[mod3 (modulepath)]$ module purge
[mod3 (modulepath)]$ module load pgi/18.4
[mod3 (modulepath)]$ module load openmpi/3.1
[mod3 (modulepath)]$ module load foo/1.1
[mod3 (modulepath)]$ module list
Currently Loaded Modulefiles:
  1) pgi/18.4      2) openmpi/3.1   3) foo/1.1
[mod3 (modulepath)]$ foo
foo 1.1 (pgi/18.4, openmpi/3.1)
[mod3 (modulepath)]$ module switch pgi intel/2018
[mod3 (modulepath)]$ module list
Currently Loaded Modulefiles:
  1) intel/2018
  2) $MOD_GIT_ROOTDIR/doc/example/compiler-etc-dependencies/modulepath/Compiler/pgi/18.4/openmpi/3.1
  3) foo/1.1
[mod3 (modulepath)]$ foo
foo 1.1 (pgi/18.4, openmpi/3.1)
[mod3 (modulepath)]$ mpirun
mpirun (openmpi/3.1, pgi/18.4)
[mod3 (modulepath)]$ module purge
[mod3 (modulepath)]$ module load intel/2019
[mod3 (modulepath)]$ module load foo
[mod3 (modulepath)]$ module list
Currently Loaded Modulefiles:
  1) intel/2019   2) foo/2.4
[mod3 (modulepath)]$ foo
foo 2.4 (intel/2019, nompi)
[mod3 (modulepath)]$ module load openmpi
[mod3 (modulepath)]$ module list
Currently Loaded Modulefiles:
  1) intel/2019    2) foo/2.4       3) openmpi/4.0
[mod3 (modulepath)]$ foo
foo 2.4 (intel/2019, nompi)