many  terms (this
needs a few seconds of your patience):

    > (comm-pi 0 100000000)
    $2 = 3.14159265359023

Finalize MPI:

    > (comm-finalize)
    $3 = 0

MPI does not handle STDIN multiplexing so for parallel runs execute it
in batch mode:

    $ export GUILE_LOAD_PATH=..
    $ mpirun -np 4 $PWD/guile-comm -s $PWD/test-guile-comm.scm

Here  $PWD might  be necessary  if mpirun  does not  respect  CWD when
spawning processes.