And now the interpreter works (I think) correctly!

unit-tests/intepreter.sh

@@ -0,0 +1,12 @@
+#!/bin/bash
+
+expected='6'
+actual=`echo "(apply '(lambda (x y z) (/ (* y z) x)) '(2 3 4))" | target/psse 2> /dev/null | head -2 | tail -1`
+
+if [ "${expected}" = "${actual}" ]
+then
+    echo "OK"
+else
+    echo "Fail: expected '${expected}', got '${actual}'"
+    exit 1
+fi