mode failures shouldn't be silent

[jeisner]

Right now, mode failures produce nothing, not even an error message -- that's odd.

By the way, IIRC, writing foo(X) := 1 or foo(X) := X at the prompt doesn't do anything.
Why isn't that rule ok? I thought we allowed backward chaining for such rules (although we might only be able to run the query in mode +).

[timvieira]

This is a high priority fix.

[jeisner]

So shall we use the features of the git issue tracker to mark high priority issues? ("labels" or "milestones" or both)