diff options
| author | Simon Peyton Jones <simonpj@microsoft.com> | 2020-07-28 10:55:25 +0100 |
|---|---|---|
| committer | Marge Bot <ben+marge-bot@smart-cactus.org> | 2020-08-19 18:48:14 -0400 |
| commit | eb9bdaef6024558696e1e50b12d7fefb70483a9f (patch) | |
| tree | c6d13c6f1fb212746a627397e13308c830e9635f /compiler/GHC/Hs/Binds.hs | |
| parent | 731c8d3bc5a84515793e5dadb26adf52f9280e13 (diff) | |
| download | haskell-eb9bdaef6024558696e1e50b12d7fefb70483a9f.tar.gz | |
Add right-to-left rule for pattern bindings
Fix #18323 by adding a few lines of code to handle non-recursive
pattern bindings. see GHC.Tc.Gen.Bind
Note [Special case for non-recursive pattern bindings]
Alas, this confused the pattern-match overlap checker; see #18323.
Note that this patch only affects pattern bindings like that
for (x,y) in this program
combine :: (forall a . [a] -> a) -> [forall a. a -> a]
-> ((forall a . [a] -> a), [forall a. a -> a])
breaks = let (x,y) = combine head ids
in x y True
We need ImpredicativeTypes for those [forall a. a->a] types to be
valid. And with ImpredicativeTypes the old, unprincipled "allow
unification variables to unify with a polytype" story actually
works quite well. So this test compiles fine (if delicatedly) with
old GHCs; but not with QuickLook unless we add this patch
Diffstat (limited to 'compiler/GHC/Hs/Binds.hs')
| -rw-r--r-- | compiler/GHC/Hs/Binds.hs | 7 |
1 files changed, 1 insertions, 6 deletions
diff --git a/compiler/GHC/Hs/Binds.hs b/compiler/GHC/Hs/Binds.hs index 0933e9ba7e..327aeea2c0 100644 --- a/compiler/GHC/Hs/Binds.hs +++ b/compiler/GHC/Hs/Binds.hs @@ -317,18 +317,13 @@ data HsBindLR idL idR | XHsBindsLR !(XXHsBindsLR idL idR) -data NPatBindTc = NPatBindTc { - pat_fvs :: NameSet, -- ^ Free variables - pat_rhs_ty :: Type -- ^ Type of the GRHSs - } deriving Data - type instance XFunBind (GhcPass pL) GhcPs = NoExtField type instance XFunBind (GhcPass pL) GhcRn = NameSet -- Free variables type instance XFunBind (GhcPass pL) GhcTc = HsWrapper -- See comments on FunBind.fun_ext type instance XPatBind GhcPs (GhcPass pR) = NoExtField type instance XPatBind GhcRn (GhcPass pR) = NameSet -- Free variables -type instance XPatBind GhcTc (GhcPass pR) = NPatBindTc +type instance XPatBind GhcTc (GhcPass pR) = Type -- Type of the GRHSs type instance XVarBind (GhcPass pL) (GhcPass pR) = NoExtField type instance XAbsBinds (GhcPass pL) (GhcPass pR) = NoExtField |