The following source generates a runtime error ("trying to use an int as a divert target"). It's the only time when we type parameters in the engine, so could we catch this at compile time?

(Catch: the parameter passed in might be a variable, in which case you can't catch it. But in this case where it's known to be a knot-name -- could we at least issue an appropriate warning?)

-> a (a) 

=== a (-> x) 
    -> DONE