rusty at shell functions

I'm back at the shell for scripting, without my beloved perl or even
bash. I'm having a horrible time with shell functions, so I reduced
it to this test case. What am I doing wrong? SCO 5.05

#!/bin/sh
echo "calling function foo"

foo "Dave"

foo () {
echo "$1 is not here"
return 0;
}

# ./test.sh
calling function foo
../test.sh: foo: not found


Dave
.