FW: [commit: ghc] tc-arrows: Rearrange the typechecking of arrows, especially arrow "forms" (49badc9)

[Ross Paterson]

On Thu, Feb 14, 2013 at 05:40:51PM +0000, Simon Peyton-Jones wrote:
> I've pushed a new branch, tc-arrows, for the new typechecking of arrows, based on the discussion we had last week.
> 
> It all compiles, but won't work because I have done nothing to the desugaring.  
> 
> It uses our new representation with (env, nested-tuple-with-unit-at-end)
> rather than (nested-tuple-with-env-at-the-end), so desugaring needs significant attention.

I think it's done.  All but 4 of the tests pass:
- I have new versions of arrowform1 and T5283 that pass.
- The type error message for T5380 has changed.
- The gimmick used by arrowapply4 is incompatible with the new representation,
  so this test should be dropped.