diff options
Diffstat (limited to 'compiler/GHC/Core/InstEnv.hs')
| -rw-r--r-- | compiler/GHC/Core/InstEnv.hs | 24 |
1 files changed, 18 insertions, 6 deletions
diff --git a/compiler/GHC/Core/InstEnv.hs b/compiler/GHC/Core/InstEnv.hs index 7a4dcdc15f..92527851c5 100644 --- a/compiler/GHC/Core/InstEnv.hs +++ b/compiler/GHC/Core/InstEnv.hs @@ -7,7 +7,7 @@ The bits common to GHC.Tc.TyCl.Instance and GHC.Tc.Deriv. -} -{-# LANGUAGE DeriveDataTypeable #-} +{-# LANGUAGE DeriveDataTypeable, DeriveGeneric #-} module GHC.Core.InstEnv ( DFunId, InstMatch, ClsInstLookupResult, @@ -19,6 +19,7 @@ module GHC.Core.InstEnv ( fuzzyClsInstCmp, orphNamesOfClsInst, InstEnvs(..), VisibleOrphanModules, InstEnv, + LookupInstanceErrReason (..), mkInstEnv, emptyInstEnv, unionInstEnv, extendInstEnv, filterInstEnv, deleteFromInstEnv, deleteDFunFromInstEnv, anyInstEnv, @@ -51,6 +52,7 @@ import GHC.Types.Name import GHC.Types.Name.Set import GHC.Types.Basic import GHC.Types.Id +import GHC.Generics (Generic) import Data.Data ( Data ) import Data.List.NonEmpty ( NonEmpty (..), nonEmpty ) import qualified Data.List.NonEmpty as NE @@ -928,18 +930,28 @@ anyone noticing, so it's manifestly not ruining anyone's day.) -- yield 'Left errorMessage'. lookupUniqueInstEnv :: InstEnvs -> Class -> [Type] - -> Either SDoc (ClsInst, [Type]) + -> Either LookupInstanceErrReason (ClsInst, [Type]) lookupUniqueInstEnv instEnv cls tys = case lookupInstEnv False instEnv cls tys of ([(inst, inst_tys)], _, _) | noFlexiVar -> Right (inst, inst_tys') - | otherwise -> Left $ text "flexible type variable:" <+> - (ppr $ mkTyConApp (classTyCon cls) tys) + | otherwise -> Left $ LookupInstErrFlexiVar where inst_tys' = [ty | Just ty <- inst_tys] noFlexiVar = all isJust inst_tys - _other -> Left $ text "instance not found" <+> - (ppr $ mkTyConApp (classTyCon cls) tys) + _other -> Left $ LookupInstErrNotFound + +-- | Why a particular typeclass application couldn't be looked up. +data LookupInstanceErrReason = + -- | Tyvars aren't an exact match. + LookupInstErrNotExact + | + -- | One of the tyvars is flexible. + LookupInstErrFlexiVar + | + -- | No matching instance was found. + LookupInstErrNotFound + deriving (Generic) data Coherence = IsCoherent | IsIncoherent |