+\subsection{TidyType}
+%* *
+%************************************************************************
+
+\begin{code}
+-- | This tidies up a type for printing in an error message, or in
+-- an interface file.
+--
+-- It doesn't change the uniques at all, just the print names.
+tidyTyVarBndr :: TidyEnv -> TyVar -> (TidyEnv, TyVar)
+tidyTyVarBndr env@(tidy_env, subst) tyvar
+ = case tidyOccName tidy_env (getOccName name) of
+ (tidy', occ') -> ((tidy', subst'), tyvar'')
+ where
+ subst' = extendVarEnv subst tyvar tyvar''
+ tyvar' = setTyVarName tyvar name'
+ name' = tidyNameOcc name occ'
+ -- Don't forget to tidy the kind for coercions!
+ tyvar'' | isCoVar tyvar = setTyVarKind tyvar' kind'
+ | otherwise = tyvar'
+ kind' = tidyType env (tyVarKind tyvar)
+ where
+ name = tyVarName tyvar
+
+---------------
+tidyFreeTyVars :: TidyEnv -> TyVarSet -> TidyEnv
+-- ^ Add the free 'TyVar's to the env in tidy form,
+-- so that we can tidy the type they are free in
+tidyFreeTyVars env tyvars = fst (tidyOpenTyVars env (varSetElems tyvars))
+
+---------------
+tidyOpenTyVars :: TidyEnv -> [TyVar] -> (TidyEnv, [TyVar])
+tidyOpenTyVars env tyvars = mapAccumL tidyOpenTyVar env tyvars
+
+---------------
+tidyOpenTyVar :: TidyEnv -> TyVar -> (TidyEnv, TyVar)
+-- ^ Treat a new 'TyVar' as a binder, and give it a fresh tidy name
+-- using the environment if one has not already been allocated. See
+-- also 'tidyTyVarBndr'
+tidyOpenTyVar env@(_, subst) tyvar
+ = case lookupVarEnv subst tyvar of
+ Just tyvar' -> (env, tyvar') -- Already substituted
+ Nothing -> tidyTyVarBndr env tyvar -- Treat it as a binder
+
+---------------
+tidyType :: TidyEnv -> Type -> Type
+tidyType env@(_, subst) ty
+ = go ty
+ where
+ go (TyVarTy tv) = case lookupVarEnv subst tv of
+ Nothing -> expand tv
+ Just tv' -> expand tv'
+ go (TyConApp tycon tys) = let args = map go tys
+ in args `seqList` TyConApp tycon args
+ go (PredTy sty) = PredTy (tidyPred env sty)
+ go (AppTy fun arg) = (AppTy $! (go fun)) $! (go arg)
+ go (FunTy fun arg) = (FunTy $! (go fun)) $! (go arg)
+ go (ForAllTy tv ty) = ForAllTy tvp $! (tidyType envp ty)
+ where
+ (envp, tvp) = tidyTyVarBndr env tv
+
+ -- Expand FlatSkols, the skolems introduced by flattening process
+ -- We don't want to show them in type error messages
+ expand tv | isTcTyVar tv
+ , FlatSkol ty <- tcTyVarDetails tv
+ = go ty
+ | otherwise
+ = TyVarTy tv
+
+---------------
+tidyTypes :: TidyEnv -> [Type] -> [Type]
+tidyTypes env tys = map (tidyType env) tys
+
+---------------
+tidyPred :: TidyEnv -> PredType -> PredType
+tidyPred env (IParam n ty) = IParam n (tidyType env ty)
+tidyPred env (ClassP clas tys) = ClassP clas (tidyTypes env tys)
+tidyPred env (EqPred ty1 ty2) = EqPred (tidyType env ty1) (tidyType env ty2)
+
+---------------
+-- | Grabs the free type variables, tidies them
+-- and then uses 'tidyType' to work over the type itself
+tidyOpenType :: TidyEnv -> Type -> (TidyEnv, Type)
+tidyOpenType env ty
+ = (env', tidyType env' ty)
+ where
+ env' = tidyFreeTyVars env (tyVarsOfType ty)
+
+---------------
+tidyOpenTypes :: TidyEnv -> [Type] -> (TidyEnv, [Type])
+tidyOpenTypes env tys = mapAccumL tidyOpenType env tys
+
+---------------
+-- | Calls 'tidyType' on a top-level type (i.e. with an empty tidying environment)
+tidyTopType :: Type -> Type
+tidyTopType ty = tidyType emptyTidyEnv ty
+
+---------------
+tidySkolemTyVar :: TidyEnv -> TcTyVar -> (TidyEnv, TcTyVar)
+-- Tidy the type inside a GenSkol, preparatory to printing it
+tidySkolemTyVar env tv
+ = ASSERT( isTcTyVar tv && (isSkolemTyVar tv || isSigTyVar tv ) )
+ (env1, mkTcTyVar (tyVarName tv) (tyVarKind tv) info1)
+ where
+ (env1, info1) = case tcTyVarDetails tv of
+ SkolemTv info -> (env1, SkolemTv info')
+ where
+ (env1, info') = tidy_skol_info env info
+ info -> (env, info)
+
+ tidy_skol_info env (GenSkol ty) = (env1, GenSkol ty1)
+ where
+ (env1, ty1) = tidyOpenType env ty
+ tidy_skol_info env info = (env, info)
+
+---------------
+tidyKind :: TidyEnv -> Kind -> (TidyEnv, Kind)
+tidyKind env k = tidyOpenType env k
+\end{code}
+
+
+%************************************************************************
+%* *