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| author | Simon Peyton Jones <simonpj@microsoft.com> | 2016-11-04 10:43:36 +0000 |
|---|---|---|
| committer | Simon Peyton Jones <simonpj@microsoft.com> | 2016-11-04 12:32:31 +0000 |
| commit | 2cdd9bd5208e3ad78d7a3b8b82c8ae1be486b34d (patch) | |
| tree | 0bccf87de19aa17d7675630f55ada70eab765493 /compiler/prelude | |
| parent | 7b0ae417026c587dbc9697f678d560b1dc975d50 (diff) | |
| download | haskell-2cdd9bd5208e3ad78d7a3b8b82c8ae1be486b34d.tar.gz | |
Take account of injectivity when doing fundeps
This fixes Trac #12803. Yikes!
See Note [Care with type functions].
Diffstat (limited to 'compiler/prelude')
| -rw-r--r-- | compiler/prelude/TysWiredIn.hs | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/compiler/prelude/TysWiredIn.hs b/compiler/prelude/TysWiredIn.hs index 7f4d072bfd..d3ba85e6e3 100644 --- a/compiler/prelude/TysWiredIn.hs +++ b/compiler/prelude/TysWiredIn.hs @@ -991,6 +991,11 @@ mk_sum arity = (tycon, sum_cons) -- See Note [The equality types story] in TysPrim -- (:~~: :: forall k1 k2 (a :: k1) (b :: k2). a -> b -> Constraint) +-- +-- It's tempting to put functional dependencies on (~~), but it's not +-- necessary because the functional-dependency coverage check looks +-- through superclasses, and (~#) is handled in that check. + heqTyCon, coercibleTyCon :: TyCon heqClass, coercibleClass :: Class heqDataCon, coercibleDataCon :: DataCon |