(use-modules (guix) (gnu))

(define code
  (plain-file "mpi.c" "
#include <assert.h>
#include <stdio.h>
#include <mpi.h>

int main (int argc, char *argv[]) {
  int err, np, rank;
  err = MPI_Init (&argc, &argv);
  assert (err == 0);
  err = MPI_Comm_size(MPI_COMM_WORLD, &np);
  assert (err == 0);
  err = MPI_Comm_rank(MPI_COMM_WORLD, &rank);
  assert (err == 0);
  printf (\"np = %i, rank = %i\\n\", np, rank);
  return 0;
} "))

(define toolchain (specification->package "gcc-toolchain"))
(define mpich (specification->package "mpich"))

(computed-file "mpi-init"
               (with-imported-modules '((guix build utils))
                 #~(begin
                     (use-modules (guix build utils))

                     (setenv "PATH"
                             (string-append #$(file-append toolchain "/bin") ":"
                                            #$(file-append mpich "/bin")))
                     (setenv "CPATH" #$(file-append mpich "/include"))
                     (setenv "LIBRARY_PATH"
                             (string-append #$(file-append mpich "/lib") ":"
                                            #$(file-append toolchain "/lib")))
                     (invoke "mpicc" "-o" #$output "-Wall" "-g"
                             #$code)

                     ;; Run the MPI code in the build environment.
                     (invoke "mpiexec" "-np" "2" #$output))))