splitting metavariables

[Simon Peyton Jones]

|  Actually, I wonder if we can put the check in just one spot: coreView.
|  Whenever we use coreView, we're about to inspect a type. And we should
|  never be inspecting a metavariable in this way.

Yes, that's right. Maybe that makes a useful distinction between coreView and tcView; the former should never see a meta-variable.

I'm not sure we are fully consistent on when we call each, but it'd be a good start.

Go for it

Simon

|  -----Original Message-----
|  From: Richard Eisenberg [mailto:rae at cs.brynmawr.edu]
|  Sent: 20 October 2017 22:44
|  To: Simon Peyton Jones <simonpj at microsoft.com>
|  Cc: ghc-devs <ghc-devs at haskell.org>
|  Subject: splitting metavariables
|  
|  Hi Simon,
|  
|  I just commented
|  (https://ghc.haskell.org/trac/ghc/ticket/14331#comment:35) about a
|  situation where we call splitFunTys on a type that might be a
|  metavariable. (You don't have to read the comment -- that's just to
|  set the context.) Now that I think of it, we should never call the
|  splitXXX functions on metavariables -- any time we do so is wrong. I
|  suppose it's OK if we, say, call splitTyConApp_maybe on (T alpha beta
|  gamma), because we never look through the metavariables there. But it
|  can't possible be write to call splitTyConApp_maybe on alpha.
|  
|  Do you agree? Should we ASSERT that we don't do this?
|  
|  The tcXXX variants are no different in this regard.
|  
|  Actually, I wonder if we can put the check in just one spot: coreView.
|  Whenever we use coreView, we're about to inspect a type. And we should
|  never be inspecting a metavariable in this way.
|  
|  Richard