splitting metavariables

Richard Eisenberg rae at cs.brynmawr.edu
Fri Oct 20 21:43:38 UTC 2017

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.


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