<%def name="callee(value_from_caller)"> I am callee, called with value ${value_from_caller}. I'll send the incremented value back to the caller! The body of the caller will be: ${caller.body(value_from_callee=value_from_caller+1)} <%call expr="callee(42)" args="value_from_callee"> I am the caller. I have been called back by the callee with the value ${value_from_callee}.