FN=${TMPDIR}/bashtest-$$
expect()
{
        echo expect "$@"
}

expect this is a test of proc subst
cat <(echo this is a test of proc subst)
echo this is test 2 > $FN
expect this is test 2
cat <(cat $FN)
rm -f $FN

foo=
expect a
cat ${foo:-<(echo a)}