+%
+% (c) The GRASP/AQUA Project, Glasgow University, 1998
+%
+\section[Type]{Type - public interface}
+
\begin{code}
module Type (
- Type(..), TyNote(..), -- Representation visible to friends
- Kind, TyVarSubst,
-
- superKind, superBoxity, -- :: SuperKind
-
- boxedKind, -- :: Kind :: BX
- anyBoxKind, -- :: Kind :: BX
- typeCon, -- :: KindCon :: BX -> KX
- anyBoxCon, -- :: KindCon :: BX
+ -- re-exports from TypeRep
+ TyThing(..), Type, PredType(..), ThetaType,
+ funTyCon,
- boxedTypeKind, unboxedTypeKind, openTypeKind, -- Kind :: superKind
+ -- Re-exports from Kind
+ module Kind,
- mkArrowKind, mkArrowKinds, hasMoreBoxityInfo,
-
- funTyCon,
+ -- Re-exports from TyCon
+ PrimRep(..),
mkTyVarTy, mkTyVarTys, getTyVar, getTyVar_maybe, isTyVarTy,
mkAppTy, mkAppTys, splitAppTy, splitAppTys, splitAppTy_maybe,
- mkFunTy, mkFunTys, splitFunTy_maybe, splitFunTys, funResultTy,
- zipFunTys,
+ mkFunTy, mkFunTys, splitFunTy, splitFunTy_maybe,
+ splitFunTys, splitFunTysN,
+ funResultTy, funArgTy, zipFunTys, isFunTy,
+
+ mkGenTyConApp, mkTyConApp, mkTyConTy,
+ tyConAppTyCon, tyConAppArgs,
+ splitTyConApp_maybe, splitTyConApp,
- mkTyConApp, mkTyConTy, splitTyConApp_maybe,
- splitAlgTyConApp_maybe, splitAlgTyConApp,
- mkDictTy, splitDictTy_maybe, isDictTy,
+ mkSynTy,
- mkSynTy, isSynTy, deNoteType,
+ repType, typePrimRep, coreView, deepCoreView,
mkForAllTy, mkForAllTys, splitForAllTy_maybe, splitForAllTys,
- applyTy, applyTys, isForAllTy,
- mkPiType,
+ applyTy, applyTys, isForAllTy, dropForAlls,
- TauType, RhoType, SigmaType, ThetaType,
- isTauTy,
- mkRhoTy, splitRhoTy,
- mkSigmaTy, splitSigmaTy,
+ -- Source types
+ predTypeRep, mkPredTy, mkPredTys,
+
+ -- Newtypes
+ splitRecNewType_maybe,
-- Lifting and boxity
- isUnLiftedType, isUnboxedType, isUnboxedTupleType, isAlgType, isDataType,
- typePrimRep,
+ isUnLiftedType, isUnboxedTupleType, isAlgType, isPrimitiveType,
+ isStrictType, isStrictPred,
-- Free variables
- tyVarsOfType, tyVarsOfTypes, namesOfType, typeKind,
- addFreeTyVars,
-
- -- Substitution
- substTy, substTheta, fullSubstTy, substTyVar,
- substTopTy, substTopTheta,
+ tyVarsOfType, tyVarsOfTypes, tyVarsOfPred, tyVarsOfTheta,
+ typeKind, addFreeTyVars,
-- Tidying up for printing
- tidyType, tidyTypes,
- tidyOpenType, tidyOpenTypes,
- tidyTyVar, tidyTyVars,
- tidyTopType
+ tidyType, tidyTypes,
+ tidyOpenType, tidyOpenTypes,
+ tidyTyVarBndr, tidyFreeTyVars,
+ tidyOpenTyVar, tidyOpenTyVars,
+ tidyTopType, tidyPred,
+
+ -- Comparison
+ coreEqType, tcEqType, tcEqTypes, tcCmpType, tcCmpTypes,
+ tcEqPred, tcCmpPred, tcEqTypeX,
+
+ -- Seq
+ seqType, seqTypes,
+
+ -- Type substitutions
+ TvSubst(..), -- Representation visible to a few friends
+ TvSubstEnv, emptyTvSubst,
+ mkTvSubst, zipTvSubst, zipTopTvSubst, mkTopTvSubst,
+ getTvSubstEnv, setTvSubstEnv, getTvInScope, extendTvInScope,
+ extendTvSubst, extendTvSubstList, isInScope, composeTvSubst,
+
+ -- Performing substitution on types
+ substTy, substTys, substTyWith, substTheta, substTyVar, substTyVarBndr,
+ deShadowTy,
+
+ -- Pretty-printing
+ pprType, pprParendType, pprTyThingCategory,
+ pprPred, pprTheta, pprThetaArrow, pprClassPred
) where
#include "HsVersions.h"
-import {-# SOURCE #-} DataCon( DataCon )
-import {-# SOURCE #-} PprType( pprType ) -- Only called in debug messages
+-- We import the representation and primitive functions from TypeRep.
+-- Many things are reexported, but not the representation!
+
+import TypeRep
-- friends:
-import Var ( Id, TyVar, IdOrTyVar,
- tyVarKind, tyVarName, isId, idType, setTyVarName
- )
+import Kind
+import Var ( Var, TyVar, tyVarKind, tyVarName, setTyVarName )
import VarEnv
import VarSet
-import Name ( NamedThing(..), Provenance(..), ExportFlag(..),
- mkWiredInTyConName, mkGlobalName, mkLocalName, mkKindOccFS, tcName,
- tidyOccName, TidyOccEnv
- )
-import NameSet
-import Class ( classTyCon, Class )
-import TyCon ( TyCon, KindCon,
- mkFunTyCon, mkKindCon, mkSuperKindCon,
- matchesTyCon, isUnboxedTupleTyCon, isUnLiftedTyCon,
- isFunTyCon, isDataTyCon,
- isAlgTyCon, isSynTyCon, tyConArity,
- tyConKind, tyConDataCons, getSynTyConDefn,
- tyConPrimRep, tyConClass_maybe
+import Name ( NamedThing(..), mkInternalName, tidyOccName )
+import Class ( Class, classTyCon )
+import TyCon ( TyCon, isRecursiveTyCon, isPrimTyCon,
+ isUnboxedTupleTyCon, isUnLiftedTyCon,
+ isFunTyCon, isNewTyCon, newTyConRep, newTyConRhs,
+ isAlgTyCon, isSynTyCon, tyConArity, newTyConRhs_maybe,
+ tyConKind, getSynTyConDefn, PrimRep(..), tyConPrimRep,
)
-- others
-import BasicTypes ( Unused )
-import SrcLoc ( mkBuiltinSrcLoc, noSrcLoc )
-import PrelMods ( pREL_GHC )
-import Maybes ( maybeToBool )
-import PrimRep ( PrimRep(..), isFollowableRep )
-import Unique -- quite a few *Keys
-import Util ( thenCmp, mapAccumL, seqList, ($!) )
+import CmdLineOpts ( opt_DictsStrict )
+import SrcLoc ( noSrcLoc )
+import Unique ( Uniquable(..) )
+import Util ( mapAccumL, seqList, lengthIs, snocView, thenCmp, isEqual )
import Outputable
-
+import UniqSet ( sizeUniqSet ) -- Should come via VarSet
+import Maybe ( isJust )
\end{code}
-%************************************************************************
-%* *
-\subsection{Type Classifications}
-%* *
-%************************************************************************
-
-A type is
-
- *unboxed* iff its representation is other than a pointer
- Unboxed types cannot instantiate a type variable.
- Unboxed types are always unlifted.
-
- *lifted* A type is lifted iff it has bottom as an element.
- Closures always have lifted types: i.e. any
- let-bound identifier in Core must have a lifted
- type. Operationally, a lifted object is one that
- can be entered.
- (NOTE: previously "pointed").
-
- *algebraic* A type with one or more constructors, whether declared
- with "data" or "newtype".
- An algebraic type is one that can be deconstructed
- with a case expression.
-
- *NOT* the same as lifted types, because we also
- include unboxed tuples in this classification.
-
- *data* A type declared with "data". Also boxed tuples.
-
- *primitive* iff it is a built-in type that can't be expressed
- in Haskell.
-
-Currently, all primitive types are unlifted, but that's not necessarily
-the case. (E.g. Int could be primitive.)
-
-Some primitive types are unboxed, such as Int#, whereas some are boxed
-but unlifted (such as ByteArray#). The only primitive types that we
-classify as algebraic are the unboxed tuples.
-
-examples of type classifications:
-
-Type primitive boxed lifted algebraic
------------------------------------------------------------------------------
-Int#, Yes No No No
-ByteArray# Yes Yes No No
-(# a, b #) Yes No No Yes
-( a, b ) No Yes Yes Yes
-[a] No Yes Yes Yes
%************************************************************************
%* *
-\subsection{The data type}
+ Type representation
%* *
%************************************************************************
+In Core, we "look through" non-recursive newtypes and PredTypes.
\begin{code}
-type SuperKind = Type
-type Kind = Type
-
-type TyVarSubst = TyVarEnv Type
-
-data Type
- = TyVarTy TyVar
-
- | AppTy
- Type -- Function is *not* a TyConApp
- Type
-
- | TyConApp -- Application of a TyCon
- TyCon -- *Invariant* saturated appliations of FunTyCon and
- -- synonyms have their own constructors, below.
- [Type] -- Might not be saturated.
-
- | FunTy -- Special case of TyConApp: TyConApp FunTyCon [t1,t2]
- Type
- Type
-
- | NoteTy -- Saturated application of a type synonym
- TyNote
- Type -- The expanded version
-
- | ForAllTy
- TyVar
- Type -- TypeKind
-
-data TyNote
- = SynNote Type -- The unexpanded version of the type synonym; always a TyConApp
- | FTVNote TyVarSet -- The free type variables of the noted expression
+{-# INLINE coreView #-}
+coreView :: Type -> Maybe Type
+-- Srips off the *top layer only* of a type to give
+-- its underlying representation type.
+-- Returns Nothing if there is nothing to look through.
+--
+-- By being non-recursive and inlined, this case analysis gets efficiently
+-- joined onto the case analysis that the caller is already doing
+coreView (NoteTy _ ty) = Just ty
+coreView (PredTy p) = Just (predTypeRep p)
+coreView (TyConApp tc tys) = expandNewTcApp tc tys
+coreView ty = Nothing
+
+deepCoreView :: Type -> Type
+-- Apply coreView recursively
+deepCoreView ty
+ | Just ty' <- coreView ty = deepCoreView ty'
+deepCoreView (TyVarTy tv) = TyVarTy tv
+deepCoreView (TyConApp tc tys) = TyConApp tc (map deepCoreView tys)
+deepCoreView (AppTy t1 t2) = AppTy (deepCoreView t1) (deepCoreView t2)
+deepCoreView (FunTy t1 t2) = FunTy (deepCoreView t1) (deepCoreView t2)
+deepCoreView (ForAllTy tv ty) = ForAllTy tv (deepCoreView ty)
+ -- No NoteTy, no PredTy
+
+expandNewTcApp :: TyCon -> [Type] -> Maybe Type
+-- A local helper function (not exported)
+-- Expands *the outermoset level of* a newtype application to
+-- *either* a vanilla TyConApp (recursive newtype, or non-saturated)
+-- *or* the newtype representation (otherwise), meaning the
+-- type written in the RHS of the newtype decl,
+-- which may itself be a newtype
+--
+-- Example: newtype R = MkR S
+-- newtype S = MkS T
+-- newtype T = MkT (T -> T)
+-- expandNewTcApp on R gives Just S
+-- on S gives Just T
+-- on T gives Nothing (no expansion)
+
+expandNewTcApp tc tys = case newTyConRhs_maybe tc tys of
+ Nothing -> Nothing
+ Just (tenv, rhs) -> Just (substTy (mkTopTvSubst tenv) rhs)
\end{code}
%************************************************************************
%* *
-\subsection{Kinds}
-%* *
-%************************************************************************
-
-Kinds
-~~~~~
-k::K = Type bx
- | k -> k
- | kv
-
-kv :: KX is a kind variable
-
-Type :: BX -> KX
-
-bx::BX = Boxed
- | Unboxed
- | AnyBox -- Used *only* for special built-in things
- -- like error :: forall (a::*?). String -> a
- -- Here, the 'a' can be instantiated to a boxed or
- -- unboxed type.
- | bv
-
-bxv :: BX is a boxity variable
-
-sk = KX -- A kind
- | BX -- A boxity
- | sk -> sk -- In ptic (BX -> KX)
-
-\begin{code}
-mk_kind_name key str = mkGlobalName key pREL_GHC (mkKindOccFS tcName str)
- (LocalDef mkBuiltinSrcLoc NotExported)
- -- mk_kind_name is a bit of a hack
- -- The LocalDef means that we print the name without
- -- a qualifier, which is what we want for these kinds.
- -- It's used for both Kinds and Boxities
-\end{code}
-
-Define KX, BX.
-
-\begin{code}
-superKind :: SuperKind -- KX, the type of all kinds
-superKindName = mk_kind_name kindConKey SLIT("KX")
-superKind = TyConApp (mkSuperKindCon superKindName) []
-
-superBoxity :: SuperKind -- BX, the type of all boxities
-superBoxityName = mk_kind_name boxityConKey SLIT("BX")
-superBoxity = TyConApp (mkSuperKindCon superBoxityName) []
-\end{code}
-
-Define Boxed, Unboxed, AnyBox
-
-\begin{code}
-boxedKind, unboxedKind, anyBoxKind :: Kind -- Of superkind superBoxity
-
-boxedConName = mk_kind_name boxedConKey SLIT("*")
-boxedKind = TyConApp (mkKindCon boxedConName superBoxity) []
-
-unboxedConName = mk_kind_name unboxedConKey SLIT("#")
-unboxedKind = TyConApp (mkKindCon unboxedConName superBoxity) []
-
-anyBoxConName = mk_kind_name anyBoxConKey SLIT("?")
-anyBoxCon = mkKindCon anyBoxConName superBoxity -- A kind of wild card
-anyBoxKind = TyConApp anyBoxCon []
-\end{code}
-
-Define Type
-
-\begin{code}
-typeCon :: KindCon
-typeConName = mk_kind_name typeConKey SLIT("Type")
-typeCon = mkKindCon typeConName (superBoxity `FunTy` superKind)
-\end{code}
-
-Define (Type Boxed), (Type Unboxed), (Type AnyBox)
-
-\begin{code}
-boxedTypeKind, unboxedTypeKind, openTypeKind :: Kind
-boxedTypeKind = TyConApp typeCon [boxedKind]
-unboxedTypeKind = TyConApp typeCon [unboxedKind]
-openTypeKind = TyConApp typeCon [anyBoxKind]
-
-mkArrowKind :: Kind -> Kind -> Kind
-mkArrowKind k1 k2 = k1 `FunTy` k2
-
-mkArrowKinds :: [Kind] -> Kind -> Kind
-mkArrowKinds arg_kinds result_kind = foldr mkArrowKind result_kind arg_kinds
-\end{code}
-
-\begin{code}
-hasMoreBoxityInfo :: Kind -> Kind -> Bool
-hasMoreBoxityInfo k1 k2
- | k2 == openTypeKind = ASSERT( is_type_kind k1) True
- | otherwise = k1 == k2
- where
- -- Returns true for things of form (Type x)
- is_type_kind k = case splitTyConApp_maybe k of
- Just (tc,[_]) -> tc == typeCon
- Nothing -> False
-\end{code}
-
-
-%************************************************************************
-%* *
-\subsection{Wired-in type constructors
-%* *
-%************************************************************************
-
-We define a few wired-in type constructors here to avoid module knots
-
-\begin{code}
-funTyConName = mkWiredInTyConName funTyConKey pREL_GHC SLIT("(->)") funTyCon
-funTyCon = mkFunTyCon funTyConName (mkArrowKinds [boxedTypeKind, boxedTypeKind] boxedTypeKind)
-\end{code}
-
-
-
-%************************************************************************
-%* *
\subsection{Constructor-specific functions}
%* *
%************************************************************************
mkTyVarTys = map mkTyVarTy -- a common use of mkTyVarTy
getTyVar :: String -> Type -> TyVar
-getTyVar msg (TyVarTy tv) = tv
-getTyVar msg (NoteTy _ t) = getTyVar msg t
-getTyVar msg other = panic ("getTyVar: " ++ msg)
-
-getTyVar_maybe :: Type -> Maybe TyVar
-getTyVar_maybe (TyVarTy tv) = Just tv
-getTyVar_maybe (NoteTy _ t) = getTyVar_maybe t
-getTyVar_maybe other = Nothing
+getTyVar msg ty = case getTyVar_maybe ty of
+ Just tv -> tv
+ Nothing -> panic ("getTyVar: " ++ msg)
isTyVarTy :: Type -> Bool
-isTyVarTy (TyVarTy tv) = True
-isTyVarTy (NoteTy _ ty) = isTyVarTy ty
-isTyVarTy other = False
+isTyVarTy ty = isJust (getTyVar_maybe ty)
+
+getTyVar_maybe :: Type -> Maybe TyVar
+getTyVar_maybe ty | Just ty' <- coreView ty = getTyVar_maybe ty'
+getTyVar_maybe (TyVarTy tv) = Just tv
+getTyVar_maybe other = Nothing
\end{code}
invariant: use it.
\begin{code}
-mkAppTy orig_ty1 orig_ty2 = mk_app orig_ty1
+mkAppTy orig_ty1 orig_ty2
+ = mk_app orig_ty1
where
mk_app (NoteTy _ ty1) = mk_app ty1
- mk_app (TyConApp tc tys) = mkTyConApp tc (tys ++ [orig_ty2])
+ mk_app (TyConApp tc tys) = mkGenTyConApp tc (tys ++ [orig_ty2])
mk_app ty1 = AppTy orig_ty1 orig_ty2
+ -- We call mkGenTyConApp because the TyConApp could be an
+ -- under-saturated type synonym. GHC allows that; e.g.
+ -- type Foo k = k a -> k a
+ -- type Id x = x
+ -- foo :: Foo Id -> Foo Id
+ --
+ -- Here Id is partially applied in the type sig for Foo,
+ -- but once the type synonyms are expanded all is well
mkAppTys :: Type -> [Type] -> Type
mkAppTys orig_ty1 [] = orig_ty1
-- This check for an empty list of type arguments
- -- avoids the needless of a type synonym constructor.
+ -- avoids the needless loss of a type synonym constructor.
-- For example: mkAppTys Rational []
-- returns to (Ratio Integer), which has needlessly lost
-- the Rational part.
-mkAppTys orig_ty1 orig_tys2 = mk_app orig_ty1
+mkAppTys orig_ty1 orig_tys2
+ = mk_app orig_ty1
where
mk_app (NoteTy _ ty1) = mk_app ty1
- mk_app (TyConApp tc tys) = mkTyConApp tc (tys ++ orig_tys2)
+ mk_app (TyConApp tc tys) = mkGenTyConApp tc (tys ++ orig_tys2)
+ -- mkGenTyConApp: see notes with mkAppTy
mk_app ty1 = foldl AppTy orig_ty1 orig_tys2
splitAppTy_maybe :: Type -> Maybe (Type, Type)
+splitAppTy_maybe ty | Just ty' <- coreView ty = splitAppTy_maybe ty'
splitAppTy_maybe (FunTy ty1 ty2) = Just (TyConApp funTyCon [ty1], ty2)
splitAppTy_maybe (AppTy ty1 ty2) = Just (ty1, ty2)
-splitAppTy_maybe (NoteTy _ ty) = splitAppTy_maybe ty
-splitAppTy_maybe (TyConApp tc []) = Nothing
-splitAppTy_maybe (TyConApp tc tys) = split tys []
- where
- split [ty2] acc = Just (TyConApp tc (reverse acc), ty2)
- split (ty:tys) acc = split tys (ty:acc)
-
-splitAppTy_maybe other = Nothing
+splitAppTy_maybe (TyConApp tc tys) = case snocView tys of
+ Nothing -> Nothing
+ Just (tys',ty') -> Just (TyConApp tc tys', ty')
+splitAppTy_maybe other = Nothing
splitAppTy :: Type -> (Type, Type)
splitAppTy ty = case splitAppTy_maybe ty of
splitAppTys :: Type -> (Type, [Type])
splitAppTys ty = split ty ty []
where
+ split orig_ty ty args | Just ty' <- coreView ty = split orig_ty ty' args
split orig_ty (AppTy ty arg) args = split ty ty (arg:args)
- split orig_ty (NoteTy _ ty) args = split orig_ty ty args
+ split orig_ty (TyConApp tc tc_args) args = (TyConApp tc [], tc_args ++ args)
split orig_ty (FunTy ty1 ty2) args = ASSERT( null args )
(TyConApp funTyCon [], [ty1,ty2])
- split orig_ty (TyConApp tc tc_args) args = (TyConApp tc [], tc_args ++ args)
split orig_ty ty args = (orig_ty, args)
\end{code}
mkFunTys :: [Type] -> Type -> Type
mkFunTys tys ty = foldr FunTy ty tys
-splitFunTy_maybe :: Type -> Maybe (Type, Type)
-splitFunTy_maybe (FunTy arg res) = Just (arg, res)
-splitFunTy_maybe (NoteTy _ ty) = splitFunTy_maybe ty
-splitFunTy_maybe other = Nothing
+isFunTy :: Type -> Bool
+isFunTy ty = isJust (splitFunTy_maybe ty)
+splitFunTy :: Type -> (Type, Type)
+splitFunTy ty | Just ty' <- coreView ty = splitFunTy ty'
+splitFunTy (FunTy arg res) = (arg, res)
+splitFunTy other = pprPanic "splitFunTy" (ppr other)
+
+splitFunTy_maybe :: Type -> Maybe (Type, Type)
+splitFunTy_maybe ty | Just ty' <- coreView ty = splitFunTy_maybe ty'
+splitFunTy_maybe (FunTy arg res) = Just (arg, res)
+splitFunTy_maybe other = Nothing
splitFunTys :: Type -> ([Type], Type)
splitFunTys ty = split [] ty ty
where
- split args orig_ty (FunTy arg res) = split (arg:args) res res
- split args orig_ty (NoteTy _ ty) = split args orig_ty ty
- split args orig_ty ty = (reverse args, orig_ty)
+ split args orig_ty ty | Just ty' <- coreView ty = split args orig_ty ty'
+ split args orig_ty (FunTy arg res) = split (arg:args) res res
+ split args orig_ty ty = (reverse args, orig_ty)
+
+splitFunTysN :: Int -> Type -> ([Type], Type)
+-- Split off exactly n arg tys
+splitFunTysN 0 ty = ([], ty)
+splitFunTysN n ty = case splitFunTy ty of { (arg, res) ->
+ case splitFunTysN (n-1) res of { (args, res) ->
+ (arg:args, res) }}
zipFunTys :: Outputable a => [a] -> Type -> ([(a,Type)], Type)
zipFunTys orig_xs orig_ty = split [] orig_xs orig_ty orig_ty
where
- split acc [] nty ty = (reverse acc, nty)
- split acc (x:xs) nty (FunTy arg res) = split ((x,arg):acc) xs res res
- split acc xs nty (NoteTy _ ty) = split acc xs nty ty
- split acc (x:xs) nty ty = pprPanic "zipFunTys" (ppr orig_xs <+> pprType orig_ty)
+ split acc [] nty ty = (reverse acc, nty)
+ split acc xs nty ty
+ | Just ty' <- coreView ty = split acc xs nty ty'
+ split acc (x:xs) nty (FunTy arg res) = split ((x,arg):acc) xs res res
+ split acc (x:xs) nty ty = pprPanic "zipFunTys" (ppr orig_xs <+> ppr orig_ty)
funResultTy :: Type -> Type
-funResultTy (FunTy arg res) = res
-funResultTy (NoteTy _ ty) = funResultTy ty
-funResultTy ty = pprPanic "funResultTy" (pprType ty)
+funResultTy ty | Just ty' <- coreView ty = funResultTy ty'
+funResultTy (FunTy arg res) = res
+funResultTy ty = pprPanic "funResultTy" (ppr ty)
+
+funArgTy :: Type -> Type
+funArgTy ty | Just ty' <- coreView ty = funArgTy ty'
+funArgTy (FunTy arg res) = arg
+funArgTy ty = pprPanic "funArgTy" (ppr ty)
\end{code}
-
---------------------------------------------------------------------
TyConApp
~~~~~~~~
+@mkTyConApp@ is a key function, because it builds a TyConApp, FunTy or PredTy,
+as apppropriate.
\begin{code}
+mkGenTyConApp :: TyCon -> [Type] -> Type
+mkGenTyConApp tc tys
+ | isSynTyCon tc = mkSynTy tc tys
+ | otherwise = mkTyConApp tc tys
+
mkTyConApp :: TyCon -> [Type] -> Type
+-- Assumes TyCon is not a SynTyCon; use mkSynTy instead for those
mkTyConApp tycon tys
- | isFunTyCon tycon && length tys == 2
- = case tys of
- (ty1:ty2:_) -> FunTy ty1 ty2
+ | isFunTyCon tycon, [ty1,ty2] <- tys
+ = FunTy ty1 ty2
| otherwise
= ASSERT(not (isSynTyCon tycon))
TyConApp tycon tys
mkTyConTy :: TyCon -> Type
-mkTyConTy tycon = ASSERT( not (isSynTyCon tycon) )
- TyConApp tycon []
+mkTyConTy tycon = mkTyConApp tycon []
-- splitTyConApp "looks through" synonyms, because they don't
-- mean a distinct type, but all other type-constructor applications
-- including functions are returned as Just ..
+tyConAppTyCon :: Type -> TyCon
+tyConAppTyCon ty = fst (splitTyConApp ty)
+
+tyConAppArgs :: Type -> [Type]
+tyConAppArgs ty = snd (splitTyConApp ty)
+
+splitTyConApp :: Type -> (TyCon, [Type])
+splitTyConApp ty = case splitTyConApp_maybe ty of
+ Just stuff -> stuff
+ Nothing -> pprPanic "splitTyConApp" (ppr ty)
+
splitTyConApp_maybe :: Type -> Maybe (TyCon, [Type])
+splitTyConApp_maybe ty | Just ty' <- coreView ty = splitTyConApp_maybe ty'
splitTyConApp_maybe (TyConApp tc tys) = Just (tc, tys)
splitTyConApp_maybe (FunTy arg res) = Just (funTyCon, [arg,res])
-splitTyConApp_maybe (NoteTy _ ty) = splitTyConApp_maybe ty
splitTyConApp_maybe other = Nothing
-
--- splitAlgTyConApp_maybe looks for
--- *saturated* applications of *algebraic* data types
--- "Algebraic" => newtype, data type, or dictionary (not function types)
--- We return the constructors too.
-
-splitAlgTyConApp_maybe :: Type -> Maybe (TyCon, [Type], [DataCon])
-splitAlgTyConApp_maybe (TyConApp tc tys)
- | isAlgTyCon tc &&
- tyConArity tc == length tys = Just (tc, tys, tyConDataCons tc)
-splitAlgTyConApp_maybe (NoteTy _ ty) = splitAlgTyConApp_maybe ty
-splitAlgTyConApp_maybe other = Nothing
-
-splitAlgTyConApp :: Type -> (TyCon, [Type], [DataCon])
- -- Here the "algebraic" property is an *assertion*
-splitAlgTyConApp (TyConApp tc tys) = ASSERT( isAlgTyCon tc && tyConArity tc == length tys )
- (tc, tys, tyConDataCons tc)
-splitAlgTyConApp (NoteTy _ ty) = splitAlgTyConApp ty
-\end{code}
-
-"Dictionary" types are just ordinary data types, but you can
-tell from the type constructor whether it's a dictionary or not.
-
-\begin{code}
-mkDictTy :: Class -> [Type] -> Type
-mkDictTy clas tys = TyConApp (classTyCon clas) tys
-
-splitDictTy_maybe :: Type -> Maybe (Class, [Type])
-splitDictTy_maybe (TyConApp tc tys)
- | maybeToBool maybe_class
- && tyConArity tc == length tys = Just (clas, tys)
- where
- maybe_class = tyConClass_maybe tc
- Just clas = maybe_class
-
-splitDictTy_maybe (NoteTy _ ty) = splitDictTy_maybe ty
-splitDictTy_maybe other = Nothing
-
-isDictTy :: Type -> Bool
- -- This version is slightly more efficient than (maybeToBool . splitDictTy)
-isDictTy (TyConApp tc tys)
- | maybeToBool (tyConClass_maybe tc)
- && tyConArity tc == length tys
- = True
-isDictTy (NoteTy _ ty) = isDictTy ty
-isDictTy other = False
\end{code}
~~~~~
\begin{code}
-mkSynTy syn_tycon tys
- = ASSERT(isSynTyCon syn_tycon)
- NoteTy (SynNote (TyConApp syn_tycon tys))
- (substTopTy (zipVarEnv tyvars tys) body)
+mkSynTy tycon tys
+ | n_args == arity -- Exactly saturated
+ = mk_syn tys
+ | n_args > arity -- Over-saturated
+ = case splitAt arity tys of { (as,bs) -> mkAppTys (mk_syn as) bs }
+ -- Its important to use mkAppTys, rather than (foldl AppTy),
+ -- because (mk_syn as) might well return a partially-applied
+ -- type constructor; indeed, usually will!
+ | otherwise -- Un-saturated
+ = TyConApp tycon tys
+ -- For the un-saturated case we build TyConApp directly
+ -- (mkTyConApp ASSERTs that the tc isn't a SynTyCon).
+ -- Here we are relying on checkValidType to find
+ -- the error. What we can't do is use mkSynTy with
+ -- too few arg tys, because that is utterly bogus.
+
where
- (tyvars, body) = getSynTyConDefn syn_tycon
-
-isSynTy (NoteTy (SynNote _) _) = True
-isSynTy other = False
-
-deNoteType :: Type -> Type
- -- Sorry for the cute name
-deNoteType ty@(TyVarTy tyvar) = ty
-deNoteType (TyConApp tycon tys) = TyConApp tycon (map deNoteType tys)
-deNoteType (NoteTy _ ty) = deNoteType ty
-deNoteType (AppTy fun arg) = AppTy (deNoteType fun) (deNoteType arg)
-deNoteType (FunTy fun arg) = FunTy (deNoteType fun) (deNoteType arg)
-deNoteType (ForAllTy tv ty) = ForAllTy tv (deNoteType ty)
+ mk_syn tys = NoteTy (SynNote (TyConApp tycon tys))
+ (substTyWith tyvars tys body)
+
+ (tyvars, body) = ASSERT( isSynTyCon tycon ) getSynTyConDefn tycon
+ arity = tyConArity tycon
+ n_args = length tys
\end{code}
Notes on type synonyms
interfaces. Notably this plays a role in tcTySigs in TcBinds.lhs.
+ Representation types
+ ~~~~~~~~~~~~~~~~~~~~
+repType looks through
+ (a) for-alls, and
+ (b) synonyms
+ (c) predicates
+ (d) usage annotations
+ (e) all newtypes, including recursive ones
+It's useful in the back end.
+
+\begin{code}
+repType :: Type -> Type
+-- Only applied to types of kind *; hence tycons are saturated
+repType (ForAllTy _ ty) = repType ty
+repType (NoteTy _ ty) = repType ty
+repType (PredTy p) = repType (predTypeRep p)
+repType (TyConApp tc tys)
+ | isNewTyCon tc = ASSERT( tys `lengthIs` tyConArity tc )
+ repType (new_type_rep tc tys)
+repType ty = ty
+
+-- ToDo: this could be moved to the code generator, using splitTyConApp instead
+-- of inspecting the type directly.
+typePrimRep :: Type -> PrimRep
+typePrimRep ty = case repType ty of
+ TyConApp tc _ -> tyConPrimRep tc
+ FunTy _ _ -> PtrRep
+ AppTy _ _ -> PtrRep -- See note below
+ TyVarTy _ -> PtrRep
+ other -> pprPanic "typePrimRep" (ppr ty)
+ -- Types of the form 'f a' must be of kind *, not *#, so
+ -- we are guaranteed that they are represented by pointers.
+ -- The reason is that f must have kind *->*, not *->*#, because
+ -- (we claim) there is no way to constrain f's kind any other
+ -- way.
+
+-- new_type_rep doesn't ask any questions:
+-- it just expands newtype, whether recursive or not
+new_type_rep new_tycon tys = ASSERT( tys `lengthIs` tyConArity new_tycon )
+ case newTyConRep new_tycon of
+ (tvs, rep_ty) -> substTyWith tvs tys rep_ty
+\end{code}
---------------------------------------------------------------------
~~~~~~~~
\begin{code}
-mkForAllTy = ForAllTy
+mkForAllTy :: TyVar -> Type -> Type
+mkForAllTy tyvar ty
+ = mkForAllTys [tyvar] ty
mkForAllTys :: [TyVar] -> Type -> Type
mkForAllTys tyvars ty = foldr ForAllTy ty tyvars
-splitForAllTy_maybe :: Type -> Maybe (TyVar, Type)
-splitForAllTy_maybe (NoteTy _ ty) = splitForAllTy_maybe ty
-splitForAllTy_maybe (ForAllTy tyvar ty) = Just(tyvar, ty)
-splitForAllTy_maybe _ = Nothing
-
isForAllTy :: Type -> Bool
-isForAllTy (NoteTy _ ty) = isForAllTy ty
-isForAllTy (ForAllTy tyvar ty) = True
-isForAllTy _ = False
+isForAllTy (NoteTy _ ty) = isForAllTy ty
+isForAllTy (ForAllTy _ _) = True
+isForAllTy other_ty = False
+
+splitForAllTy_maybe :: Type -> Maybe (TyVar, Type)
+splitForAllTy_maybe ty = splitFAT_m ty
+ where
+ splitFAT_m ty | Just ty' <- coreView ty = splitFAT_m ty'
+ splitFAT_m (ForAllTy tyvar ty) = Just(tyvar, ty)
+ splitFAT_m _ = Nothing
splitForAllTys :: Type -> ([TyVar], Type)
splitForAllTys ty = split ty ty []
where
- split orig_ty (ForAllTy tv ty) tvs = split ty ty (tv:tvs)
- split orig_ty (NoteTy _ ty) tvs = split orig_ty ty tvs
- split orig_ty t tvs = (reverse tvs, orig_ty)
+ split orig_ty ty tvs | Just ty' <- coreView ty = split orig_ty ty' tvs
+ split orig_ty (ForAllTy tv ty) tvs = split ty ty (tv:tvs)
+ split orig_ty t tvs = (reverse tvs, orig_ty)
+
+dropForAlls :: Type -> Type
+dropForAlls ty = snd (splitForAllTys ty)
\end{code}
-@mkPiType@ makes a (->) type or a forall type, depending on whether
-it is given a type variable or a term variable.
+-- (mkPiType now in CoreUtils)
-\begin{code}
-mkPiType :: IdOrTyVar -> Type -> Type -- The more polymorphic version doesn't work...
-mkPiType v ty | isId v = mkFunTy (idType v) ty
- | otherwise = ForAllTy v ty
-\end{code}
+applyTy, applyTys
+~~~~~~~~~~~~~~~~~
+Instantiate a for-all type with one or more type arguments.
+Used when we have a polymorphic function applied to type args:
+ f t1 t2
+Then we use (applyTys type-of-f [t1,t2]) to compute the type of
+the expression.
\begin{code}
applyTy :: Type -> Type -> Type
-applyTy (NoteTy _ fun) arg = applyTy fun arg
-applyTy (ForAllTy tv ty) arg = substTy (mkVarEnv [(tv,arg)]) ty
+applyTy ty arg | Just ty' <- coreView ty = applyTy ty' arg
+applyTy (ForAllTy tv ty) arg = substTyWith [tv] [arg] ty
applyTy other arg = panic "applyTy"
applyTys :: Type -> [Type] -> Type
-applyTys fun_ty arg_tys
- = go [] fun_ty arg_tys
- where
- go env ty [] = substTy (mkVarEnv env) ty
- go env (NoteTy _ fun) args = go env fun args
- go env (ForAllTy tv ty) (arg:args) = go ((tv,arg):env) ty args
- go env other args = panic "applyTys"
+-- This function is interesting because
+-- a) the function may have more for-alls than there are args
+-- b) less obviously, it may have fewer for-alls
+-- For case (b) think of
+-- applyTys (forall a.a) [forall b.b, Int]
+-- This really can happen, via dressing up polymorphic types with newtype
+-- clothing. Here's an example:
+-- newtype R = R (forall a. a->a)
+-- foo = case undefined :: R of
+-- R f -> f ()
+
+applyTys orig_fun_ty [] = orig_fun_ty
+applyTys orig_fun_ty arg_tys
+ | n_tvs == n_args -- The vastly common case
+ = substTyWith tvs arg_tys rho_ty
+ | n_tvs > n_args -- Too many for-alls
+ = substTyWith (take n_args tvs) arg_tys
+ (mkForAllTys (drop n_args tvs) rho_ty)
+ | otherwise -- Too many type args
+ = ASSERT2( n_tvs > 0, ppr orig_fun_ty ) -- Zero case gives infnite loop!
+ applyTys (substTyWith tvs (take n_tvs arg_tys) rho_ty)
+ (drop n_tvs arg_tys)
+ where
+ (tvs, rho_ty) = splitForAllTys orig_fun_ty
+ n_tvs = length tvs
+ n_args = length arg_tys
\end{code}
%************************************************************************
%* *
-\subsection{Stuff to do with the source-language types}
+\subsection{Source types}
%* *
%************************************************************************
-\begin{code}
-type RhoType = Type
-type TauType = Type
-type ThetaType = [(Class, [Type])]
-type SigmaType = Type
-\end{code}
+A "source type" is a type that is a separate type as far as the type checker is
+concerned, but which has low-level representation as far as the back end is concerned.
-@isTauTy@ tests for nested for-alls.
+Source types are always lifted.
-\begin{code}
-isTauTy :: Type -> Bool
-isTauTy (TyVarTy v) = True
-isTauTy (TyConApp _ tys) = all isTauTy tys
-isTauTy (AppTy a b) = isTauTy a && isTauTy b
-isTauTy (FunTy a b) = isTauTy a && isTauTy b
-isTauTy (NoteTy _ ty) = isTauTy ty
-isTauTy other = False
-\end{code}
+The key function is predTypeRep which gives the representation of a source type:
\begin{code}
-mkRhoTy :: [(Class, [Type])] -> Type -> Type
-mkRhoTy theta ty = foldr (\(c,t) r -> FunTy (mkDictTy c t) r) ty theta
-
-splitRhoTy :: Type -> ([(Class, [Type])], Type)
-splitRhoTy ty = split ty ty []
- where
- split orig_ty (FunTy arg res) ts = case splitDictTy_maybe arg of
- Just pair -> split res res (pair:ts)
- Nothing -> (reverse ts, orig_ty)
- split orig_ty (NoteTy _ ty) ts = split orig_ty ty ts
- split orig_ty ty ts = (reverse ts, orig_ty)
+mkPredTy :: PredType -> Type
+mkPredTy pred = PredTy pred
+
+mkPredTys :: ThetaType -> [Type]
+mkPredTys preds = map PredTy preds
+
+predTypeRep :: PredType -> Type
+-- Convert a PredType to its "representation type";
+-- the post-type-checking type used by all the Core passes of GHC.
+-- Unwraps only the outermost level; for example, the result might
+-- be a newtype application
+predTypeRep (IParam _ ty) = ty
+predTypeRep (ClassP clas tys) = mkTyConApp (classTyCon clas) tys
+ -- Result might be a newtype application, but the consumer will
+ -- look through that too if necessary
\end{code}
+%************************************************************************
+%* *
+ NewTypes
+%* *
+%************************************************************************
\begin{code}
-mkSigmaTy tyvars theta tau = mkForAllTys tyvars (mkRhoTy theta tau)
-
-splitSigmaTy :: Type -> ([TyVar], [(Class, [Type])], Type)
-splitSigmaTy ty =
- (tyvars, theta, tau)
- where
- (tyvars,rho) = splitForAllTys ty
- (theta,tau) = splitRhoTy rho
+splitRecNewType_maybe :: Type -> Maybe Type
+-- Sometimes we want to look through a recursive newtype, and that's what happens here
+-- It only strips *one layer* off, so the caller will usually call itself recursively
+-- Only applied to types of kind *, hence the newtype is always saturated
+splitRecNewType_maybe ty | Just ty' <- coreView ty = splitRecNewType_maybe ty'
+splitRecNewType_maybe (TyConApp tc tys)
+ | isNewTyCon tc
+ = ASSERT( tys `lengthIs` tyConArity tc ) -- splitRecNewType_maybe only be applied
+ -- to *types* (of kind *)
+ ASSERT( isRecursiveTyCon tc ) -- Guaranteed by coreView
+ case newTyConRhs tc of
+ (tvs, rep_ty) -> Just (substTyWith tvs tys rep_ty)
+
+splitRecNewType_maybe other = Nothing
\end{code}
typeKind :: Type -> Kind
typeKind (TyVarTy tyvar) = tyVarKind tyvar
-typeKind (TyConApp tycon tys) = foldr (\_ k -> funResultTy k) (tyConKind tycon) tys
+typeKind (TyConApp tycon tys) = foldr (\_ k -> kindFunResult k) (tyConKind tycon) tys
typeKind (NoteTy _ ty) = typeKind ty
-typeKind (AppTy fun arg) = funResultTy (typeKind fun)
-typeKind (FunTy fun arg) = typeKindF arg
-typeKind (ForAllTy _ ty) = typeKindF ty -- We could make this a new kind polyTypeKind
- -- to prevent a forall type unifying with a
- -- boxed type variable, but I didn't think it
- -- was worth it yet.
-
--- The complication is that a *function* is boxed even if
--- its *result* type is unboxed. Seems wierd.
-
-typeKindF :: Type -> Kind
-typeKindF (NoteTy _ ty) = typeKindF ty
-typeKindF (FunTy _ ty) = typeKindF ty
-typeKindF (ForAllTy _ ty) = typeKindF ty
-typeKindF other = fix_up (typeKind other)
- where
- fix_up (TyConApp kc _) | kc == typeCon = boxedTypeKind
- -- Functions at the type level are always boxed
- fix_up (NoteTy _ kind) = fix_up kind
- fix_up kind = kind
+typeKind (PredTy _) = liftedTypeKind -- Predicates are always
+ -- represented by lifted types
+typeKind (AppTy fun arg) = kindFunResult (typeKind fun)
+typeKind (FunTy arg res) = liftedTypeKind
+typeKind (ForAllTy tv ty) = typeKind ty
\end{code}
~~~~~~~~~~~~~~~~~~~~~~~~
\begin{code}
tyVarsOfType :: Type -> TyVarSet
-
tyVarsOfType (TyVarTy tv) = unitVarSet tv
tyVarsOfType (TyConApp tycon tys) = tyVarsOfTypes tys
tyVarsOfType (NoteTy (FTVNote tvs) ty2) = tvs
-tyVarsOfType (NoteTy (SynNote ty1) ty2) = tyVarsOfType ty1
+tyVarsOfType (NoteTy (SynNote ty1) ty2) = tyVarsOfType ty2 -- See note [Syn] below
+tyVarsOfType (PredTy sty) = tyVarsOfPred sty
tyVarsOfType (FunTy arg res) = tyVarsOfType arg `unionVarSet` tyVarsOfType res
tyVarsOfType (AppTy fun arg) = tyVarsOfType fun `unionVarSet` tyVarsOfType arg
tyVarsOfType (ForAllTy tyvar ty) = tyVarsOfType ty `minusVarSet` unitVarSet tyvar
-tyVarsOfTypes :: [Type] -> TyVarSet
-tyVarsOfTypes tys = foldr (unionVarSet.tyVarsOfType) emptyVarSet tys
+-- Note [Syn]
+-- Consider
+-- type T a = Int
+-- What are the free tyvars of (T x)? Empty, of course!
+-- Here's the example that Ralf Laemmel showed me:
+-- foo :: (forall a. C u a -> C u a) -> u
+-- mappend :: Monoid u => u -> u -> u
+--
+-- bar :: Monoid u => u
+-- bar = foo (\t -> t `mappend` t)
+-- We have to generalise at the arg to f, and we don't
+-- want to capture the constraint (Monad (C u a)) because
+-- it appears to mention a. Pretty silly, but it was useful to him.
--- Add a Note with the free tyvars to the top of the type
-addFreeTyVars :: Type -> Type
-addFreeTyVars ty@(NoteTy (FTVNote _) _) = ty
-addFreeTyVars ty = NoteTy (FTVNote (tyVarsOfType ty)) ty
-
--- Find the free names of a type, including the type constructors and classes it mentions
-namesOfType :: Type -> NameSet
-namesOfType (TyVarTy tv) = unitNameSet (getName tv)
-namesOfType (TyConApp tycon tys) = unitNameSet (getName tycon) `unionNameSets`
- namesOfTypes tys
-namesOfType (NoteTy (SynNote ty1) ty2) = namesOfType ty1
-namesOfType (NoteTy other_note ty2) = namesOfType ty2
-namesOfType (FunTy arg res) = namesOfType arg `unionNameSets` namesOfType res
-namesOfType (AppTy fun arg) = namesOfType fun `unionNameSets` namesOfType arg
-namesOfType (ForAllTy tyvar ty) = namesOfType ty `minusNameSet` unitNameSet (getName tyvar)
-
-namesOfTypes tys = foldr (unionNameSets . namesOfType) emptyNameSet tys
-\end{code}
+tyVarsOfTypes :: [Type] -> TyVarSet
+tyVarsOfTypes tys = foldr (unionVarSet.tyVarsOfType) emptyVarSet tys
-%************************************************************************
-%* *
-\subsection{Instantiating a type}
-%* *
-%************************************************************************
-
-@substTy@ applies a substitution to a type. It deals correctly with name capture.
-
-\begin{code}
-substTy :: TyVarSubst -> Type -> Type
-substTy tenv ty
- | isEmptyVarEnv tenv = ty
- | otherwise = subst_ty tenv tset ty
- where
- tset = foldVarEnv (unionVarSet . tyVarsOfType) emptyVarSet tenv
- -- If ty doesn't have any for-alls, then this thunk
- -- will never be evaluated
-
-substTheta :: TyVarSubst -> ThetaType -> ThetaType
-substTheta tenv theta
- | isEmptyVarEnv tenv = theta
- | otherwise = [(clas, map (subst_ty tenv tset) tys) | (clas, tys) <- theta]
- where
- tset = foldVarEnv (unionVarSet . tyVarsOfType) emptyVarSet tenv
- -- If ty doesn't have any for-alls, then this thunk
- -- will never be evaluated
-
-substTopTy :: TyVarSubst -> Type -> Type
-substTopTy = substTy -- Called when doing top-level substitutions.
- -- Here we expect that the free vars of the range of the
- -- substitution will be empty; but during typechecking I'm
- -- a bit dubious about that (mutable tyvars bouund to Int, say)
- -- So I've left it as substTy for the moment. SLPJ Nov 98
-substTopTheta = substTheta
-\end{code}
-
-@fullSubstTy@ is like @substTy@ except that it needs to be given a set
-of in-scope type variables. In exchange it's a bit more efficient, at least
-if you happen to have that set lying around.
-
-\begin{code}
-fullSubstTy :: TyVarSubst -- Substitution to apply
- -> TyVarSet -- Superset of the free tyvars of
- -- the range of the tyvar env
- -> Type -> Type
--- ASSUMPTION: The substitution is idempotent.
--- Equivalently: No tyvar is both in scope, and in the domain of the substitution.
-fullSubstTy tenv tset ty | isEmptyVarEnv tenv = ty
- | otherwise = subst_ty tenv tset ty
-
--- subst_ty does the business
-subst_ty tenv tset ty
- = go ty
- where
- go (TyConApp tc tys) = let args = map go tys
- in args `seqList` TyConApp tc args
- go (NoteTy (SynNote ty1) ty2) = NoteTy (SynNote $! (go ty1)) $! (go ty2)
- go (NoteTy (FTVNote _) ty2) = go ty2 -- Discard the free tyvar note
- go (FunTy arg res) = (FunTy $! (go arg)) $! (go res)
- go (AppTy fun arg) = mkAppTy (go fun) $! (go arg)
- go ty@(TyVarTy tv) = case (lookupVarEnv tenv tv) of
- Nothing -> ty
- Just ty' -> ty'
- go (ForAllTy tv ty) = case substTyVar tenv tset tv of
- (tenv', tset', tv') -> ForAllTy tv' $! (subst_ty tenv' tset' ty)
-
-substTyVar :: TyVarSubst -> TyVarSet -> TyVar
- -> (TyVarSubst, TyVarSet, TyVar)
+tyVarsOfPred :: PredType -> TyVarSet
+tyVarsOfPred (IParam _ ty) = tyVarsOfType ty
+tyVarsOfPred (ClassP _ tys) = tyVarsOfTypes tys
-substTyVar tenv tset tv
- | not (tv `elemVarSet` tset) -- No need to clone
- -- But must delete from substitution
- = (tenv `delVarEnv` tv, tset `extendVarSet` tv, tv)
+tyVarsOfTheta :: ThetaType -> TyVarSet
+tyVarsOfTheta = foldr (unionVarSet . tyVarsOfPred) emptyVarSet
- | otherwise -- The forall's variable is in scope so
- -- we'd better rename it away from the in-scope variables
- -- Extending the substitution to do this renaming also
- -- has the (correct) effect of discarding any existing
- -- substitution for that variable
- = (extendVarEnv tenv tv (TyVarTy tv'), tset `extendVarSet` tv', tv')
- where
- tv' = uniqAway tset tv
+-- Add a Note with the free tyvars to the top of the type
+addFreeTyVars :: Type -> Type
+addFreeTyVars ty@(NoteTy (FTVNote _) _) = ty
+addFreeTyVars ty = NoteTy (FTVNote (tyVarsOfType ty)) ty
\end{code}
-
%************************************************************************
%* *
\subsection{TidyType}
It doesn't change the uniques at all, just the print names.
\begin{code}
-tidyTyVar :: TidyEnv -> TyVar -> (TidyEnv, TyVar)
-tidyTyVar env@(tidy_env, subst) tyvar
- = case lookupVarEnv subst tyvar of
-
- Just tyvar' -> -- Already substituted
- (env, tyvar')
-
- Nothing -> -- Make a new nice name for it
-
- case tidyOccName tidy_env (getOccName name) of
- (tidy', occ') -> -- New occname reqd
- ((tidy', subst'), tyvar')
- where
- subst' = extendVarEnv subst tyvar tyvar'
- tyvar' = setTyVarName tyvar name'
- name' = mkLocalName (getUnique name) occ' noSrcLoc
- -- Note: make a *user* tyvar, so it printes nicely
- -- Could extract src loc, but no need.
+tidyTyVarBndr :: TidyEnv -> TyVar -> (TidyEnv, TyVar)
+tidyTyVarBndr (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' = mkInternalName (getUnique name) occ' noSrcLoc
+ -- Note: make a *user* tyvar, so it printes nicely
+ -- Could extract src loc, but no need.
where
name = tyVarName tyvar
-tidyTyVars env tyvars = mapAccumL tidyTyVar env tyvars
+tidyFreeTyVars :: TidyEnv -> TyVarSet -> TidyEnv
+-- Add the free tyvars 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
+tidyOpenTyVar env@(tidy_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@(tidy_env, subst) ty
go (TyConApp tycon tys) = let args = map go tys
in args `seqList` TyConApp tycon args
go (NoteTy note ty) = (NoteTy $! (go_note note)) $! (go ty)
+ 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 tv' $! (tidyType env' ty)
- where
- (env', tv') = tidyTyVar env tv
+ go (ForAllTy tv ty) = ForAllTy tvp $! (tidyType envp ty)
+ where
+ (envp, tvp) = tidyTyVarBndr env tv
go_note (SynNote ty) = SynNote $! (go ty)
go_note note@(FTVNote ftvs) = note -- No need to tidy the free tyvars
-tidyTypes env tys = map (tidyType env) tys
+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)
\end{code}
-@tidyOpenType@ grabs the free type varibles, tidies them
+@tidyOpenType@ grabs the free type variables, tidies them
and then uses @tidyType@ to work over the type itself
\begin{code}
tidyOpenType env ty
= (env', tidyType env' ty)
where
- env' = foldl go env (varSetElems (tyVarsOfType ty))
- go env tyvar = fst (tidyTyVar env tyvar)
+ env' = tidyFreeTyVars env (tyVarsOfType ty)
tidyOpenTypes :: TidyEnv -> [Type] -> (TidyEnv, [Type])
tidyOpenTypes env tys = mapAccumL tidyOpenType env tys
\end{code}
+
%************************************************************************
%* *
-\subsection{Boxedness and liftedness}
+\subsection{Liftedness}
%* *
%************************************************************************
\begin{code}
-isUnboxedType :: Type -> Bool
-isUnboxedType ty = not (isFollowableRep (typePrimRep ty))
-
isUnLiftedType :: Type -> Bool
-isUnLiftedType ty = case splitTyConApp_maybe ty of
- Just (tc, ty_args) -> isUnLiftedTyCon tc
- other -> False
+ -- isUnLiftedType returns True for forall'd unlifted types:
+ -- x :: forall a. Int#
+ -- I found bindings like these were getting floated to the top level.
+ -- They are pretty bogus types, mind you. It would be better never to
+ -- construct them
+
+isUnLiftedType ty | Just ty' <- coreView ty = isUnLiftedType ty'
+isUnLiftedType (ForAllTy tv ty) = isUnLiftedType ty
+isUnLiftedType (TyConApp tc _) = isUnLiftedTyCon tc
+isUnLiftedType other = False
isUnboxedTupleType :: Type -> Bool
isUnboxedTupleType ty = case splitTyConApp_maybe ty of
-- Should only be applied to *types*; hence the assert
isAlgType :: Type -> Bool
isAlgType ty = case splitTyConApp_maybe ty of
- Just (tc, ty_args) -> ASSERT( length ty_args == tyConArity tc )
+ Just (tc, ty_args) -> ASSERT( ty_args `lengthIs` tyConArity tc )
isAlgTyCon tc
other -> False
+\end{code}
--- Should only be applied to *types*; hence the assert
-isDataType :: Type -> Bool
-isDataType ty = case splitTyConApp_maybe ty of
- Just (tc, ty_args) -> ASSERT( length ty_args == tyConArity tc )
- isDataTyCon tc
+@isStrictType@ computes whether an argument (or let RHS) should
+be computed strictly or lazily, based only on its type.
+Works just like isUnLiftedType, except that it has a special case
+for dictionaries. Since it takes account of ClassP, you might think
+this function should be in TcType, but isStrictType is used by DataCon,
+which is below TcType in the hierarchy, so it's convenient to put it here.
+
+\begin{code}
+isStrictType (PredTy pred) = isStrictPred pred
+isStrictType ty | Just ty' <- coreView ty = isStrictType ty'
+isStrictType (ForAllTy tv ty) = isStrictType ty
+isStrictType (TyConApp tc _) = isUnLiftedTyCon tc
+isStrictType other = False
+
+isStrictPred (ClassP clas _) = opt_DictsStrict && not (isNewTyCon (classTyCon clas))
+isStrictPred other = False
+ -- We may be strict in dictionary types, but only if it
+ -- has more than one component.
+ -- [Being strict in a single-component dictionary risks
+ -- poking the dictionary component, which is wrong.]
+\end{code}
+
+\begin{code}
+isPrimitiveType :: Type -> Bool
+-- Returns types that are opaque to Haskell.
+-- Most of these are unlifted, but now that we interact with .NET, we
+-- may have primtive (foreign-imported) types that are lifted
+isPrimitiveType ty = case splitTyConApp_maybe ty of
+ Just (tc, ty_args) -> ASSERT( ty_args `lengthIs` tyConArity tc )
+ isPrimTyCon tc
other -> False
+\end{code}
-typePrimRep :: Type -> PrimRep
-typePrimRep ty = case splitTyConApp_maybe ty of
- Just (tc, ty_args) -> tyConPrimRep tc
- other -> PtrRep
+
+%************************************************************************
+%* *
+\subsection{Sequencing on types
+%* *
+%************************************************************************
+
+\begin{code}
+seqType :: Type -> ()
+seqType (TyVarTy tv) = tv `seq` ()
+seqType (AppTy t1 t2) = seqType t1 `seq` seqType t2
+seqType (FunTy t1 t2) = seqType t1 `seq` seqType t2
+seqType (NoteTy note t2) = seqNote note `seq` seqType t2
+seqType (PredTy p) = seqPred p
+seqType (TyConApp tc tys) = tc `seq` seqTypes tys
+seqType (ForAllTy tv ty) = tv `seq` seqType ty
+
+seqTypes :: [Type] -> ()
+seqTypes [] = ()
+seqTypes (ty:tys) = seqType ty `seq` seqTypes tys
+
+seqNote :: TyNote -> ()
+seqNote (SynNote ty) = seqType ty
+seqNote (FTVNote set) = sizeUniqSet set `seq` ()
+
+seqPred :: PredType -> ()
+seqPred (ClassP c tys) = c `seq` seqTypes tys
+seqPred (IParam n ty) = n `seq` seqType ty
\end{code}
+
%************************************************************************
%* *
-\subsection{Equality on types}
+ Comparison of types
+ (We don't use instances so that we know where it happens)
%* *
%************************************************************************
-For the moment at least, type comparisons don't work if
-there are embedded for-alls.
+Two flavours:
+
+* tcEqType, tcCmpType do *not* look through newtypes, PredTypes
+* coreEqType *does* look through them
+
+Note that eqType can respond 'False' for partial applications of newtypes.
+Consider
+ newtype Parser m a = MkParser (Foogle m a)
+Does
+ Monad (Parser m) `eqType` Monad (Foogle m)
+Well, yes, but eqType won't see that they are the same.
+I don't think this is harmful, but it's soemthing to watch out for.
+
+First, the external interface
+
+\begin{code}
+coreEqType :: Type -> Type -> Bool
+coreEqType t1 t2 = isEqual $ cmpType (deepCoreView t1) (deepCoreView t2)
+
+tcEqType :: Type -> Type -> Bool
+tcEqType t1 t2 = isEqual $ cmpType t1 t2
+
+tcEqTypes :: [Type] -> [Type] -> Bool
+tcEqTypes tys1 tys2 = isEqual $ cmpTypes tys1 tys2
+
+tcCmpType :: Type -> Type -> Ordering
+tcCmpType t1 t2 = cmpType t1 t2
+
+tcCmpTypes :: [Type] -> [Type] -> Ordering
+tcCmpTypes tys1 tys2 = cmpTypes tys1 tys2
+
+tcEqPred :: PredType -> PredType -> Bool
+tcEqPred p1 p2 = isEqual $ cmpPred p1 p2
+
+tcCmpPred :: PredType -> PredType -> Ordering
+tcCmpPred p1 p2 = cmpPred p1 p2
+
+tcEqTypeX :: RnEnv2 -> Type -> Type -> Bool
+tcEqTypeX env t1 t2 = isEqual $ cmpTypeX env t1 t2
+\end{code}
+
+Now here comes the real worker
\begin{code}
-instance Eq Type where
- ty1 == ty2 = case ty1 `cmpTy` ty2 of { EQ -> True; other -> False }
+cmpType :: Type -> Type -> Ordering
+cmpType t1 t2 = cmpTypeX rn_env t1 t2
+ where
+ rn_env = mkRnEnv2 (mkInScopeSet (tyVarsOfType t1 `unionVarSet` tyVarsOfType t2))
-instance Ord Type where
- compare ty1 ty2 = cmpTy ty1 ty2
+cmpTypes :: [Type] -> [Type] -> Ordering
+cmpTypes ts1 ts2 = cmpTypesX rn_env ts1 ts2
+ where
+ rn_env = mkRnEnv2 (mkInScopeSet (tyVarsOfTypes ts1 `unionVarSet` tyVarsOfTypes ts2))
-cmpTy :: Type -> Type -> Ordering
-cmpTy ty1 ty2
- = cmp emptyVarEnv ty1 ty2
+cmpPred :: PredType -> PredType -> Ordering
+cmpPred p1 p2 = cmpPredX rn_env p1 p2
where
- -- The "env" maps type variables in ty1 to type variables in ty2
- -- So when comparing for-alls.. (forall tv1 . t1) (forall tv2 . t2)
- -- we in effect substitute tv2 for tv1 in t1 before continuing
- lookup env tv1 = case lookupVarEnv env tv1 of
- Just tv2 -> tv2
- Nothing -> tv1
-
- -- Get rid of NoteTy
- cmp env (NoteTy _ ty1) ty2 = cmp env ty1 ty2
- cmp env ty1 (NoteTy _ ty2) = cmp env ty1 ty2
+ rn_env = mkRnEnv2 (mkInScopeSet (tyVarsOfPred p1 `unionVarSet` tyVarsOfPred p2))
+
+cmpTypeX :: RnEnv2 -> Type -> Type -> Ordering -- Main workhorse
+
+-- NB: we *cannot* short-cut the newtype comparison thus:
+-- eqTypeX env (NewTcApp tc1 tys1) (NewTcApp tc2 tys2)
+-- | (tc1 == tc2) = (eqTypeXs env tys1 tys2)
+--
+-- Consider:
+-- newtype T a = MkT [a]
+-- newtype Foo m = MkFoo (forall a. m a -> Int)
+-- w1 :: Foo []
+-- w1 = ...
+--
+-- w2 :: Foo T
+-- w2 = MkFoo (\(MkT x) -> case w1 of MkFoo f -> f x)
+--
+-- We end up with w2 = w1; so we need that Foo T = Foo []
+-- but we can only expand saturated newtypes, so just comparing
+-- T with [] won't do.
+
+cmpTypeX env (TyVarTy tv1) (TyVarTy tv2) = rnOccL env tv1 `compare` rnOccR env tv2
+cmpTypeX env (ForAllTy tv1 t1) (ForAllTy tv2 t2) = cmpTypeX (rnBndr2 env tv1 tv2) t1 t2
+cmpTypeX env (AppTy s1 t1) (AppTy s2 t2) = cmpTypeX env s1 s2 `thenCmp` cmpTypeX env t1 t2
+cmpTypeX env (FunTy s1 t1) (FunTy s2 t2) = cmpTypeX env s1 s2 `thenCmp` cmpTypeX env t1 t2
+cmpTypeX env (PredTy p1) (PredTy p2) = cmpPredX env p1 p2
+cmpTypeX env (TyConApp tc1 tys1) (TyConApp tc2 tys2) = (tc1 `compare` tc2) `thenCmp` cmpTypesX env tys1 tys2
+cmpTypeX env (NoteTy _ t1) t2 = cmpTypeX env t1 t2
+cmpTypeX env t1 (NoteTy _ t2) = cmpTypeX env t1 t2
+
+ -- Deal with the rest: TyVarTy < AppTy < FunTy < TyConApp < ForAllTy < PredTy
+cmpTypeX env (AppTy _ _) (TyVarTy _) = GT
- -- Deal with equal constructors
- cmp env (TyVarTy tv1) (TyVarTy tv2) = lookup env tv1 `compare` tv2
- cmp env (AppTy f1 a1) (AppTy f2 a2) = cmp env f1 f2 `thenCmp` cmp env a1 a2
- cmp env (FunTy f1 a1) (FunTy f2 a2) = cmp env f1 f2 `thenCmp` cmp env a1 a2
- cmp env (TyConApp tc1 tys1) (TyConApp tc2 tys2) = (tc1 `compare` tc2) `thenCmp` (cmps env tys1 tys2)
- cmp env (ForAllTy tv1 t1) (ForAllTy tv2 t2) = cmp (extendVarEnv env tv1 tv2) t1 t2
+cmpTypeX env (FunTy _ _) (TyVarTy _) = GT
+cmpTypeX env (FunTy _ _) (AppTy _ _) = GT
- -- Deal with the rest: TyVarTy < AppTy < FunTy < TyConApp < ForAllTy
- cmp env (AppTy _ _) (TyVarTy _) = GT
+cmpTypeX env (TyConApp _ _) (TyVarTy _) = GT
+cmpTypeX env (TyConApp _ _) (AppTy _ _) = GT
+cmpTypeX env (TyConApp _ _) (FunTy _ _) = GT
- cmp env (FunTy _ _) (TyVarTy _) = GT
- cmp env (FunTy _ _) (AppTy _ _) = GT
-
- cmp env (TyConApp _ _) (TyVarTy _) = GT
- cmp env (TyConApp _ _) (AppTy _ _) = GT
- cmp env (TyConApp _ _) (FunTy _ _) = GT
-
- cmp env (ForAllTy _ _) other = GT
-
- cmp env _ _ = LT
+cmpTypeX env (ForAllTy _ _) (TyVarTy _) = GT
+cmpTypeX env (ForAllTy _ _) (AppTy _ _) = GT
+cmpTypeX env (ForAllTy _ _) (FunTy _ _) = GT
+cmpTypeX env (ForAllTy _ _) (TyConApp _ _) = GT
+
+cmpTypeX env (PredTy _) t2 = GT
+
+cmpTypeX env _ _ = LT
+
+-------------
+cmpTypesX :: RnEnv2 -> [Type] -> [Type] -> Ordering
+cmpTypesX env [] [] = EQ
+cmpTypesX env (t1:tys1) (t2:tys2) = cmpTypeX env t1 t2 `thenCmp` cmpTypesX env tys1 tys2
+cmpTypesX env [] tys = LT
+cmpTypesX env ty [] = GT
+
+-------------
+cmpPredX :: RnEnv2 -> PredType -> PredType -> Ordering
+cmpPredX env (IParam n1 ty1) (IParam n2 ty2) = (n1 `compare` n2) `thenCmp` cmpTypeX env ty1 ty2
+ -- Compare types as well as names for implicit parameters
+ -- This comparison is used exclusively (I think) for the
+ -- finite map built in TcSimplify
+cmpPredX env (ClassP c1 tys1) (ClassP c2 tys2) = (c1 `compare` c2) `thenCmp` cmpTypesX env tys1 tys2
+cmpPredX env (IParam _ _) (ClassP _ _) = LT
+cmpPredX env (ClassP _ _) (IParam _ _) = GT
+\end{code}
+
+PredTypes are used as a FM key in TcSimplify,
+so we take the easy path and make them an instance of Ord
+
+\begin{code}
+instance Eq PredType where { (==) = tcEqPred }
+instance Ord PredType where { compare = tcCmpPred }
+\end{code}
+
+
+%************************************************************************
+%* *
+ Type substitutions
+%* *
+%************************************************************************
+
+\begin{code}
+data TvSubst
+ = TvSubst InScopeSet -- The in-scope type variables
+ TvSubstEnv -- The substitution itself
+ -- See Note [Apply Once]
+
+{- ----------------------------------------------------------
+ Note [Apply Once]
+
+We use TvSubsts to instantiate things, and we might instantiate
+ forall a b. ty
+\with the types
+ [a, b], or [b, a].
+So the substition might go [a->b, b->a]. A similar situation arises in Core
+when we find a beta redex like
+ (/\ a /\ b -> e) b a
+Then we also end up with a substition that permutes type variables. Other
+variations happen to; for example [a -> (a, b)].
+
+ ***************************************************
+ *** So a TvSubst must be applied precisely once ***
+ ***************************************************
+
+A TvSubst is not idempotent, but, unlike the non-idempotent substitution
+we use during unifications, it must not be repeatedly applied.
+-------------------------------------------------------------- -}
+
+
+type TvSubstEnv = TyVarEnv Type
+ -- A TvSubstEnv is used both inside a TvSubst (with the apply-once
+ -- invariant discussed in Note [Apply Once]), and also independently
+ -- in the middle of matching, and unification (see Types.Unify)
+ -- So you have to look at the context to know if it's idempotent or
+ -- apply-once or whatever
+
+composeTvSubst :: InScopeSet -> TvSubstEnv -> TvSubstEnv -> TvSubstEnv
+-- (compose env1 env2)(x) is env1(env2(x)); i.e. apply env2 then env1
+-- It assumes that both are idempotent
+composeTvSubst in_scope env1 env2
+ = env1 `plusVarEnv` mapVarEnv (substTy subst1) env2
+ -- First apply env1 to the range of env2
+ -- Then combine the two, making sure that env1 loses if
+ -- both bind the same variable; that's why env1 is the
+ -- *left* argument to plusVarEnv, becuause the right arg wins
+ where
+ subst1 = TvSubst in_scope env1
+
+emptyTvSubst = TvSubst emptyInScopeSet emptyVarEnv
+isEmptyTvSubst :: TvSubst -> Bool
+isEmptyTvSubst (TvSubst _ env) = isEmptyVarEnv env
+
+getTvSubstEnv :: TvSubst -> TvSubstEnv
+getTvSubstEnv (TvSubst _ env) = env
+
+getTvInScope :: TvSubst -> InScopeSet
+getTvInScope (TvSubst in_scope _) = in_scope
+
+isInScope :: Var -> TvSubst -> Bool
+isInScope v (TvSubst in_scope _) = v `elemInScopeSet` in_scope
+
+setTvSubstEnv :: TvSubst -> TvSubstEnv -> TvSubst
+setTvSubstEnv (TvSubst in_scope _) env = TvSubst in_scope env
+
+extendTvInScope :: TvSubst -> [Var] -> TvSubst
+extendTvInScope (TvSubst in_scope env) vars = TvSubst (extendInScopeSetList in_scope vars) env
+
+extendTvSubst :: TvSubst -> TyVar -> Type -> TvSubst
+extendTvSubst (TvSubst in_scope env) tv ty = TvSubst in_scope (extendVarEnv env tv ty)
+
+extendTvSubstList :: TvSubst -> [TyVar] -> [Type] -> TvSubst
+extendTvSubstList (TvSubst in_scope env) tvs tys
+ = TvSubst in_scope (extendVarEnvList env (tvs `zip` tys))
+
+-- mkTvSubst and zipTvSubst generate the in-scope set from
+-- the types given; but it's just a thunk so with a bit of luck
+-- it'll never be evaluated
- cmps env [] [] = EQ
- cmps env (t:ts) [] = GT
- cmps env [] (t:ts) = LT
- cmps env (t1:t1s) (t2:t2s) = cmp env t1 t2 `thenCmp` cmps env t1s t2s
+mkTvSubst :: TvSubstEnv -> TvSubst
+mkTvSubst env
+ = TvSubst (mkInScopeSet (tyVarsOfTypes (varEnvElts env))) env
+
+zipTvSubst :: [TyVar] -> [Type] -> TvSubst
+zipTvSubst tyvars tys
+ = TvSubst (mkInScopeSet (tyVarsOfTypes tys)) (zipTyEnv tyvars tys)
+
+-- mkTopTvSubst is called when doing top-level substitutions.
+-- Here we expect that the free vars of the range of the
+-- substitution will be empty.
+mkTopTvSubst :: [(TyVar, Type)] -> TvSubst
+mkTopTvSubst prs = TvSubst emptyInScopeSet (mkVarEnv prs)
+
+zipTopTvSubst :: [TyVar] -> [Type] -> TvSubst
+zipTopTvSubst tyvars tys = TvSubst emptyInScopeSet (zipTyEnv tyvars tys)
+
+zipTyEnv :: [TyVar] -> [Type] -> TvSubstEnv
+zipTyEnv tyvars tys
+#ifdef DEBUG
+ | length tyvars /= length tys
+ = pprTrace "mkTopTvSubst" (ppr tyvars $$ ppr tys) emptyVarEnv
+ | otherwise
+#endif
+ = zip_ty_env tyvars tys emptyVarEnv
+
+-- Later substitutions in the list over-ride earlier ones,
+-- but there should be no loops
+zip_ty_env [] [] env = env
+zip_ty_env (tv:tvs) (ty:tys) env = zip_ty_env tvs tys (extendVarEnv env tv ty)
+ -- There used to be a special case for when
+ -- ty == TyVarTy tv
+ -- (a not-uncommon case) in which case the substitution was dropped.
+ -- But the type-tidier changes the print-name of a type variable without
+ -- changing the unique, and that led to a bug. Why? Pre-tidying, we had
+ -- a type {Foo t}, where Foo is a one-method class. So Foo is really a newtype.
+ -- And it happened that t was the type variable of the class. Post-tiding,
+ -- it got turned into {Foo t2}. The ext-core printer expanded this using
+ -- sourceTypeRep, but that said "Oh, t == t2" because they have the same unique,
+ -- and so generated a rep type mentioning t not t2.
+ --
+ -- Simplest fix is to nuke the "optimisation"
+
+instance Outputable TvSubst where
+ ppr (TvSubst ins env)
+ = sep[ ptext SLIT("<TvSubst"),
+ nest 2 (ptext SLIT("In scope:") <+> ppr ins),
+ nest 2 (ptext SLIT("Env:") <+> ppr env) ]
+\end{code}
+
+%************************************************************************
+%* *
+ Performing type substitutions
+%* *
+%************************************************************************
+
+\begin{code}
+substTyWith :: [TyVar] -> [Type] -> Type -> Type
+substTyWith tvs tys = substTy (zipTvSubst tvs tys)
+
+substTy :: TvSubst -> Type -> Type
+substTy subst ty | isEmptyTvSubst subst = ty
+ | otherwise = subst_ty subst ty
+
+substTys :: TvSubst -> [Type] -> [Type]
+substTys subst tys | isEmptyTvSubst subst = tys
+ | otherwise = map (subst_ty subst) tys
+
+deShadowTy :: Type -> Type -- Remove any shadowing from the type
+deShadowTy ty = subst_ty emptyTvSubst ty
+
+substTheta :: TvSubst -> ThetaType -> ThetaType
+substTheta subst theta
+ | isEmptyTvSubst subst = theta
+ | otherwise = map (substPred subst) theta
+
+substPred :: TvSubst -> PredType -> PredType
+substPred subst (IParam n ty) = IParam n (subst_ty subst ty)
+substPred subst (ClassP clas tys) = ClassP clas (map (subst_ty subst) tys)
+
+-- Note that the in_scope set is poked only if we hit a forall
+-- so it may often never be fully computed
+subst_ty subst ty
+ = go ty
+ where
+ go (TyVarTy tv) = substTyVar subst tv
+ go (TyConApp tc tys) = let args = map go tys
+ in args `seqList` TyConApp tc args
+
+ go (PredTy p) = PredTy $! (substPred subst p)
+
+ go (NoteTy (SynNote ty1) ty2) = NoteTy (SynNote $! (go ty1)) $! (go ty2)
+ go (NoteTy (FTVNote _) ty2) = go ty2 -- Discard the free tyvar note
+
+ go (FunTy arg res) = (FunTy $! (go arg)) $! (go res)
+ go (AppTy fun arg) = mkAppTy (go fun) $! (go arg)
+ -- The mkAppTy smart constructor is important
+ -- we might be replacing (a Int), represented with App
+ -- by [Int], represented with TyConApp
+ go (ForAllTy tv ty) = case substTyVarBndr subst tv of
+ (subst', tv') -> ForAllTy tv' $! (subst_ty subst' ty)
+
+substTyVar :: TvSubst -> TyVar -> Type
+substTyVar (TvSubst in_scope env) tv
+ = case (lookupVarEnv env tv) of
+ Nothing -> TyVarTy tv
+ Just ty' -> ty' -- See Note [Apply Once]
+
+substTyVarBndr :: TvSubst -> TyVar -> (TvSubst, TyVar)
+substTyVarBndr subst@(TvSubst in_scope env) old_var
+ | old_var == new_var -- No need to clone
+ -- But we *must* zap any current substitution for the variable.
+ -- For example:
+ -- (\x.e) with id_subst = [x |-> e']
+ -- Here we must simply zap the substitution for x
+ --
+ -- The new_id isn't cloned, but it may have a different type
+ -- etc, so we must return it, not the old id
+ = (TvSubst (in_scope `extendInScopeSet` new_var)
+ (delVarEnv env old_var),
+ new_var)
+
+ | otherwise -- The new binder is in scope so
+ -- we'd better rename it away from the in-scope variables
+ -- Extending the substitution to do this renaming also
+ -- has the (correct) effect of discarding any existing
+ -- substitution for that variable
+ = (TvSubst (in_scope `extendInScopeSet` new_var)
+ (extendVarEnv env old_var (TyVarTy new_var)),
+ new_var)
+ where
+ new_var = uniqAway in_scope old_var
+ -- The uniqAway part makes sure the new variable is not already in scope
\end{code}