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| 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/HsToCore/Expr.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/HsToCore/Expr.hs')
| -rw-r--r-- | compiler/GHC/HsToCore/Expr.hs | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/compiler/GHC/HsToCore/Expr.hs b/compiler/GHC/HsToCore/Expr.hs index 144a652484..f15434e405 100644 --- a/compiler/GHC/HsToCore/Expr.hs +++ b/compiler/GHC/HsToCore/Expr.hs @@ -212,7 +212,7 @@ dsUnliftedBind (FunBind { fun_id = L l fun ; return (bindNonRec fun rhs' body) } dsUnliftedBind (PatBind {pat_lhs = pat, pat_rhs = grhss - , pat_ext = NPatBindTc _ ty }) body + , pat_ext = ty }) body = -- let C x# y# = rhs in body -- ==> case rhs of C x# y# -> body do { match_deltas <- checkGRHSs PatBindGuards grhss |