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| author | Edward Z. Yang <ezyang@cs.stanford.edu> | 2016-10-14 00:11:10 -0700 |
|---|---|---|
| committer | Edward Z. Yang <ezyang@cs.stanford.edu> | 2016-10-20 12:45:40 -0700 |
| commit | 9df4ce4f89b6d999822ae30ff777bdaf26665c06 (patch) | |
| tree | 03016e5127a1f3d8f74a2fe19c1aceaf7148cc4e /compiler/backpack | |
| parent | 7e77c4b2ee08d7f88df8ba47537640ec1bd70bfe (diff) | |
| download | haskell-9df4ce4f89b6d999822ae30ff777bdaf26665c06.tar.gz | |
Only delete instances when merging when there is an exact match.
Summary:
Previously, we deleted if the heads matched, which meant that
we effectively were picking an arbitrary instance if there
were incompatible instances. The new behavior makes more sense,
although without incoherent instances you are unlikely to
be able to do anything useful with the instances.
Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>
Test Plan: validate
Reviewers: austin, bgamari
Subscribers: thomie
Differential Revision: https://phabricator.haskell.org/D2596
Diffstat (limited to 'compiler/backpack')
| -rw-r--r-- | compiler/backpack/RnModIface.hs | 5 |
1 files changed, 3 insertions, 2 deletions
diff --git a/compiler/backpack/RnModIface.hs b/compiler/backpack/RnModIface.hs index 0bf7c9678f..e70254243f 100644 --- a/compiler/backpack/RnModIface.hs +++ b/compiler/backpack/RnModIface.hs @@ -319,8 +319,9 @@ rnIfaceClsInst cls_inst = do -- really matter, since we throw it out shortly after -- (for merging, we rename all of the DFuns so that they -- are unique; for instantiation, the final interface never - -- mentions DFuns since they are implicitly exported.) The - -- important thing is that it's consistent everywhere. + -- mentions DFuns since they are implicitly exported. See + -- Note [Signature merging DFuns]) The important thing is that it's + -- consistent everywhere. dfun <- rnIfaceDFun (ifDFun cls_inst) return cls_inst { ifInstCls = n , ifInstTys = tys |