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| author | Simon Peyton Jones <simonpj@microsoft.com> | 2016-10-26 10:54:16 +0100 |
|---|---|---|
| committer | Simon Peyton Jones <simonpj@microsoft.com> | 2016-10-26 11:13:18 +0100 |
| commit | 801c26372742fc79bd3756bdcb710031c716c402 (patch) | |
| tree | 5e9bdbe7d1a9bfbbe08eb4cca810a19e6e76b8c3 /compiler/typecheck/FunDeps.hs | |
| parent | a182c0e81b59494b4c8b4c03b7b9b68d81ee3381 (diff) | |
| download | haskell-801c26372742fc79bd3756bdcb710031c716c402.tar.gz | |
Fundeps work even for unary type classes
The functional-dependency improvement functions,
improveFromAnother
improveFromInstEnv
had a side-condition that said the type class has to have at
least two arguments. But not so, as Trac #12763 shows:
class C a | -> a where ...
is perfectly legal, albeit a bit of a corner case.
Diffstat (limited to 'compiler/typecheck/FunDeps.hs')
| -rw-r--r-- | compiler/typecheck/FunDeps.hs | 3 |
1 files changed, 1 insertions, 2 deletions
diff --git a/compiler/typecheck/FunDeps.hs b/compiler/typecheck/FunDeps.hs index c40be7bb13..a42f7b4922 100644 --- a/compiler/typecheck/FunDeps.hs +++ b/compiler/typecheck/FunDeps.hs @@ -166,7 +166,7 @@ improveFromAnother :: loc improveFromAnother loc pred1 pred2 | Just (cls1, tys1) <- getClassPredTys_maybe pred1 , Just (cls2, tys2) <- getClassPredTys_maybe pred2 - , tys1 `lengthAtLeast` 2 && cls1 == cls2 + , cls1 == cls2 = [ FDEqn { fd_qtvs = [], fd_eqs = eqs, fd_pred1 = pred1, fd_pred2 = pred2, fd_loc = loc } | let (cls_tvs, cls_fds) = classTvsFds cls1 , fd <- cls_fds @@ -199,7 +199,6 @@ improveFromInstEnv _inst_env _ pred = panic "improveFromInstEnv: not a class predicate" improveFromInstEnv inst_env mk_loc pred | Just (cls, tys) <- getClassPredTys_maybe pred - , tys `lengthAtLeast` 2 , let (cls_tvs, cls_fds) = classTvsFds cls instances = classInstances inst_env cls rough_tcs = roughMatchTcs tys |