Wrong type being derived

[iampure@…]

In the complete small example attached there is some weird behaviour, since () gets derived in one of the cases, but there is no basic for doing so, AFAIK.

[iampure@…]

Complete example with some small remarks

[from an irc discussion]

<Heffalump> ahah, here's some interesting behaviour <Heffalump> instance Zork s (Z [Char]) Int <Heffalump> stick that in the same module as your code, and it

type checks fine.

Heffalump> stick it in a different module and import your

existing one, and looking at type of foo results in a type error

[igloo]

With the HEAD and the binding uncommented I get:

foo :: (Zork t (Z [Char]) GHC.Prim.Any) =>
       STRef t (Q t (Z [Char]) t1) -> ST t ()

Simon, can you confirm whether or not that's the expected behaviour please?

[iampure@…]

I encountered this situation today again with the code from bug #1485 in the HEAD of today.

[simonpj]

Good bug, thank you. Fixed. There was a rather subtle bug in the way 'oclose' works when generalising top-level function definitions. See Note [Important subtlety in oclose] in FunDeps for details.

Simon