+-- Look up the dfun of a class instance.
+--
+-- The match must be unique - ie, match exactly one instance - but the
+-- type arguments used for matching may be more specific than those of
+-- the class instance declaration. The found class instances must not have
+-- any type variables in the instance context that do not appear in the
+-- instances head (i.e., no flexi vars); for details for what this means,
+-- see the docs at InstEnv.lookupInstEnv.
+--
+lookupInst :: Class -> [Type] -> VM (DFunId, [Type])
+lookupInst cls tys
+ = do { instEnv <- getInstEnv
+ ; case lookupInstEnv instEnv cls tys of
+ ([(inst, inst_tys)], _)
+ | noFlexiVar -> return (instanceDFunId inst, inst_tys')
+ | otherwise -> pprPanic "VectMonad.lookupInst: flexi var: "
+ (ppr $ mkTyConApp (classTyCon cls) tys)
+ where
+ inst_tys' = [ty | Right ty <- inst_tys]
+ noFlexiVar = all isRight inst_tys
+ _other ->
+ pprPanic "VectMonad.lookupInst: not found: "
+ (ppr $ mkTyConApp (classTyCon cls) tys)
+ }
+ where
+ isRight (Left _) = False
+ isRight (Right _) = True
+
+-- Look up the representation tycon of a family instance.
+--
+-- The match must be unique - ie, match exactly one instance - but the
+-- type arguments used for matching may be more specific than those of
+-- the family instance declaration.
+--
+-- Return the instance tycon and its type instance. For example, if we have
+--
+-- lookupFamInst 'T' '[Int]' yields (':R42T', 'Int')
+--
+-- then we have a coercion (ie, type instance of family instance coercion)
+--
+-- :Co:R42T Int :: T [Int] ~ :R42T Int
+--
+-- which implies that :R42T was declared as 'data instance T [a]'.
+--
+lookupFamInst :: TyCon -> [Type] -> VM (TyCon, [Type])
+lookupFamInst tycon tys
+ = ASSERT( isOpenTyCon tycon )
+ do { instEnv <- getFamInstEnv
+ ; case lookupFamInstEnv instEnv tycon tys of
+ [(fam_inst, rep_tys)] -> return (famInstTyCon fam_inst, rep_tys)
+ _other ->
+ pprPanic "VectMonad.lookupFamInst: not found: "
+ (ppr $ mkTyConApp tycon tys)
+ }
+