Concrete syntax for pattern synonym type signatures

[Simon Peyton Jones]

| Instead, let me propose a slight change of shade: put the "required"
| constraints *first* and the "provided" ones *second*. Of course, we could
| leave out the required constraints.

I'm agnostic about this choice at the moment, but I don't understand your points.

| So, continuing the examples from earlier, we have
| 
| > pattern P :: forall a. Num a => forall c. (Eq a, Ord Bool, Show c) => c
| -> Bool -> T a Bool
| > pattern C :: (Eq b, Num b) => () => b -> c -> X Maybe (Maybe b)

In these examples, can you just remind us of which are match-required and which are match-provided?

| - If you write the `forall`s in, the scope builds left to right. In the
| other order, the scoping is very bizarre.

Can you be more explicit?  I don't understand.

| - I think of the "provided" bits + arguments of the constraint as what is
| matched against. The order I propose keeps these pieces together.

Can you give a concrete example?  I don't understand.

| Whatever syntax we choose, I would highly recommend putting in a helpful
| link to more information in error messages.

In principle I like this very much, but I have always stumbled on 
- writing links that will remain stable for ever (and are hence release-specific)
- keeping them up to date when the version changes
- making them easy to test e.g. in my build tree

Separate question really, but would need some systematic attention to make it work properly in general.

Simon