Type-level infix operators

[wbukowski]

Closes #153

[wbukowski]

Should I reintroduce some of the types (e.g. Pair, Either) as operators as part of this pull request?

[Foxinio]

Should I reintroduce some of the types (e.g. Pair, Either) as operators as part of this pull request?

That's a good idea. We will immediately have some usage that will in small way test your changes.

[ppolesiuk]

Most of the changes looks good. However, there are two things that need to be fixed:

• there is no possibility of accessing type-level operator from a module, e.g. M.[+] (if this will be fixed, the TBOpID constructor should not be necessary, TVar will be sufficient)
• we agreed that allowing definitions like data A + B = ... instead of data [+] A B = ... are misleading: analogous construct on the level of expressions means something completely different (pattern matching against the constructor-level operator). This should be disallowed, at least by some warning.

[rureirureirurei]