-- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
-- for details
+-- | Main functions for manipulating types and type-related things
module Type (
- -- re-exports from TypeRep
- TyThing(..), Type, PredType(..), ThetaType,
- funTyCon,
+ -- Note some of this is just re-exports from TyCon..
- -- Kinds
- Kind, SimpleKind, KindVar,
- kindFunResult, splitKindFunTys, splitKindFunTysN,
-
- liftedTypeKindTyCon, openTypeKindTyCon, unliftedTypeKindTyCon,
- argTypeKindTyCon, ubxTupleKindTyCon,
-
- liftedTypeKind, unliftedTypeKind, openTypeKind,
- argTypeKind, ubxTupleKind,
-
- tySuperKind, coSuperKind,
+ -- * Main data types representing Types
+ -- $type_classification
+
+ -- $representation_types
+ TyThing(..), Type, PredType(..), ThetaType,
- isLiftedTypeKind, isUnliftedTypeKind, isOpenTypeKind,
- isUbxTupleKind, isArgTypeKind, isKind, isTySuperKind,
- isCoSuperKind, isSuperKind, isCoercionKind, isEqPred,
- mkArrowKind, mkArrowKinds,
-
- isSubArgTypeKind, isSubOpenTypeKind, isSubKind, defaultKind, eqKind,
- isSubKindCon,
-
- -- Re-exports from TyCon
- PrimRep(..),
-
- mkTyVarTy, mkTyVarTys, getTyVar, getTyVar_maybe, isTyVarTy,
+ -- ** Constructing and deconstructing types
+ mkTyVarTy, mkTyVarTys, getTyVar, getTyVar_maybe,
mkAppTy, mkAppTys, splitAppTy, splitAppTys,
splitAppTy_maybe, repSplitAppTy_maybe,
mkFunTy, mkFunTys, splitFunTy, splitFunTy_maybe,
splitFunTys, splitFunTysN,
- funResultTy, funArgTy, zipFunTys, isFunTy,
+ funResultTy, funArgTy, zipFunTys,
mkTyConApp, mkTyConTy,
tyConAppTyCon, tyConAppArgs,
splitTyConApp_maybe, splitTyConApp,
- splitNewTyConApp_maybe, splitNewTyConApp,
- repType, typePrimRep, coreView, tcView, kindView, rttiView,
+ mkForAllTy, mkForAllTys, splitForAllTy_maybe, splitForAllTys,
+ applyTy, applyTys, applyTysD, isForAllTy, dropForAlls,
+
+ -- (Newtypes)
+ newTyConInstRhs, carefullySplitNewType_maybe,
+
+ -- (Type families)
+ tyFamInsts, predFamInsts,
- mkForAllTy, mkForAllTys, splitForAllTy_maybe, splitForAllTys,
- applyTy, applyTys, isForAllTy, dropForAlls,
+ -- (Source types)
+ mkPredTy, mkPredTys, mkFamilyTyConApp, isEqPred,
- -- Source types
- predTypeRep, mkPredTy, mkPredTys, pprSourceTyCon, mkFamilyTyConApp,
+ -- ** Common type constructors
+ funTyCon,
- -- Newtypes
- newTyConInstRhs,
+ -- ** Predicates on types
+ isTyVarTy, isFunTy,
- -- Lifting and boxity
+ -- (Lifting and boxity)
isUnLiftedType, isUnboxedTupleType, isAlgType, isClosedAlgType,
isPrimitiveType, isStrictType, isStrictPred,
- -- Free variables
- tyVarsOfType, tyVarsOfTypes, tyVarsOfPred, tyVarsOfTheta,
- typeKind, addFreeTyVars,
+ -- * Main data types representing Kinds
+ -- $kind_subtyping
+ Kind, SimpleKind, KindVar,
+
+ -- ** Common Kinds and SuperKinds
+ liftedTypeKind, unliftedTypeKind, openTypeKind,
+ argTypeKind, ubxTupleKind,
+
+ tySuperKind, coSuperKind,
- -- Type families
- tyFamInsts,
+ -- ** Common Kind type constructors
+ liftedTypeKindTyCon, openTypeKindTyCon, unliftedTypeKindTyCon,
+ argTypeKindTyCon, ubxTupleKindTyCon,
+
+ -- * Type free variables
+ tyVarsOfType, tyVarsOfTypes, tyVarsOfPred, tyVarsOfTheta,
+ expandTypeSynonyms,
- -- Tidying up for printing
+ -- * Tidying type related things up for printing
tidyType, tidyTypes,
tidyOpenType, tidyOpenTypes,
tidyTyVarBndr, tidyFreeTyVars,
tidyTopType, tidyPred,
tidyKind,
- -- Comparison
- coreEqType, tcEqType, tcEqTypes, tcCmpType, tcCmpTypes,
- tcEqPred, tcCmpPred, tcEqTypeX, tcPartOfType, tcPartOfPred,
+ -- * Type comparison
+ coreEqType, coreEqType2,
+ tcEqType, tcEqTypes, tcCmpType, tcCmpTypes,
+ tcEqPred, tcEqPredX, tcCmpPred, tcEqTypeX, tcPartOfType, tcPartOfPred,
- -- Seq
+ -- * Forcing evaluation of types
seqType, seqTypes,
- -- Type substitutions
- TvSubstEnv, emptyTvSubstEnv, -- Representation widely visible
- TvSubst(..), emptyTvSubst, -- Representation visible to a few friends
+ -- * Other views onto Types
+ coreView, tcView, kindView,
+
+ repType,
+
+ -- * Type representation for the code generator
+ PrimRep(..),
+
+ typePrimRep, predTypeRep,
+
+ -- * Main type substitution data types
+ TvSubstEnv, -- Representation widely visible
+ TvSubst(..), -- Representation visible to a few friends
+
+ -- ** Manipulating type substitutions
+ emptyTvSubstEnv, emptyTvSubst,
+
mkTvSubst, mkOpenTvSubst, zipOpenTvSubst, zipTopTvSubst, mkTopTvSubst, notElemTvSubst,
- getTvSubstEnv, setTvSubstEnv, getTvInScope, extendTvInScope,
+ getTvSubstEnv, setTvSubstEnv, zapTvSubstEnv, getTvInScope,
+ extendTvInScope, extendTvInScopeList,
extendTvSubst, extendTvSubstList, isInScope, composeTvSubst, zipTyEnv,
isEmptyTvSubst,
- -- Performing substitution on types
- substTy, substTys, substTyWith, substTheta,
+ -- ** Performing substitution on types
+ substTy, substTys, substTyWith, substTysWith, substTheta,
substPred, substTyVar, substTyVars, substTyVarBndr, deShadowTy, lookupTyVar,
- -- Pretty-printing
+ -- * Pretty-printing
pprType, pprParendType, pprTypeApp, pprTyThingCategory, pprTyThing, pprForAll,
- pprPred, pprTheta, pprThetaArrow, pprClassPred, pprKind, pprParendKind
+ pprPred, pprEqPred, pprTheta, pprThetaArrow, pprClassPred, pprKind, pprParendKind,
+
+ pprSourceTyCon
) where
#include "HsVersions.h"
import Name
import Class
-import PrelNames
import TyCon
-- others
import StaticFlags
import Util
import Outputable
-import UniqSet
+import FastString
import Data.List
import Data.Maybe ( isJust )
\end{code}
+\begin{code}
+-- $type_classification
+-- #type_classification#
+--
+-- Types are one of:
+--
+-- [Unboxed] Iff its representation is other than a pointer
+-- Unboxed types are also unlifted.
+--
+-- [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.
+-- Only lifted types may be unified with a type variable.
+--
+-- [Algebraic] Iff it is 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. This is /not/ the same as
+-- lifted types, because we also include unboxed
+-- tuples in this classification.
+--
+-- [Data] Iff it is a type declared with @data@, or a boxed tuple.
+--
+-- [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: for example, @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.
+--
+-- Some examples of type classifications that may make this a bit clearer are:
+--
+-- @
+-- 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
+-- @
+
+-- $representation_types
+-- A /source type/ is a type that is a separate type as far as the type checker is
+-- concerned, but which has a more low-level representation as far as Core-to-Core
+-- passes and the rest of the back end is concerned. Notably, 'PredTy's are removed
+-- from the representation type while they do exist in the source types.
+--
+-- You don't normally have to worry about this, as the utility functions in
+-- this module will automatically convert a source into a representation type
+-- if they are spotted, to the best of it's abilities. If you don't want this
+-- to happen, use the equivalent functions from the "TcType" module.
+\end{code}
%************************************************************************
%* *
%* *
%************************************************************************
-In Core, we "look through" non-recursive newtypes and PredTypes.
-
\begin{code}
{-# INLINE coreView #-}
coreView :: Type -> Maybe Type
--- Strips off the *top layer only* of a type to give
+-- ^ In Core, we \"look through\" non-recursive newtypes and 'PredTypes': this
+-- function tries to obtain a different view of the supplied type given this
+--
+-- Strips off the /top layer only/ of a type to give
-- its underlying representation type.
-- Returns Nothing if there is nothing to look through.
--
--- In the case of newtypes, it returns
--- *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
+-- In the case of @newtype@s, it returns one of:
+--
+-- 1) A vanilla 'TyConApp' (recursive newtype, or non-saturated)
+--
+-- 2) The newtype representation (otherwise), meaning the
+-- type written in the RHS of the newtype declaration,
+-- which may itself be a newtype
+--
+-- For example, with:
+--
+-- > newtype R = MkR S
+-- > newtype S = MkS T
+-- > newtype T = MkT (T -> T)
+--
+-- 'expandNewTcApp' on:
--
--- 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)
+-- * @R@ gives @Just S@
+-- * @S@ gives @Just T@
+-- * @T@ gives @Nothing@ (no expansion)
-- 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)
| isEqPred p = Nothing
| otherwise = Just (predTypeRep p)
-----------------------------------------------
{-# INLINE tcView #-}
tcView :: Type -> Maybe Type
--- Same, but for the type checker, which just looks through synonyms
-tcView (NoteTy _ ty) = Just ty
+-- ^ Similar to 'coreView', but for the type checker, which just looks through synonyms
tcView (TyConApp tc tys) | Just (tenv, rhs, tys') <- tcExpandTyCon_maybe tc tys
= Just (mkAppTys (substTy (mkTopTvSubst tenv) rhs) tys')
tcView _ = Nothing
-----------------------------------------------
-rttiView :: Type -> Type
--- Same, but for the RTTI system, which cannot deal with predicates nor polymorphism
-rttiView (ForAllTy _ ty) = rttiView ty
-rttiView (NoteTy _ ty) = rttiView ty
-rttiView (FunTy PredTy{} ty) = rttiView ty
-rttiView (FunTy NoteTy{} ty) = rttiView ty
-rttiView ty@TyConApp{} | Just ty' <- coreView ty
- = rttiView ty'
-rttiView (TyConApp tc tys) = mkTyConApp tc (map rttiView tys)
-rttiView ty = ty
+expandTypeSynonyms :: Type -> Type
+-- ^ Expand out all type synonyms. Actually, it'd suffice to expand out
+-- just the ones that discard type variables (e.g. type Funny a = Int)
+-- But we don't know which those are currently, so we just expand all.
+expandTypeSynonyms ty
+ = go ty
+ where
+ go (TyConApp tc tys)
+ | Just (tenv, rhs, tys') <- tcExpandTyCon_maybe tc tys
+ = go (mkAppTys (substTy (mkTopTvSubst tenv) rhs) tys')
+ | otherwise
+ = TyConApp tc (map go tys)
+ go (TyVarTy tv) = TyVarTy tv
+ go (AppTy t1 t2) = AppTy (go t1) (go t2)
+ go (FunTy t1 t2) = FunTy (go t1) (go t2)
+ go (ForAllTy tv t) = ForAllTy tv (go t)
+ go (PredTy p) = PredTy (go_pred p)
+
+ go_pred (ClassP c ts) = ClassP c (map go ts)
+ go_pred (IParam ip t) = IParam ip (go t)
+ go_pred (EqPred t1 t2) = EqPred (go t1) (go t2)
-----------------------------------------------
{-# INLINE kindView #-}
kindView :: Kind -> Maybe Kind
--- C.f. coreView, tcView
+-- ^ Similar to 'coreView' or 'tcView', but works on 'Kind's
+
-- For the moment, we don't even handle synonyms in kinds
-kindView (NoteTy _ k) = Just k
kindView _ = Nothing
\end{code}
mkTyVarTys :: [TyVar] -> [Type]
mkTyVarTys = map mkTyVarTy -- a common use of mkTyVarTy
+-- | Attempts to obtain the type variable underlying a 'Type', and panics with the
+-- given message if this is not a type variable type. See also 'getTyVar_maybe'
getTyVar :: String -> Type -> TyVar
getTyVar msg ty = case getTyVar_maybe ty of
Just tv -> tv
isTyVarTy :: Type -> Bool
isTyVarTy ty = isJust (getTyVar_maybe ty)
+-- | Attempts to obtain the type variable underlying a 'Type'
getTyVar_maybe :: Type -> Maybe TyVar
getTyVar_maybe ty | Just ty' <- coreView ty = getTyVar_maybe ty'
getTyVar_maybe (TyVarTy tv) = Just tv
invariant: use it.
\begin{code}
+-- | Applies a type to another, as in e.g. @k a@
mkAppTy :: Type -> Type -> Type
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 _ = AppTy orig_ty1 orig_ty2
-- Note that the TyConApp could be an
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)
-- mkTyConApp: see notes with mkAppTy
mk_app _ = foldl AppTy orig_ty1 orig_tys2
-------------
splitAppTy_maybe :: Type -> Maybe (Type, Type)
+-- ^ Attempt to take a type application apart, whether it is a
+-- function, type constructor, or plain type application. Note
+-- that type family applications are NEVER unsaturated by this!
splitAppTy_maybe ty | Just ty' <- coreView ty
= splitAppTy_maybe ty'
splitAppTy_maybe ty = repSplitAppTy_maybe ty
-------------
repSplitAppTy_maybe :: Type -> Maybe (Type,Type)
--- Does the AppTy split, but assumes that any view stuff is already done
+-- ^ Does the AppTy split as in 'splitAppTy_maybe', but assumes that
+-- any Core view stuff is already done
repSplitAppTy_maybe (FunTy ty1 ty2) = Just (TyConApp funTyCon [ty1], ty2)
repSplitAppTy_maybe (AppTy ty1 ty2) = Just (ty1, ty2)
repSplitAppTy_maybe (TyConApp tc tys)
- | not (isOpenSynTyCon tc) || length tys > tyConArity tc
+ | isDecomposableTyCon tc || length tys > tyConArity tc
= case snocView tys of -- never create unsaturated type family apps
Just (tys', ty') -> Just (TyConApp tc tys', ty')
Nothing -> Nothing
repSplitAppTy_maybe _other = Nothing
-------------
splitAppTy :: Type -> (Type, Type)
+-- ^ Attempts to take a type application apart, as in 'splitAppTy_maybe',
+-- and panics if this is not possible
splitAppTy ty = case splitAppTy_maybe ty of
Just pr -> pr
Nothing -> panic "splitAppTy"
-------------
splitAppTys :: Type -> (Type, [Type])
+-- ^ Recursively splits a type as far as is possible, leaving a residual
+-- type being applied to and the type arguments applied to it. Never fails,
+-- even if that means returning an empty list of type applications.
splitAppTys ty = split ty ty []
where
split orig_ty ty args | Just ty' <- coreView ty = split orig_ty ty' args
split _ (AppTy ty arg) args = split ty ty (arg:args)
split _ (TyConApp tc tc_args) args
= let -- keep type families saturated
- n | isOpenSynTyCon tc = tyConArity tc
- | otherwise = 0
- (tc_args1, tc_args2) = splitAt n tc_args
+ n | isDecomposableTyCon tc = 0
+ | otherwise = tyConArity tc
+ (tc_args1, tc_args2) = splitAt n tc_args
in
(TyConApp tc tc_args1, tc_args2 ++ args)
split _ (FunTy ty1 ty2) args = ASSERT( null args )
\begin{code}
mkFunTy :: Type -> Type -> Type
-mkFunTy (PredTy (EqPred ty1 ty2)) res = mkForAllTy (mkWildCoVar (PredTy (EqPred ty1 ty2))) res
-mkFunTy arg res = FunTy arg res
+-- ^ Creates a function type from the given argument and result type
+mkFunTy arg@(PredTy (EqPred {})) res = ForAllTy (mkWildCoVar arg) res
+mkFunTy arg res = FunTy arg res
mkFunTys :: [Type] -> Type -> Type
mkFunTys tys ty = foldr mkFunTy ty tys
isFunTy ty = isJust (splitFunTy_maybe ty)
splitFunTy :: Type -> (Type, Type)
+-- ^ Attempts to extract the argument and result types from a type, and
+-- panics if that is not possible. See also 'splitFunTy_maybe'
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)
+-- ^ Attempts to extract the argument and result types from a type
splitFunTy_maybe ty | Just ty' <- coreView ty = splitFunTy_maybe ty'
splitFunTy_maybe (FunTy arg res) = Just (arg, res)
splitFunTy_maybe _ = Nothing
split args orig_ty _ = (reverse args, orig_ty)
splitFunTysN :: Int -> Type -> ([Type], Type)
--- Split off exactly n arg tys
+-- ^ Split off exactly the given number argument types, and panics if that is not possible
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)
+-- | Splits off argument types from the given type and associating
+-- them with the things in the input list from left to right. The
+-- final result type is returned, along with the resulting pairs of
+-- objects and types, albeit with the list of pairs in reverse order.
+-- Panics if there are not enough argument types for the input list.
+zipFunTys :: Outputable a => [a] -> Type -> ([(a, Type)], Type)
zipFunTys orig_xs orig_ty = split [] orig_xs orig_ty orig_ty
where
split acc [] nty _ = (reverse acc, nty)
split _ _ _ _ = pprPanic "zipFunTys" (ppr orig_xs <+> ppr orig_ty)
funResultTy :: Type -> Type
+-- ^ Extract the function result type and panic if that is not possible
funResultTy ty | Just ty' <- coreView ty = funResultTy ty'
funResultTy (FunTy _arg res) = res
funResultTy ty = pprPanic "funResultTy" (ppr ty)
funArgTy :: Type -> Type
+-- ^ Extract the function argument type and panic if that is not possible
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}
+-- | A key function: builds a 'TyConApp' or 'FunTy' as apppropriate to its arguments.
+-- Applies its arguments to the constructor from left to right
mkTyConApp :: TyCon -> [Type] -> Type
mkTyConApp tycon tys
| isFunTyCon tycon, [ty1,ty2] <- tys
| otherwise
= TyConApp tycon tys
+-- | Create the plain type constructor type which has been applied to no type arguments at all.
mkTyConTy :: TyCon -> Type
mkTyConTy tycon = mkTyConApp tycon []
-- mean a distinct type, but all other type-constructor applications
-- including functions are returned as Just ..
+-- | The same as @fst . splitTyConApp@
tyConAppTyCon :: Type -> TyCon
tyConAppTyCon ty = fst (splitTyConApp ty)
+-- | The same as @snd . splitTyConApp@
tyConAppArgs :: Type -> [Type]
tyConAppArgs ty = snd (splitTyConApp ty)
+-- | Attempts to tease a type apart into a type constructor and the application
+-- of a number of arguments to that constructor. Panics if that is not possible.
+-- See also 'splitTyConApp_maybe'
splitTyConApp :: Type -> (TyCon, [Type])
splitTyConApp ty = case splitTyConApp_maybe ty of
Just stuff -> stuff
Nothing -> pprPanic "splitTyConApp" (ppr ty)
+-- | Attempts to tease a type apart into a type constructor and the application
+-- of a number of arguments to that constructor
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 _ = Nothing
--- Sometimes we do NOT want to look throught a newtype. When case matching
--- on a newtype we want a convenient way to access the arguments of a newty
--- constructor so as to properly form a coercion.
-splitNewTyConApp :: Type -> (TyCon, [Type])
-splitNewTyConApp ty = case splitNewTyConApp_maybe ty of
- Just stuff -> stuff
- Nothing -> pprPanic "splitNewTyConApp" (ppr ty)
-splitNewTyConApp_maybe :: Type -> Maybe (TyCon, [Type])
-splitNewTyConApp_maybe ty | Just ty' <- tcView ty = splitNewTyConApp_maybe ty'
-splitNewTyConApp_maybe (TyConApp tc tys) = Just (tc, tys)
-splitNewTyConApp_maybe (FunTy arg res) = Just (funTyCon, [arg,res])
-splitNewTyConApp_maybe _ = Nothing
-
newTyConInstRhs :: TyCon -> [Type] -> Type
--- Unwrap one 'layer' of newtype
--- Use the eta'd version if possible
+-- ^ Unwrap one 'layer' of newtype on a type constructor and its arguments, using an
+-- eta-reduced version of the @newtype@ if possible
newTyConInstRhs tycon tys
= ASSERT2( equalLength tvs tys1, ppr tycon $$ ppr tys $$ ppr tvs )
mkAppTys (substTyWith tvs tys1 ty) tys2
Representation types
~~~~~~~~~~~~~~~~~~~~
-repType looks through
- (a) for-alls, and
- (b) synonyms
- (c) predicates
- (d) usage annotations
- (e) all newtypes, including recursive ones, but not newtype families
-It's useful in the back end.
\begin{code}
+-- | Looks through:
+--
+-- 1. For-alls
+-- 2. Synonyms
+-- 3. Predicates
+-- 4. All newtypes, including recursive ones, but not newtype families
+--
+-- It's useful in the back end of the compiler.
repType :: Type -> Type
-- Only applied to types of kind *; hence tycons are saturated
repType ty
go rec_nts (ForAllTy _ ty) -- Look through foralls
= go rec_nts ty
- go rec_nts ty@(TyConApp tc tys) -- Expand newtypes
- | Just _co_con <- newTyConCo_maybe tc -- See Note [Expanding newtypes]
- = if tc `elem` rec_nts -- in Type.lhs
- then ty
- else go rec_nts' nt_rhs
- where
- nt_rhs = newTyConInstRhs tc tys
- rec_nts' | isRecursiveTyCon tc = tc:rec_nts
- | otherwise = rec_nts
+ go rec_nts (TyConApp tc tys) -- Expand newtypes
+ | Just (rec_nts', ty') <- carefullySplitNewType_maybe rec_nts tc tys
+ = go rec_nts' ty'
go _ ty = ty
+carefullySplitNewType_maybe :: [TyCon] -> TyCon -> [Type] -> Maybe ([TyCon],Type)
+-- Return the representation of a newtype, unless
+-- we've seen it already: see Note [Expanding newtypes]
+carefullySplitNewType_maybe rec_nts tc tys
+ | isNewTyCon tc
+ , not (tc `elem` rec_nts) = Just (rec_nts', newTyConInstRhs tc tys)
+ | otherwise = Nothing
+ where
+ rec_nts' | isRecursiveTyCon tc = tc:rec_nts
+ | otherwise = rec_nts
+
+
-- ToDo: this could be moved to the code generator, using splitTyConApp instead
-- of inspecting the type directly.
+
+-- | Discovers the primitive representation of a more abstract 'Type'
typePrimRep :: Type -> PrimRep
typePrimRep ty = case repType ty of
TyConApp tc _ -> tyConPrimRep tc
\begin{code}
mkForAllTy :: TyVar -> Type -> Type
mkForAllTy tyvar ty
- = mkForAllTys [tyvar] ty
+ = ForAllTy tyvar ty
+-- | Wraps foralls over the type using the provided 'TyVar's from left to right
mkForAllTys :: [TyVar] -> Type -> Type
mkForAllTys tyvars ty = foldr ForAllTy ty tyvars
isForAllTy :: Type -> Bool
-isForAllTy (NoteTy _ ty) = isForAllTy ty
isForAllTy (ForAllTy _ _) = True
isForAllTy _ = False
+-- | Attempts to take a forall type apart, returning the bound type variable
+-- and the remainder of the type
splitForAllTy_maybe :: Type -> Maybe (TyVar, Type)
splitForAllTy_maybe ty = splitFAT_m ty
where
splitFAT_m (ForAllTy tyvar ty) = Just(tyvar, ty)
splitFAT_m _ = Nothing
+-- | Attempts to take a forall type apart, returning all the immediate such bound
+-- type variables and the remainder of the type. Always suceeds, even if that means
+-- returning an empty list of 'TyVar's
splitForAllTys :: Type -> ([TyVar], Type)
splitForAllTys ty = split ty ty []
where
split _ (ForAllTy tv ty) tvs = split ty ty (tv:tvs)
split orig_ty _ tvs = (reverse tvs, orig_ty)
+-- | Equivalent to @snd . splitForAllTys@
dropForAlls :: Type -> Type
dropForAlls ty = snd (splitForAllTys 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}
+-- | Instantiate a forall type with one or more type arguments.
+-- Used when we have a polymorphic function applied to type args:
+--
+-- > f t1 t2
+--
+-- We use @applyTys type-of-f [t1,t2]@ to compute the type of the expression.
+-- Panics if no application is possible.
applyTy :: Type -> Type -> Type
applyTy ty arg | Just ty' <- coreView ty = applyTy ty' arg
applyTy (ForAllTy tv ty) arg = substTyWith [tv] [arg] ty
applyTy _ _ = panic "applyTy"
applyTys :: Type -> [Type] -> Type
--- 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 function is interesting because:
+--
+-- 1. The function may have more for-alls than there are args
+--
+-- 2. Less obviously, it may have fewer for-alls
+--
+-- For case 2. 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 ()
+--
+-- > 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
+applyTys ty args = applyTysD empty ty args
+
+applyTysD :: SDoc -> Type -> [Type] -> Type -- Debug version
+applyTysD _ orig_fun_ty [] = orig_fun_ty
+applyTysD doc 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)
+ = ASSERT2( n_tvs > 0, doc $$ ppr orig_fun_ty ) -- Zero case gives infnite loop!
+ applyTysD doc (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
%* *
%************************************************************************
-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.
-
Source types are always lifted.
The key function is predTypeRep which gives the representation of a source type:
mkPredTys :: ThetaType -> [Type]
mkPredTys preds = map PredTy preds
+isEqPred :: PredType -> Bool
+isEqPred (EqPred _ _) = True
+isEqPred _ = False
+
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
+-- ^ Convert a 'PredType' to its representation type. However, it 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
predTypeRep (EqPred ty1 ty2) = pprPanic "predTypeRep" (ppr (EqPred ty1 ty2))
mkFamilyTyConApp :: TyCon -> [Type] -> Type
--- Given a family instance TyCon and its arg types, return the
--- corresponding family type. E.g.
--- data family T a
--- data instance T (Maybe b) = MkT b -- Instance tycon :RTL
--- Then
--- mkFamilyTyConApp :RTL Int = T (Maybe Int)
+-- ^ Given a family instance TyCon and its arg types, return the
+-- corresponding family type. E.g:
+--
+-- > data family T a
+-- > data instance T (Maybe b) = MkT b
+--
+-- Where the instance tycon is :RTL, so:
+--
+-- > mkFamilyTyConApp :RTL Int = T (Maybe Int)
mkFamilyTyConApp tc tys
| Just (fam_tc, fam_tys) <- tyConFamInst_maybe tc
, let fam_subst = zipTopTvSubst (tyConTyVars tc) tys
| otherwise
= mkTyConApp tc tys
--- Pretty prints a tycon, using the family instance in case of a
--- representation tycon. For example
--- e.g. data T [a] = ...
--- In that case we want to print `T [a]', where T is the family TyCon
+-- | Pretty prints a 'TyCon', using the family instance in case of a
+-- representation tycon. For example:
+--
+-- > data T [a] = ...
+--
+-- In that case we want to print @T [a]@, where @T@ is the family 'TyCon'
pprSourceTyCon :: TyCon -> SDoc
pprSourceTyCon tycon
| Just (fam_tc, tys) <- tyConFamInst_maybe tycon
%************************************************************************
%* *
-\subsection{Kinds and free variables}
+ The free variables of a type
%* *
%************************************************************************
----------------------------------------------------------------------
- Finding the kind of a type
- ~~~~~~~~~~~~~~~~~~~~~~~~~~
-\begin{code}
-typeKind :: Type -> Kind
-typeKind (TyConApp tycon tys) = ASSERT( not (isCoercionTyCon tycon) )
- -- We should be looking for the coercion kind,
- -- not the type kind
- foldr (\_ k -> kindFunResult k) (tyConKind tycon) tys
-typeKind (NoteTy _ ty) = typeKind ty
-typeKind (PredTy pred) = predKind pred
-typeKind (AppTy fun _) = kindFunResult (typeKind fun)
-typeKind (ForAllTy _ ty) = typeKind ty
-typeKind (TyVarTy tyvar) = tyVarKind tyvar
-typeKind (FunTy _arg res)
- -- Hack alert. The kind of (Int -> Int#) is liftedTypeKind (*),
- -- not unliftedTypKind (#)
- -- The only things that can be after a function arrow are
- -- (a) types (of kind openTypeKind or its sub-kinds)
- -- (b) kinds (of super-kind TY) (e.g. * -> (* -> *))
- | isTySuperKind k = k
- | otherwise = ASSERT( isSubOpenTypeKind k) liftedTypeKind
- where
- k = typeKind res
-
-predKind :: PredType -> Kind
-predKind (EqPred {}) = coSuperKind -- A coercion kind!
-predKind (ClassP {}) = liftedTypeKind -- Class and implicitPredicates are
-predKind (IParam {}) = liftedTypeKind -- always represented by lifted types
-\end{code}
-
-
----------------------------------------------------------------------
- Free variables of a type
- ~~~~~~~~~~~~~~~~~~~~~~~~
\begin{code}
tyVarsOfType :: Type -> TyVarSet
--- NB: for type synonyms tyVarsOfType does *not* expand the synonym
+-- ^ NB: for type synonyms tyVarsOfType does /not/ expand the synonym
tyVarsOfType (TyVarTy tv) = unitVarSet tv
tyVarsOfType (TyConApp _ tys) = tyVarsOfTypes tys
-tyVarsOfType (NoteTy (FTVNote tvs) _) = tvs
tyVarsOfType (PredTy sty) = tyVarsOfPred sty
tyVarsOfType (FunTy arg res) = tyVarsOfType arg `unionVarSet` tyVarsOfType res
tyVarsOfType (AppTy fun arg) = tyVarsOfType fun `unionVarSet` tyVarsOfType arg
tyVarsOfTheta :: ThetaType -> TyVarSet
tyVarsOfTheta = foldr (unionVarSet . tyVarsOfPred) emptyVarSet
-
--- 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}
%* *
%************************************************************************
-Type family instances occuring in a type after expanding synonyms.
-
\begin{code}
+-- | Finds type family instances occuring in a type after expanding synonyms.
tyFamInsts :: Type -> [(TyCon, [Type])]
tyFamInsts ty
| Just exp_ty <- tcView ty = tyFamInsts exp_ty
tyFamInsts (FunTy ty1 ty2) = tyFamInsts ty1 ++ tyFamInsts ty2
tyFamInsts (AppTy ty1 ty2) = tyFamInsts ty1 ++ tyFamInsts ty2
tyFamInsts (ForAllTy _ ty) = tyFamInsts ty
+tyFamInsts (PredTy pty) = predFamInsts pty
+
+-- | Finds type family instances occuring in a predicate type after expanding
+-- synonyms.
+predFamInsts :: PredType -> [(TyCon, [Type])]
+predFamInsts (ClassP _cla tys) = concat (map tyFamInsts tys)
+predFamInsts (IParam _ ty) = tyFamInsts ty
+predFamInsts (EqPred ty1 ty2) = tyFamInsts ty1 ++ tyFamInsts ty2
\end{code}
%* *
%************************************************************************
-tidyTy 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.
-
\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
name = tyVarName tyvar
tidyFreeTyVars :: TidyEnv -> TyVarSet -> TidyEnv
--- Add the free tyvars to the env in tidy form,
+-- ^ 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 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
+-- ^ 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
Just tv' -> TyVarTy tv'
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)
where
(envp, tvp) = tidyTyVarBndr env tv
- go_note note@(FTVNote _ftvs) = note -- No need to tidy the free tyvars
-
tidyTypes :: TidyEnv -> [Type] -> [Type]
tidyTypes env tys = map (tidyType env) tys
\end{code}
-@tidyOpenType@ grabs the free type variables, tidies them
-and then uses @tidyType@ to work over the type itself
-
\begin{code}
+-- | 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)
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
\end{code}
%************************************************************************
\begin{code}
+-- | See "Type#type_classification" for what an unlifted type is
isUnLiftedType :: Type -> Bool
-- isUnLiftedType returns True for forall'd unlifted types:
-- x :: forall a. Int#
Just (tc, _ty_args) -> isUnboxedTupleTyCon tc
_ -> False
--- Should only be applied to *types*; hence the assert
+-- | See "Type#type_classification" for what an algebraic type is.
+-- Should only be applied to /types/, as opposed to e.g. partially
+-- saturated type constructors
isAlgType :: Type -> Bool
isAlgType ty
= case splitTyConApp_maybe ty of
isAlgTyCon tc
_other -> False
--- Should only be applied to *types*; hence the assert
+-- | See "Type#type_classification" for what an algebraic type is.
+-- Should only be applied to /types/, as opposed to e.g. partially
+-- saturated type constructors. Closed type constructors are those
+-- with a fixed right hand side, as opposed to e.g. associated types
isClosedAlgType :: Type -> Bool
isClosedAlgType ty
= case splitTyConApp_maybe ty of
_other -> False
\end{code}
-@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}
+-- | Computes whether an argument (or let right hand side) should
+-- be computed strictly or lazily, based only on its type.
+-- Works just like 'isUnLiftedType', except that it has a special case
+-- for dictionaries (i.e. does not work purely on representation types)
+
+-- Since it takes account of class 'PredType's, 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.
isStrictType :: Type -> Bool
isStrictType (PredTy pred) = isStrictPred pred
isStrictType ty | Just ty' <- coreView ty = isStrictType ty'
isStrictType (TyConApp tc _) = isUnLiftedTyCon tc
isStrictType _ = 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.)
isStrictPred :: PredType -> Bool
isStrictPred (ClassP clas _) = opt_DictsStrict && not (isNewTyCon (classTyCon clas))
isStrictPred _ = 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.
+-- ^ Returns true of 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
%************************************************************************
%* *
-\subsection{Sequencing on types
+\subsection{Sequencing on types}
%* *
%************************************************************************
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 [] = ()
seqTypes (ty:tys) = seqType ty `seq` seqTypes tys
-seqNote :: TyNote -> ()
-seqNote (FTVNote set) = sizeUniqSet set `seq` ()
-
seqPred :: PredType -> ()
seqPred (ClassP c tys) = c `seq` seqTypes tys
seqPred (IParam n ty) = n `seq` seqType ty
See Note [Newtype eta] in TyCon.lhs
\begin{code}
+-- | Type equality test for Core types (i.e. ignores predicate-types, synonyms etc.)
coreEqType :: Type -> Type -> Bool
-coreEqType t1 t2
- = eq rn_env t1 t2
+coreEqType t1 t2 = coreEqType2 rn_env t1 t2
where
rn_env = mkRnEnv2 (mkInScopeSet (tyVarsOfType t1 `unionVarSet` tyVarsOfType t2))
+coreEqType2 :: RnEnv2 -> Type -> Type -> Bool
+coreEqType2 rn_env t1 t2
+ = eq rn_env t1 t2
+ where
eq env (TyVarTy tv1) (TyVarTy tv2) = rnOccL env tv1 == rnOccR env tv2
eq env (ForAllTy tv1 t1) (ForAllTy tv2 t2) = eq (rnBndr2 env tv1 tv2) t1 t2
eq env (AppTy s1 t1) (AppTy s2 t2) = eq env s1 s2 && eq env t1 t2
%* *
%************************************************************************
-Note that
- tcEqType, tcCmpType
-do *not* look through newtypes, PredTypes
-
\begin{code}
tcEqType :: Type -> Type -> Bool
+-- ^ Type equality on source types. Does not look through @newtypes@ or
+-- 'PredType's, but it does look through type synonyms.
tcEqType t1 t2 = isEqual $ cmpType t1 t2
tcEqTypes :: [Type] -> [Type] -> Bool
tcEqTypes tys1 tys2 = isEqual $ cmpTypes tys1 tys2
tcCmpType :: Type -> Type -> Ordering
+-- ^ Type ordering on source types. Does not look through @newtypes@ or
+-- 'PredType's, but it does look through type synonyms.
tcCmpType t1 t2 = cmpType t1 t2
tcCmpTypes :: [Type] -> [Type] -> Ordering
tcEqPred :: PredType -> PredType -> Bool
tcEqPred p1 p2 = isEqual $ cmpPred p1 p2
+tcEqPredX :: RnEnv2 -> PredType -> PredType -> Bool
+tcEqPredX env p1 p2 = isEqual $ cmpPredX env p1 p2
+
tcCmpPred :: PredType -> PredType -> Ordering
tcCmpPred p1 p2 = cmpPred p1 p2
tcEqTypeX env t1 t2 = isEqual $ cmpTypeX env t1 t2
\end{code}
-Checks whether the second argument is a subterm of the first. (We don't care
-about binders, as we are only interested in syntactic subterms.)
-
\begin{code}
+-- | Checks whether the second argument is a subterm of the first. (We don't care
+-- about binders, as we are only interested in syntactic subterms.)
tcPartOfType :: Type -> Type -> Bool
tcPartOfType t1 t2
| tcEqType t1 t2 = True
tcPartOfType t1 (FunTy s2 t2) = tcPartOfType t1 s2 || tcPartOfType t1 t2
tcPartOfType t1 (PredTy p2) = tcPartOfPred t1 p2
tcPartOfType t1 (TyConApp _ ts) = any (tcPartOfType t1) ts
-tcPartOfType t1 (NoteTy _ t2) = tcPartOfType t1 t2
tcPartOfPred :: Type -> PredType -> Bool
tcPartOfPred t1 (IParam _ t2) = tcPartOfType 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 t1 (NoteTy _ t2) = cmpTypeX env t1 t2
-- Deal with the rest: TyVarTy < AppTy < FunTy < TyConApp < ForAllTy < PredTy
cmpTypeX _ (AppTy _ _) (TyVarTy _) = GT
%************************************************************************
\begin{code}
+-- | Type substitution
+--
+-- #tvsubst_invariant#
+-- The following invariants must hold of a 'TvSubst':
+--
+-- 1. The in-scope set is needed /only/ to
+-- guide the generation of fresh uniques
+--
+-- 2. In particular, the /kind/ of the type variables in
+-- the in-scope set is not relevant
+--
+-- 3. The substition is only applied ONCE! This is because
+-- in general such application will not reached a fixed point.
data TvSubst
= TvSubst InScopeSet -- The in-scope type variables
TvSubstEnv -- The substitution itself
Note [Extending the TvSubst]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-The following invariant should hold of a TvSubst
-
- The in-scope set is needed *only* to
- guide the generation of fresh uniques
-
- In particular, the *kind* of the type variables in
- the in-scope set is not relevant
+See #tvsubst_invariant# for the invariants that must hold.
This invariant allows a short-cut when the TvSubstEnv is empty:
if the TvSubstEnv is empty --- i.e. (isEmptyTvSubt subst) holds ---
-------------------------------------------------------------- -}
-
+-- | A substitition of 'Type's for 'TyVar's
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
+
emptyTvSubstEnv :: TvSubstEnv
emptyTvSubstEnv = emptyVarEnv
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
--- Typically, env1 is the refinement to a base substitution env2
+-- ^ @(compose env1 env2)(x)@ is @env1(env2(x))@; i.e. apply @env2@ then @env1@.
+-- It assumes that both are idempotent.
+-- Typically, @env1@ is the refinement to a base substitution @env2@
composeTvSubst in_scope env1 env2
= env1 `plusVarEnv` mapVarEnv (substTy subst1) env2
-- First apply env1 to the range of env2
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
+zapTvSubstEnv :: TvSubst -> TvSubst
+zapTvSubstEnv (TvSubst in_scope _) = TvSubst in_scope emptyVarEnv
+
+extendTvInScope :: TvSubst -> Var -> TvSubst
+extendTvInScope (TvSubst in_scope env) var = TvSubst (extendInScopeSet in_scope var) env
+
+extendTvInScopeList :: TvSubst -> [Var] -> TvSubst
+extendTvInScopeList (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)
-- the types given; but it's just a thunk so with a bit of luck
-- it'll never be evaluated
+-- Note [Generating the in-scope set for a substitution]
+-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+-- If we want to substitute [a -> ty1, b -> ty2] I used to
+-- think it was enough to generate an in-scope set that includes
+-- fv(ty1,ty2). But that's not enough; we really should also take the
+-- free vars of the type we are substituting into! Example:
+-- (forall b. (a,b,x)) [a -> List b]
+-- Then if we use the in-scope set {b}, there is a danger we will rename
+-- the forall'd variable to 'x' by mistake, getting this:
+-- (forall x. (List b, x, x)
+-- Urk! This means looking at all the calls to mkOpenTvSubst....
+
+
+-- | Generates the in-scope set for the 'TvSubst' from the types in the incoming
+-- environment, hence "open"
mkOpenTvSubst :: TvSubstEnv -> TvSubst
mkOpenTvSubst env = TvSubst (mkInScopeSet (tyVarsOfTypes (varEnvElts env))) env
+-- | Generates the in-scope set for the 'TvSubst' from the types in the incoming
+-- environment, hence "open"
zipOpenTvSubst :: [TyVar] -> [Type] -> TvSubst
zipOpenTvSubst tyvars tys
-#ifdef DEBUG
- | length tyvars /= length tys
+ | debugIsOn && (length tyvars /= length tys)
= pprTrace "zipOpenTvSubst" (ppr tyvars $$ ppr tys) emptyTvSubst
| otherwise
-#endif
= 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.
+-- | 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
-#ifdef DEBUG
- | length tyvars /= length tys
+ | debugIsOn && (length tyvars /= length tys)
= pprTrace "zipTopTvSubst" (ppr tyvars $$ ppr tys) emptyTvSubst
| otherwise
-#endif
= TvSubst emptyInScopeSet (zipTyEnv tyvars tys)
zipTyEnv :: [TyVar] -> [Type] -> TvSubstEnv
zipTyEnv tyvars tys
-#ifdef DEBUG
- | length tyvars /= length tys
+ | debugIsOn && (length tyvars /= length tys)
= pprTrace "mkTopTvSubst" (ppr tyvars $$ ppr tys) emptyVarEnv
| otherwise
-#endif
= zip_ty_env tyvars tys emptyVarEnv
-- Later substitutions in the list over-ride earlier ones,
instance Outputable TvSubst where
ppr (TvSubst ins env)
- = brackets $ sep[ ptext SLIT("TvSubst"),
- nest 2 (ptext SLIT("In scope:") <+> ppr ins),
- nest 2 (ptext SLIT("Env:") <+> ppr env) ]
+ = brackets $ sep[ ptext (sLit "TvSubst"),
+ nest 2 (ptext (sLit "In scope:") <+> ppr ins),
+ nest 2 (ptext (sLit "Env:") <+> ppr env) ]
\end{code}
%************************************************************************
%************************************************************************
\begin{code}
+-- | Type substitution making use of an 'TvSubst' that
+-- is assumed to be open, see 'zipOpenTvSubst'
substTyWith :: [TyVar] -> [Type] -> Type -> Type
substTyWith tvs tys = ASSERT( length tvs == length tys )
substTy (zipOpenTvSubst tvs tys)
+-- | Type substitution making use of an 'TvSubst' that
+-- is assumed to be open, see 'zipOpenTvSubst'
+substTysWith :: [TyVar] -> [Type] -> [Type] -> [Type]
+substTysWith tvs tys = ASSERT( length tvs == length tys )
+ substTys (zipOpenTvSubst tvs tys)
+
+-- | Substitute within a 'Type'
substTy :: TvSubst -> Type -> Type
substTy subst ty | isEmptyTvSubst subst = ty
| otherwise = subst_ty subst ty
+-- | Substitute within several 'Type's
substTys :: TvSubst -> [Type] -> [Type]
substTys subst tys | isEmptyTvSubst subst = tys
| otherwise = map (subst_ty subst) tys
+-- | Substitute within a 'ThetaType'
substTheta :: TvSubst -> ThetaType -> ThetaType
substTheta subst theta
| isEmptyTvSubst subst = theta
| otherwise = map (substPred subst) theta
+-- | Substitute within a 'PredType'
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)
substPred subst (EqPred ty1 ty2) = EqPred (subst_ty subst ty1) (subst_ty subst ty2)
-deShadowTy :: TyVarSet -> Type -> Type -- Remove any nested binders mentioning tvs
+-- | Remove any nested binders mentioning the 'TyVar's in the 'TyVarSet'
+deShadowTy :: TyVarSet -> Type -> Type
deShadowTy tvs ty
= subst_ty (mkTvSubst in_scope emptyTvSubstEnv) ty
where
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 (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 (PredTy p) = PredTy $! (substPred subst p)
- 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)
+ 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 subst@(TvSubst _ _) tv
Kinds
~~~~~
-There's a little subtyping at the kind level:
-
- ?
- / \
- / \
- ?? (#)
- / \
- * #
-
-where * [LiftedTypeKind] means boxed type
- # [UnliftedTypeKind] means unboxed type
- (#) [UbxTupleKind] means unboxed tuple
- ?? [ArgTypeKind] is the lub of *,#
- ? [OpenTypeKind] means any type at all
-
-In particular:
-
- error :: forall a:?. String -> a
- (->) :: ?? -> ? -> *
- (\(x::t) -> ...) Here t::?? (i.e. not unboxed tuple)
\begin{code}
+-- $kind_subtyping
+-- #kind_subtyping#
+-- There's a little subtyping at the kind level:
+--
+-- @
+-- ?
+-- \/ \
+-- \/ \
+-- ?? (\#)
+-- \/ \
+-- \* \#
+-- .
+-- Where: \* [LiftedTypeKind] means boxed type
+-- \# [UnliftedTypeKind] means unboxed type
+-- (\#) [UbxTupleKind] means unboxed tuple
+-- ?? [ArgTypeKind] is the lub of {\*, \#}
+-- ? [OpenTypeKind] means any type at all
+-- @
+--
+-- In particular:
+--
+-- > error :: forall a:?. String -> a
+-- > (->) :: ?? -> ? -> \*
+-- > (\\(x::t) -> ...)
+--
+-- Where in the last example @t :: ??@ (i.e. is not an unboxed tuple)
+
type KindVar = TyVar -- invariant: KindVar will always be a
-- TcTyVar with details MetaTv TauTv ...
-- kind var constructors and functions are in TcType
finding the GLB of the two. Since the partial order is a tree, they only
have a glb if one is a sub-kind of the other. In that case, we bind the
less-informative one to the more informative one. Neat, eh?
-
-
-\begin{code}
-
-\end{code}
-
-%************************************************************************
-%* *
- Functions over Kinds
-%* *
-%************************************************************************
-
-\begin{code}
-kindFunResult :: Kind -> Kind
-kindFunResult k = funResultTy k
-
-splitKindFunTys :: Kind -> ([Kind],Kind)
-splitKindFunTys k = splitFunTys k
-
-splitKindFunTysN :: Int -> Kind -> ([Kind],Kind)
-splitKindFunTysN k = splitFunTysN k
-
-isUbxTupleKind, isOpenTypeKind, isArgTypeKind, isUnliftedTypeKind :: Kind -> Bool
-isOpenTypeKindCon, isUbxTupleKindCon, isArgTypeKindCon,
- isUnliftedTypeKindCon, isSubArgTypeKindCon :: TyCon -> Bool
-
-isOpenTypeKindCon tc = tyConUnique tc == openTypeKindTyConKey
-
-isOpenTypeKind (TyConApp tc _) = isOpenTypeKindCon tc
-isOpenTypeKind _ = False
-
-isUbxTupleKindCon tc = tyConUnique tc == ubxTupleKindTyConKey
-
-isUbxTupleKind (TyConApp tc _) = isUbxTupleKindCon tc
-isUbxTupleKind _ = False
-
-isArgTypeKindCon tc = tyConUnique tc == argTypeKindTyConKey
-
-isArgTypeKind (TyConApp tc _) = isArgTypeKindCon tc
-isArgTypeKind _ = False
-
-isUnliftedTypeKindCon tc = tyConUnique tc == unliftedTypeKindTyConKey
-
-isUnliftedTypeKind (TyConApp tc _) = isUnliftedTypeKindCon tc
-isUnliftedTypeKind _ = False
-
-isSubOpenTypeKind :: Kind -> Bool
--- True of any sub-kind of OpenTypeKind (i.e. anything except arrow)
-isSubOpenTypeKind (FunTy k1 k2) = ASSERT2 ( isKind k1, text "isSubOpenTypeKind" <+> ppr k1 <+> text "::" <+> ppr (typeKind k1) )
- ASSERT2 ( isKind k2, text "isSubOpenTypeKind" <+> ppr k2 <+> text "::" <+> ppr (typeKind k2) )
- False
-isSubOpenTypeKind (TyConApp kc []) = ASSERT( isKind (TyConApp kc []) ) True
-isSubOpenTypeKind other = ASSERT( isKind other ) False
- -- This is a conservative answer
- -- It matters in the call to isSubKind in
- -- checkExpectedKind.
-
-isSubArgTypeKindCon kc
- | isUnliftedTypeKindCon kc = True
- | isLiftedTypeKindCon kc = True
- | isArgTypeKindCon kc = True
- | otherwise = False
-
-isSubArgTypeKind :: Kind -> Bool
--- True of any sub-kind of ArgTypeKind
-isSubArgTypeKind (TyConApp kc []) = isSubArgTypeKindCon kc
-isSubArgTypeKind _ = False
-
-isSuperKind :: Type -> Bool
-isSuperKind (TyConApp (skc) []) = isSuperKindTyCon skc
-isSuperKind _ = False
-
-isKind :: Kind -> Bool
-isKind k = isSuperKind (typeKind k)
-
-isSubKind :: Kind -> Kind -> Bool
--- (k1 `isSubKind` k2) checks that k1 <: k2
-isSubKind (TyConApp kc1 []) (TyConApp kc2 []) = kc1 `isSubKindCon` kc2
-isSubKind (FunTy a1 r1) (FunTy a2 r2) = (a2 `isSubKind` a1) && (r1 `isSubKind` r2)
-isSubKind (PredTy (EqPred ty1 ty2)) (PredTy (EqPred ty1' ty2'))
- = ty1 `tcEqType` ty1' && ty2 `tcEqType` ty2'
-isSubKind _ _ = False
-
-eqKind :: Kind -> Kind -> Bool
-eqKind = tcEqType
-
-isSubKindCon :: TyCon -> TyCon -> Bool
--- (kc1 `isSubKindCon` kc2) checks that kc1 <: kc2
-isSubKindCon kc1 kc2
- | isLiftedTypeKindCon kc1 && isLiftedTypeKindCon kc2 = True
- | isUnliftedTypeKindCon kc1 && isUnliftedTypeKindCon kc2 = True
- | isUbxTupleKindCon kc1 && isUbxTupleKindCon kc2 = True
- | isOpenTypeKindCon kc2 = True
- -- we already know kc1 is not a fun, its a TyCon
- | isArgTypeKindCon kc2 && isSubArgTypeKindCon kc1 = True
- | otherwise = False
-
-defaultKind :: Kind -> Kind
--- Used when generalising: default kind '?' and '??' to '*'
---
--- When we generalise, we make generic type variables whose kind is
--- simple (* or *->* etc). So generic type variables (other than
--- built-in constants like 'error') always have simple kinds. This is important;
--- consider
--- f x = True
--- We want f to get type
--- f :: forall (a::*). a -> Bool
--- Not
--- f :: forall (a::??). a -> Bool
--- because that would allow a call like (f 3#) as well as (f True),
---and the calling conventions differ. This defaulting is done in TcMType.zonkTcTyVarBndr.
-defaultKind k
- | isSubOpenTypeKind k = liftedTypeKind
- | isSubArgTypeKind k = liftedTypeKind
- | otherwise = k
-
-isEqPred :: PredType -> Bool
-isEqPred (EqPred _ _) = True
-isEqPred _ = False
-\end{code}
projects / ghc-hetmet.git / blobdiff