Implicit Functions Fail

[corlin-fardal]

When trying to make implicit functions in the implicit parameters playground, things like "?f ?x", "?f 0", or even "let f = ?g in f ?x" fail, stating that the left hand side is not a function.

[tpetricek]

This looks like a bug - there is no reason in principle why this should not be allowed - that said, I don't think I'll be able to do any more work on this project, so it'll likely stay the way it is - unless someone curious sends a PR with a fix :)