-%
-% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
-%
-\section{Unify}
+\begin{code}
+module Unify (
+ -- Matching and unification
+ tcMatchTys, tcMatchTyX, ruleMatchTyX, tcMatchPreds, MatchEnv(..),
-This module contains a unifier and a matcher, both of which
-use an explicit substitution
+ tcUnifyTys,
-\begin{code}
-module Unify ( Subst,
- unifyTysX, unifyTyListsX,
- matchTy, matchTys
- ) where
+ gadtRefineTys, BindFlag(..),
+
+ coreRefineTys, TypeRefinement,
+
+ -- Re-export
+ MaybeErr(..)
+ ) where
-import Var ( GenTyVar, TyVar, tyVarKind )
+#include "HsVersions.h"
+
+import Var ( Var, TyVar, tyVarKind )
import VarEnv
-import VarSet ( varSetElems )
-import Type ( GenType(..), funTyCon, typeKind, tyVarsOfType, hasMoreBoxityInfo,
- splitAppTy_maybe
- )
-import Unique ( Uniquable(..) )
-import Outputable( panic )
-import Util ( snocView )
+import VarSet
+import Kind ( isSubKind )
+import Type ( typeKind, tyVarsOfType, tyVarsOfTypes, tyVarsOfTheta, mkTyVarTys,
+ TvSubstEnv, emptyTvSubstEnv, TvSubst(..), substTy, tcEqTypeX,
+ mkOpenTvSubst, tcView )
+import TypeRep ( Type(..), PredType(..), funTyCon )
+import DataCon ( DataCon, dataConInstResTy )
+import Util ( snocView )
+import ErrUtils ( Message )
+import Outputable
+import Maybes
\end{code}
+
%************************************************************************
%* *
-\subsection{Unification wih a explicit substitution}
+ Matching
%* *
%************************************************************************
-Unify types with an explicit substitution and no monad.
-\begin{code}
-type Subst flexi_tmpl flexi_result
- = ([GenTyVar flexi_tmpl], -- Set of template tyvars
- TyVarEnv (GenType flexi_result)) -- Not necessarily idempotent
-
-unifyTysX :: [GenTyVar flexi] -- Template tyvars
- -> GenType flexi
- -> GenType flexi
- -> Maybe (TyVarEnv (GenType flexi))
-unifyTysX tmpl_tyvars ty1 ty2
- = uTysX ty1 ty2 (\(_,s) -> Just s) (tmpl_tyvars, emptyVarEnv)
-
-unifyTyListsX :: [GenTyVar flexi] -> [GenType flexi] -> [GenType flexi]
- -> Maybe (TyVarEnv (GenType flexi))
-unifyTyListsX tmpl_tyvars tys1 tys2
- = uTyListsX tys1 tys2 (\(_,s) -> Just s) (tmpl_tyvars, emptyVarEnv)
-
-
-uTysX :: GenType flexi
- -> GenType flexi
- -> (Subst flexi flexi -> Maybe result)
- -> Subst flexi flexi
- -> Maybe result
-
-uTysX (NoteTy _ ty1) ty2 k subst = uTysX ty1 ty2 k subst
-uTysX ty1 (NoteTy _ ty2) k subst = uTysX ty1 ty2 k subst
-
- -- Variables; go for uVar
-uTysX (TyVarTy tyvar1) (TyVarTy tyvar2) k subst
- | tyvar1 == tyvar2
- = k subst
-uTysX (TyVarTy tyvar1) ty2 k subst@(tmpls,_)
- | tyvar1 `elem` tmpls
- = uVarX tyvar1 ty2 k subst
-uTysX ty1 (TyVarTy tyvar2) k subst@(tmpls,_)
- | tyvar2 `elem` tmpls
- = uVarX tyvar2 ty1 k subst
-
- -- Functions; just check the two parts
-uTysX (FunTy fun1 arg1) (FunTy fun2 arg2) k subst
- = uTysX fun1 fun2 (uTysX arg1 arg2 k) subst
-
- -- Type constructors must match
-uTysX (TyConApp con1 tys1) (TyConApp con2 tys2) k subst
- | (con1 == con2 && length tys1 == length tys2)
- = uTyListsX tys1 tys2 k subst
+Matching is much tricker than you might think.
- -- Applications need a bit of care!
- -- They can match FunTy and TyConApp, so use splitAppTy_maybe
- -- NB: we've already dealt with type variables and Notes,
- -- so if one type is an App the other one jolly well better be too
-uTysX (AppTy s1 t1) ty2 k subst
- = case splitAppTy_maybe ty2 of
- Just (s2, t2) -> uTysX s1 s2 (uTysX t1 t2 k) subst
- Nothing -> Nothing -- Fail
+1. The substitution we generate binds the *template type variables*
+ which are given to us explicitly.
-uTysX ty1 (AppTy s2 t2) k subst
- = case splitAppTy_maybe ty1 of
- Just (s1, t1) -> uTysX s1 s2 (uTysX t1 t2 k) subst
- Nothing -> Nothing -- Fail
+2. We want to match in the presence of foralls;
+ e.g (forall a. t1) ~ (forall b. t2)
- -- Not expecting for-alls in unification
-#ifdef DEBUG
-uTysX (ForAllTy _ _) ty2 k subst = panic "Unify.uTysX subst:ForAllTy (1st arg)"
-uTysX ty1 (ForAllTy _ _) k subst = panic "Unify.uTysX subst:ForAllTy (2nd arg)"
-#endif
+ That is what the RnEnv2 is for; it does the alpha-renaming
+ that makes it as if a and b were the same variable.
+ Initialising the RnEnv2, so that it can generate a fresh
+ binder when necessary, entails knowing the free variables of
+ both types.
- -- Anything else fails
-uTysX ty1 ty2 k subst = Nothing
+3. We must be careful not to bind a template type variable to a
+ locally bound variable. E.g.
+ (forall a. x) ~ (forall b. b)
+ where x is the template type variable. Then we do not want to
+ bind x to a/b! This is a kind of occurs check.
+ The necessary locals accumulate in the RnEnv2.
+
+
+\begin{code}
+data MatchEnv
+ = ME { me_tmpls :: VarSet -- Template tyvars
+ , me_env :: RnEnv2 -- Renaming envt for nested foralls
+ } -- In-scope set includes template tyvars
+
+tcMatchTys :: TyVarSet -- Template tyvars
+ -> [Type] -- Template
+ -> [Type] -- Target
+ -> Maybe TvSubst -- One-shot; in principle the template
+ -- variables could be free in the target
+
+tcMatchTys tmpls tys1 tys2
+ = case match_tys menv emptyTvSubstEnv tys1 tys2 of
+ Just subst_env -> Just (TvSubst in_scope subst_env)
+ Nothing -> Nothing
+ where
+ menv = ME { me_tmpls = tmpls, me_env = mkRnEnv2 in_scope }
+ in_scope = mkInScopeSet (tmpls `unionVarSet` tyVarsOfTypes tys2)
+ -- We're assuming that all the interesting
+ -- tyvars in tys1 are in tmpls
+
+-- This is similar, but extends a substitution
+tcMatchTyX :: TyVarSet -- Template tyvars
+ -> TvSubst -- Substitution to extend
+ -> Type -- Template
+ -> Type -- Target
+ -> Maybe TvSubst
+tcMatchTyX tmpls (TvSubst in_scope subst_env) ty1 ty2
+ = case match menv subst_env ty1 ty2 of
+ Just subst_env -> Just (TvSubst in_scope subst_env)
+ Nothing -> Nothing
+ where
+ menv = ME {me_tmpls = tmpls, me_env = mkRnEnv2 in_scope}
+
+tcMatchPreds
+ :: [TyVar] -- Bind these
+ -> [PredType] -> [PredType]
+ -> Maybe TvSubstEnv
+tcMatchPreds tmpls ps1 ps2
+ = match_list (match_pred menv) emptyTvSubstEnv ps1 ps2
+ where
+ menv = ME { me_tmpls = mkVarSet tmpls, me_env = mkRnEnv2 in_scope_tyvars }
+ in_scope_tyvars = mkInScopeSet (tyVarsOfTheta ps1 `unionVarSet` tyVarsOfTheta ps2)
+-- This one is called from the expression matcher, which already has a MatchEnv in hand
+ruleMatchTyX :: MatchEnv
+ -> TvSubstEnv -- Substitution to extend
+ -> Type -- Template
+ -> Type -- Target
+ -> Maybe TvSubstEnv
-uTyListsX [] [] k subst = k subst
-uTyListsX (ty1:tys1) (ty2:tys2) k subst = uTysX ty1 ty2 (uTyListsX tys1 tys2 k) subst
-uTyListsX tys1 tys2 k subst = Nothing -- Fail if the lists are different lengths
+ruleMatchTyX menv subst ty1 ty2 = match menv subst ty1 ty2 -- Rename for export
\end{code}
+Now the internals of matching
+
\begin{code}
--- Invariant: tv1 is a unifiable variable
-uVarX tv1 ty2 k subst@(tmpls, env)
- = case lookupVarEnv env tv1 of
- Just ty1 -> -- Already bound
- uTysX ty1 ty2 k subst
-
- Nothing -- Not already bound
- | typeKind ty2 `hasMoreBoxityInfo` tyVarKind tv1
- && occur_check_ok ty2
- -> -- No kind mismatch nor occur check
- k (tmpls, extendVarEnv env tv1 ty2)
-
- | otherwise -> Nothing -- Fail if kind mis-match or occur check
+match :: MatchEnv -- For the most part this is pushed downwards
+ -> TvSubstEnv -- Substitution so far:
+ -- Domain is subset of template tyvars
+ -- Free vars of range is subset of
+ -- in-scope set of the RnEnv2
+ -> Type -> Type -- Template and target respectively
+ -> Maybe TvSubstEnv
+-- This matcher works on source types; that is,
+-- it respects NewTypes and PredType
+
+match menv subst ty1 ty2 | Just ty1' <- tcView ty1 = match menv subst ty1' ty2
+match menv subst ty1 ty2 | Just ty2' <- tcView ty2 = match menv subst ty1 ty2'
+
+match menv subst (TyVarTy tv1) ty2
+ | tv1 `elemVarSet` me_tmpls menv
+ = case lookupVarEnv subst tv1' of
+ Nothing | any (inRnEnvR rn_env) (varSetElems (tyVarsOfType ty2))
+ -> Nothing -- Occurs check
+ | not (typeKind ty2 `isSubKind` tyVarKind tv1)
+ -> Nothing -- Kind mis-match
+ | otherwise
+ -> Just (extendVarEnv subst tv1 ty2)
+
+ Just ty1' | tcEqTypeX (nukeRnEnvL rn_env) ty1' ty2
+ -- ty1 has no locally-bound variables, hence nukeRnEnvL
+ -- Note tcEqType...we are doing source-type matching here
+ -> Just subst
+
+ other -> Nothing
+
+ | otherwise -- tv1 is not a template tyvar
+ = case ty2 of
+ TyVarTy tv2 | tv1' == rnOccR rn_env tv2 -> Just subst
+ other -> Nothing
where
- occur_check_ok ty = all occur_check_ok_tv (varSetElems (tyVarsOfType ty))
- occur_check_ok_tv tv | tv1 == tv = False
- | otherwise = case lookupVarEnv env tv of
- Nothing -> True
- Just ty -> occur_check_ok ty
+ rn_env = me_env menv
+ tv1' = rnOccL rn_env tv1
+
+match menv subst (ForAllTy tv1 ty1) (ForAllTy tv2 ty2)
+ = match menv' subst ty1 ty2
+ where -- Use the magic of rnBndr2 to go under the binders
+ menv' = menv { me_env = rnBndr2 (me_env menv) tv1 tv2 }
+
+match menv subst (PredTy p1) (PredTy p2)
+ = match_pred menv subst p1 p2
+match menv subst (TyConApp tc1 tys1) (TyConApp tc2 tys2)
+ | tc1 == tc2 = match_tys menv subst tys1 tys2
+match menv subst (FunTy ty1a ty1b) (FunTy ty2a ty2b)
+ = do { subst' <- match menv subst ty1a ty2a
+ ; match menv subst' ty1b ty2b }
+match menv subst (AppTy ty1a ty1b) ty2
+ | Just (ty2a, ty2b) <- repSplitAppTy_maybe ty2
+ = do { subst' <- match menv subst ty1a ty2a
+ ; match menv subst' ty1b ty2b }
+
+match menv subst ty1 ty2
+ = Nothing
+
+--------------
+match_tys menv subst tys1 tys2 = match_list (match menv) subst tys1 tys2
+
+--------------
+match_list :: (TvSubstEnv -> a -> a -> Maybe TvSubstEnv)
+ -> TvSubstEnv -> [a] -> [a] -> Maybe TvSubstEnv
+match_list fn subst [] [] = Just subst
+match_list fn subst (ty1:tys1) (ty2:tys2) = do { subst' <- fn subst ty1 ty2
+ ; match_list fn subst' tys1 tys2 }
+match_list fn subst tys1 tys2 = Nothing
+
+--------------
+match_pred menv subst (ClassP c1 tys1) (ClassP c2 tys2)
+ | c1 == c2 = match_tys menv subst tys1 tys2
+match_pred menv subst (IParam n1 t1) (IParam n2 t2)
+ | n1 == n2 = match menv subst t1 t2
+match_pred menv subst p1 p2 = Nothing
\end{code}
-
%************************************************************************
%* *
-\subsection{Matching on types}
+ Unification
%* *
%************************************************************************
-Matching is a {\em unidirectional} process, matching a type against a
-template (which is just a type with type variables in it). The
-matcher assumes that there are no repeated type variables in the
-template, so that it simply returns a mapping of type variables to
-types. It also fails on nested foralls.
+\begin{code}
+tcUnifyTys :: (TyVar -> BindFlag)
+ -> [Type] -> [Type]
+ -> Maybe TvSubst -- A regular one-shot substitution
+-- The two types may have common type variables, and indeed do so in the
+-- second call to tcUnifyTys in FunDeps.checkClsFD
+tcUnifyTys bind_fn tys1 tys2
+ = maybeErrToMaybe $ initUM bind_fn $
+ do { subst_env <- unify_tys emptyTvSubstEnv tys1 tys2
+
+ -- Find the fixed point of the resulting non-idempotent substitution
+ ; let in_scope = mkInScopeSet (tvs1 `unionVarSet` tvs2)
+ subst = TvSubst in_scope subst_env_fixpt
+ subst_env_fixpt = mapVarEnv (substTy subst) subst_env
+ ; return subst }
+ where
+ tvs1 = tyVarsOfTypes tys1
+ tvs2 = tyVarsOfTypes tys2
+
+----------------------------
+coreRefineTys :: DataCon -> [TyVar] -- Case pattern (con tv1 .. tvn ...)
+ -> Type -- Type of scrutinee
+ -> Maybe TypeRefinement
+
+type TypeRefinement = (TvSubstEnv, Bool)
+ -- The Bool is True iff all the bindings in the
+ -- env are for the pattern type variables
+ -- In this case, there is no type refinement
+ -- for already-in-scope type variables
+
+-- Used by Core Lint and the simplifier.
+coreRefineTys con tvs scrut_ty
+ = maybeErrToMaybe $ initUM (tryToBind tv_set) $
+ do { -- Run the unifier, starting with an empty env
+ ; subst_env <- unify emptyTvSubstEnv pat_res_ty scrut_ty
+
+ -- Find the fixed point of the resulting non-idempotent substitution
+ ; let subst = mkOpenTvSubst subst_env_fixpt
+ subst_env_fixpt = mapVarEnv (substTy subst) subst_env
+
+ ; return (subst_env_fixpt, all_bound_here subst_env) }
+ where
+ pat_res_ty = dataConInstResTy con (mkTyVarTys tvs)
+
+ -- 'tvs' are the tyvars bound by the pattern
+ tv_set = mkVarSet tvs
+ all_bound_here env = all bound_here (varEnvKeys env)
+ bound_here uniq = elemVarSetByKey uniq tv_set
+
+-- This version is used by the type checker
+gadtRefineTys :: TvSubst
+ -> DataCon -> [TyVar]
+ -> [Type] -> [Type]
+ -> MaybeErr Message (TvSubst, Bool)
+-- The bool is True <=> the only *new* bindings are for pat_tvs
+
+gadtRefineTys (TvSubst in_scope env1) con pat_tvs pat_tys ctxt_tys
+ = initUM (tryToBind tv_set) $
+ do { -- Run the unifier, starting with an empty env
+ ; env2 <- unify_tys env1 pat_tys ctxt_tys
+
+ -- Find the fixed point of the resulting non-idempotent substitution
+ ; let subst2 = TvSubst in_scope subst_env_fixpt
+ subst_env_fixpt = mapVarEnv (substTy subst2) env2
+
+ ; return (subst2, all_bound_here env2) }
+ where
+ -- 'tvs' are the tyvars bound by the pattern
+ tv_set = mkVarSet pat_tvs
+ all_bound_here env = all bound_here (varEnvKeys env)
+ bound_here uniq = elemVarEnvByKey uniq env1 || elemVarSetByKey uniq tv_set
+ -- The bool is True <=> the only *new* bindings are for pat_tvs
+
+----------------------------
+tryToBind :: TyVarSet -> TyVar -> BindFlag
+tryToBind tv_set tv | tv `elemVarSet` tv_set = BindMe
+ | otherwise = AvoidMe
+\end{code}
+
-@matchTys@ matches corresponding elements of a list of templates and
-types.
+%************************************************************************
+%* *
+ The workhorse
+%* *
+%************************************************************************
\begin{code}
-matchTy :: [GenTyVar flexi_tmpl] -- Template tyvars
- -> GenType flexi_tmpl -- Template
- -> GenType flexi_result -- Proposed instance of template
- -> Maybe (TyVarEnv (GenType flexi_result)) -- Matching substitution
-
-
-matchTys :: [GenTyVar flexi_tmpl] -- Template tyvars
- -> [GenType flexi_tmpl] -- Templates
- -> [GenType flexi_result] -- Proposed instance of template
- -> Maybe (TyVarEnv (GenType flexi_result), -- Matching substitution
- [GenType flexi_result]) -- Left over instance types
-
-matchTy tmpls ty1 ty2 = match ty1 ty2 (\(_,env) -> Just env)
- (tmpls, emptyVarEnv)
-
-matchTys tmpls tys1 tys2 = match_list tys1 tys2 (\((_,env),tys) -> Just (env,tys))
- (tmpls, emptyVarEnv)
+unify :: TvSubstEnv -- An existing substitution to extend
+ -> Type -> Type -- Types to be unified
+ -> UM TvSubstEnv -- Just the extended substitution,
+ -- Nothing if unification failed
+-- We do not require the incoming substitution to be idempotent,
+-- nor guarantee that the outgoing one is. That's fixed up by
+-- the wrappers.
+
+-- Respects newtypes, PredTypes
+
+unify subst ty1 ty2 = -- pprTrace "unify" (ppr subst <+> pprParendType ty1 <+> pprParendType ty2) $
+ unify_ subst ty1 ty2
+
+-- in unify_, any NewTcApps/Preds should be taken at face value
+unify_ subst (TyVarTy tv1) ty2 = uVar False subst tv1 ty2
+unify_ subst ty1 (TyVarTy tv2) = uVar True subst tv2 ty1
+
+unify_ subst ty1 ty2 | Just ty1' <- tcView ty1 = unify subst ty1' ty2
+unify_ subst ty1 ty2 | Just ty2' <- tcView ty2 = unify subst ty1 ty2'
+
+unify_ subst (PredTy p1) (PredTy p2) = unify_pred subst p1 p2
+
+unify_ subst t1@(TyConApp tyc1 tys1) t2@(TyConApp tyc2 tys2)
+ | tyc1 == tyc2 = unify_tys subst tys1 tys2
+
+unify_ subst (FunTy ty1a ty1b) (FunTy ty2a ty2b)
+ = do { subst' <- unify subst ty1a ty2a
+ ; unify subst' ty1b ty2b }
+
+ -- Applications need a bit of care!
+ -- They can match FunTy and TyConApp, so use splitAppTy_maybe
+ -- NB: we've already dealt with type variables and Notes,
+ -- so if one type is an App the other one jolly well better be too
+unify_ subst (AppTy ty1a ty1b) ty2
+ | Just (ty2a, ty2b) <- repSplitAppTy_maybe ty2
+ = do { subst' <- unify subst ty1a ty2a
+ ; unify subst' ty1b ty2b }
+
+unify_ subst ty1 (AppTy ty2a ty2b)
+ | Just (ty1a, ty1b) <- repSplitAppTy_maybe ty1
+ = do { subst' <- unify subst ty1a ty2a
+ ; unify subst' ty1b ty2b }
+
+unify_ subst ty1 ty2 = failWith (misMatch ty1 ty2)
+
+------------------------------
+unify_pred subst (ClassP c1 tys1) (ClassP c2 tys2)
+ | c1 == c2 = unify_tys subst tys1 tys2
+unify_pred subst (IParam n1 t1) (IParam n2 t2)
+ | n1 == n2 = unify subst t1 t2
+unify_pred subst p1 p2 = failWith (misMatch (PredTy p1) (PredTy p2))
+
+------------------------------
+unify_tys = unifyList unify
+
+unifyList :: Outputable a
+ => (TvSubstEnv -> a -> a -> UM TvSubstEnv)
+ -> TvSubstEnv -> [a] -> [a] -> UM TvSubstEnv
+unifyList unifier subst orig_xs orig_ys
+ = go subst orig_xs orig_ys
+ where
+ go subst [] [] = return subst
+ go subst (x:xs) (y:ys) = do { subst' <- unifier subst x y
+ ; go subst' xs ys }
+ go subst _ _ = failWith (lengthMisMatch orig_xs orig_ys)
+
+------------------------------
+uVar :: Bool -- Swapped
+ -> TvSubstEnv -- An existing substitution to extend
+ -> TyVar -- Type variable to be unified
+ -> Type -- with this type
+ -> UM TvSubstEnv
+
+uVar swap subst tv1 ty
+ = -- Check to see whether tv1 is refined by the substitution
+ case (lookupVarEnv subst tv1) of
+ -- Yes, call back into unify'
+ Just ty' | swap -> unify subst ty ty'
+ | otherwise -> unify subst ty' ty
+ -- No, continue
+ Nothing -> uUnrefined subst tv1 ty ty
+
+
+uUnrefined :: TvSubstEnv -- An existing substitution to extend
+ -> TyVar -- Type variable to be unified
+ -> Type -- with this type
+ -> Type -- (de-noted version)
+ -> UM TvSubstEnv
+
+-- We know that tv1 isn't refined
+
+uUnrefined subst tv1 ty2 ty2'
+ | Just ty2'' <- tcView ty2'
+ = uUnrefined subst tv1 ty2 ty2'' -- Unwrap synonyms
+ -- This is essential, in case we have
+ -- type Foo a = a
+ -- and then unify a :=: Foo a
+
+uUnrefined subst tv1 ty2 (TyVarTy tv2)
+ | tv1 == tv2 -- Same type variable
+ = return subst
+
+ -- Check to see whether tv2 is refined
+ | Just ty' <- lookupVarEnv subst tv2
+ = uUnrefined subst tv1 ty' ty'
+
+ -- So both are unrefined; next, see if the kinds force the direction
+ | k1 == k2 -- Can update either; so check the bind-flags
+ = do { b1 <- tvBindFlag tv1
+ ; b2 <- tvBindFlag tv2
+ ; case (b1,b2) of
+ (BindMe, _) -> bind tv1 ty2
+
+ (AvoidMe, BindMe) -> bind tv2 ty1
+ (AvoidMe, _) -> bind tv1 ty2
+
+ (WildCard, WildCard) -> return subst
+ (WildCard, Skolem) -> return subst
+ (WildCard, _) -> bind tv2 ty1
+
+ (Skolem, WildCard) -> return subst
+ (Skolem, Skolem) -> failWith (misMatch ty1 ty2)
+ (Skolem, _) -> bind tv2 ty1
+ }
+
+ | k1 `isSubKind` k2 = bindTv subst tv2 ty1 -- Must update tv2
+ | k2 `isSubKind` k1 = bindTv subst tv1 ty2 -- Must update tv1
+
+ | otherwise = failWith (kindMisMatch tv1 ty2)
+ where
+ ty1 = TyVarTy tv1
+ k1 = tyVarKind tv1
+ k2 = tyVarKind tv2
+ bind tv ty = return (extendVarEnv subst tv ty)
+
+uUnrefined subst tv1 ty2 ty2' -- ty2 is not a type variable
+ | tv1 `elemVarSet` substTvSet subst (tyVarsOfType ty2')
+ = failWith (occursCheck tv1 ty2) -- Occurs check
+ | not (k2 `isSubKind` k1)
+ = failWith (kindMisMatch tv1 ty2) -- Kind check
+ | otherwise
+ = bindTv subst tv1 ty2 -- Bind tyvar to the synonym if poss
+ where
+ k1 = tyVarKind tv1
+ k2 = typeKind ty2'
+
+substTvSet :: TvSubstEnv -> TyVarSet -> TyVarSet
+-- Apply the non-idempotent substitution to a set of type variables,
+-- remembering that the substitution isn't necessarily idempotent
+substTvSet subst tvs
+ = foldVarSet (unionVarSet . get) emptyVarSet tvs
+ where
+ get tv = case lookupVarEnv subst tv of
+ Nothing -> unitVarSet tv
+ Just ty -> substTvSet subst (tyVarsOfType ty)
+
+bindTv subst tv ty -- ty is not a type variable
+ = do { b <- tvBindFlag tv
+ ; case b of
+ Skolem -> failWith (misMatch (TyVarTy tv) ty)
+ WildCard -> return subst
+ other -> return (extendVarEnv subst tv ty)
+ }
\end{code}
-@match@ is the main function.
+%************************************************************************
+%* *
+ Unification monad
+%* *
+%************************************************************************
\begin{code}
-match :: GenType flexi_tmpl -> GenType flexi_result -- Current match pair
- -> (Subst flexi_tmpl flexi_result -> Maybe result) -- Continuation
- -> Subst flexi_tmpl flexi_result -- Current substitution
- -> Maybe result
-
--- When matching against a type variable, see if the variable
--- has already been bound. If so, check that what it's bound to
--- is the same as ty; if not, bind it and carry on.
-
-match (TyVarTy v) ty k = \ s@(tmpls,env) ->
- if v `elem` tmpls then
- -- v is a template variable
- case lookupVarEnv env v of
- Nothing -> k (tmpls, extendVarEnv env v ty)
- Just ty' | ty' == ty -> k s -- Succeeds
- | otherwise -> Nothing -- Fails
- else
- -- v is not a template variable; ty had better match
- -- Can't use (==) because types differ
- case ty of
- TyVarTy v' | getUnique v == getUnique v'
- -> k s -- Success
- other -> Nothing -- Failure
-
-match (FunTy arg1 res1) (FunTy arg2 res2) k = match arg1 arg2 (match res1 res2 k)
-match (AppTy fun1 arg1) ty2 k = case splitAppTy_maybe ty2 of
- Just (fun2,arg2) -> match fun1 fun2 (match arg1 arg2 k)
- Nothing -> \ _ -> Nothing -- Fail
-match (TyConApp tc1 tys1) (TyConApp tc2 tys2) k | tc1 == tc2
- = match_list tys1 tys2 ( \(s,tys2') ->
- if null tys2' then
- k s -- Succeed
- else
- Nothing -- Fail
- )
-
- -- With type synonyms, we have to be careful for the exact
- -- same reasons as in the unifier. Please see the
- -- considerable commentary there before changing anything
- -- here! (WDP 95/05)
-match (NoteTy _ ty1) ty2 k = match ty1 ty2 k
-match ty1 (NoteTy _ ty2) k = match ty1 ty2 k
-
--- Catch-all fails
-match _ _ _ = \s -> Nothing
-
-match_list [] tys2 k = \s -> k (s, tys2)
-match_list (ty1:tys1) [] k = \s -> Nothing -- Not enough arg tys => failure
-match_list (ty1:tys1) (ty2:tys2) k = match ty1 ty2 (match_list tys1 tys2 k)
+data BindFlag
+ = BindMe -- A regular type variable
+ | AvoidMe -- Like BindMe but, given the choice, avoid binding it
+
+ | Skolem -- This type variable is a skolem constant
+ -- Don't bind it; it only matches itself
+
+ | WildCard -- This type variable matches anything,
+ -- and does not affect the substitution
+
+newtype UM a = UM { unUM :: (TyVar -> BindFlag)
+ -> MaybeErr Message a }
+
+instance Monad UM where
+ return a = UM (\tvs -> Succeeded a)
+ fail s = UM (\tvs -> Failed (text s))
+ m >>= k = UM (\tvs -> case unUM m tvs of
+ Failed err -> Failed err
+ Succeeded v -> unUM (k v) tvs)
+
+initUM :: (TyVar -> BindFlag) -> UM a -> MaybeErr Message a
+initUM badtvs um = unUM um badtvs
+
+tvBindFlag :: TyVar -> UM BindFlag
+tvBindFlag tv = UM (\tv_fn -> Succeeded (tv_fn tv))
+
+failWith :: Message -> UM a
+failWith msg = UM (\tv_fn -> Failed msg)
+
+maybeErrToMaybe :: MaybeErr fail succ -> Maybe succ
+maybeErrToMaybe (Succeeded a) = Just a
+maybeErrToMaybe (Failed m) = Nothing
+
+------------------------------
+repSplitAppTy_maybe :: Type -> Maybe (Type,Type)
+-- Like Type.splitAppTy_maybe, but any coreView 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) = case snocView tys of
+ Just (tys', ty') -> Just (TyConApp tc tys', ty')
+ Nothing -> Nothing
+repSplitAppTy_maybe other = Nothing
\end{code}
+
+%************************************************************************
+%* *
+ Error reporting
+ We go to a lot more trouble to tidy the types
+ in TcUnify. Maybe we'll end up having to do that
+ here too, but I'll leave it for now.
+%* *
+%************************************************************************
+
+\begin{code}
+misMatch t1 t2
+ = ptext SLIT("Can't match types") <+> quotes (ppr t1) <+>
+ ptext SLIT("and") <+> quotes (ppr t2)
+
+lengthMisMatch tys1 tys2
+ = sep [ptext SLIT("Can't match unequal length lists"),
+ nest 2 (ppr tys1), nest 2 (ppr tys2) ]
+
+kindMisMatch tv1 t2
+ = vcat [ptext SLIT("Can't match kinds") <+> quotes (ppr (tyVarKind tv1)) <+>
+ ptext SLIT("and") <+> quotes (ppr (typeKind t2)),
+ ptext SLIT("when matching") <+> quotes (ppr tv1) <+>
+ ptext SLIT("with") <+> quotes (ppr t2)]
+
+occursCheck tv ty
+ = hang (ptext SLIT("Can't construct the infinite type"))
+ 2 (ppr tv <+> equals <+> ppr ty)
+\end{code}
\ No newline at end of file
projects / ghc-hetmet.git / blobdiff