3 -- Matching and unification
4 tcMatchTys, tcMatchTyX, ruleMatchTyX, tcMatchPreds, MatchEnv(..),
8 gadtRefineTys, BindFlag(..),
10 coreRefineTys, TypeRefinement,
16 #include "HsVersions.h"
18 import Var ( Var, TyVar, tyVarKind )
21 import Kind ( isSubKind )
22 import Type ( typeKind, tyVarsOfType, tyVarsOfTypes, tyVarsOfTheta, mkTyVarTys,
23 TvSubstEnv, emptyTvSubstEnv, TvSubst(..), substTy, tcEqTypeX )
24 import TypeRep ( Type(..), PredType(..), funTyCon )
25 import DataCon ( DataCon, dataConInstResTy )
26 import Util ( snocView )
27 import ErrUtils ( Message )
33 %************************************************************************
37 %************************************************************************
40 Matching is much tricker than you might think.
42 1. The substitution we generate binds the *template type variables*
43 which are given to us explicitly.
45 2. We want to match in the presence of foralls;
46 e.g (forall a. t1) ~ (forall b. t2)
48 That is what the RnEnv2 is for; it does the alpha-renaming
49 that makes it as if a and b were the same variable.
50 Initialising the RnEnv2, so that it can generate a fresh
51 binder when necessary, entails knowing the free variables of
54 3. We must be careful not to bind a template type variable to a
55 locally bound variable. E.g.
56 (forall a. x) ~ (forall b. b)
57 where x is the template type variable. Then we do not want to
58 bind x to a/b! This is a kind of occurs check.
59 The necessary locals accumulate in the RnEnv2.
64 = ME { me_tmpls :: VarSet -- Template tyvars
65 , me_env :: RnEnv2 -- Renaming envt for nested foralls
66 } -- In-scope set includes template tyvars
68 tcMatchTys :: TyVarSet -- Template tyvars
71 -> Maybe TvSubst -- One-shot; in principle the template
72 -- variables could be free in the target
74 tcMatchTys tmpls tys1 tys2
75 = case match_tys menv emptyTvSubstEnv tys1 tys2 of
76 Just subst_env -> Just (TvSubst in_scope subst_env)
79 menv = ME { me_tmpls = tmpls, me_env = mkRnEnv2 in_scope }
80 in_scope = mkInScopeSet (tmpls `unionVarSet` tyVarsOfTypes tys2)
81 -- We're assuming that all the interesting
82 -- tyvars in tys1 are in tmpls
84 -- This is similar, but extends a substitution
85 tcMatchTyX :: TyVarSet -- Template tyvars
86 -> TvSubst -- Substitution to extend
90 tcMatchTyX tmpls (TvSubst in_scope subst_env) ty1 ty2
91 = case match menv subst_env ty1 ty2 of
92 Just subst_env -> Just (TvSubst in_scope subst_env)
95 menv = ME {me_tmpls = tmpls, me_env = mkRnEnv2 in_scope}
98 :: [TyVar] -- Bind these
99 -> [PredType] -> [PredType]
101 tcMatchPreds tmpls ps1 ps2
102 = match_list (match_pred menv) emptyTvSubstEnv ps1 ps2
104 menv = ME { me_tmpls = mkVarSet tmpls, me_env = mkRnEnv2 in_scope_tyvars }
105 in_scope_tyvars = mkInScopeSet (tyVarsOfTheta ps1 `unionVarSet` tyVarsOfTheta ps2)
107 -- This one is called from the expression matcher, which already has a MatchEnv in hand
108 ruleMatchTyX :: MatchEnv
109 -> TvSubstEnv -- Substitution to extend
114 ruleMatchTyX menv subst ty1 ty2 = match menv subst ty1 ty2 -- Rename for export
117 Now the internals of matching
120 match :: MatchEnv -- For the most part this is pushed downwards
121 -> TvSubstEnv -- Substitution so far:
122 -- Domain is subset of template tyvars
123 -- Free vars of range is subset of
124 -- in-scope set of the RnEnv2
125 -> Type -> Type -- Template and target respectively
127 -- This matcher works on source types; that is,
128 -- it respects NewTypes and PredType
130 match menv subst (NoteTy _ ty1) ty2 = match menv subst ty1 ty2
131 match menv subst ty1 (NoteTy _ ty2) = match menv subst ty1 ty2
133 match menv subst (TyVarTy tv1) ty2
134 | tv1 `elemVarSet` me_tmpls menv
135 = case lookupVarEnv subst tv1' of
136 Nothing | any (inRnEnvR rn_env) (varSetElems (tyVarsOfType ty2))
137 -> Nothing -- Occurs check
138 | not (typeKind ty2 `isSubKind` tyVarKind tv1)
139 -> Nothing -- Kind mis-match
141 -> Just (extendVarEnv subst tv1 ty2)
143 Just ty1' | tcEqTypeX (nukeRnEnvL rn_env) ty1' ty2
144 -- ty1 has no locally-bound variables, hence nukeRnEnvL
145 -- Note tcEqType...we are doing source-type matching here
150 | otherwise -- tv1 is not a template tyvar
152 TyVarTy tv2 | tv1' == rnOccR rn_env tv2 -> Just subst
156 tv1' = rnOccL rn_env tv1
158 match menv subst (ForAllTy tv1 ty1) (ForAllTy tv2 ty2)
159 = match menv' subst ty1 ty2
160 where -- Use the magic of rnBndr2 to go under the binders
161 menv' = menv { me_env = rnBndr2 (me_env menv) tv1 tv2 }
163 match menv subst (PredTy p1) (PredTy p2)
164 = match_pred menv subst p1 p2
165 match menv subst (TyConApp tc1 tys1) (TyConApp tc2 tys2)
166 | tc1 == tc2 = match_tys menv subst tys1 tys2
167 match menv subst (FunTy ty1a ty1b) (FunTy ty2a ty2b)
168 = do { subst' <- match menv subst ty1a ty2a
169 ; match menv subst' ty1b ty2b }
170 match menv subst (AppTy ty1a ty1b) ty2
171 | Just (ty2a, ty2b) <- repSplitAppTy_maybe ty2
172 = do { subst' <- match menv subst ty1a ty2a
173 ; match menv subst' ty1b ty2b }
175 match menv subst ty1 ty2
179 match_tys menv subst tys1 tys2 = match_list (match menv) subst tys1 tys2
182 match_list :: (TvSubstEnv -> a -> a -> Maybe TvSubstEnv)
183 -> TvSubstEnv -> [a] -> [a] -> Maybe TvSubstEnv
184 match_list fn subst [] [] = Just subst
185 match_list fn subst (ty1:tys1) (ty2:tys2) = do { subst' <- fn subst ty1 ty2
186 ; match_list fn subst' tys1 tys2 }
187 match_list fn subst tys1 tys2 = Nothing
190 match_pred menv subst (ClassP c1 tys1) (ClassP c2 tys2)
191 | c1 == c2 = match_tys menv subst tys1 tys2
192 match_pred menv subst (IParam n1 t1) (IParam n2 t2)
193 | n1 == n2 = match menv subst t1 t2
194 match_pred menv subst p1 p2 = Nothing
198 %************************************************************************
202 %************************************************************************
205 tcUnifyTys :: (TyVar -> BindFlag)
207 -> Maybe TvSubst -- A regular one-shot substitution
208 -- The two types may have common type variables, and indeed do so in the
209 -- second call to tcUnifyTys in FunDeps.checkClsFD
210 tcUnifyTys bind_fn tys1 tys2
211 = maybeErrToMaybe $ initUM bind_fn $
212 do { subst_env <- unify_tys emptyTvSubstEnv tys1 tys2
214 -- Find the fixed point of the resulting non-idempotent substitution
215 ; let in_scope = mkInScopeSet (tvs1 `unionVarSet` tvs2)
216 subst = TvSubst in_scope subst_env_fixpt
217 subst_env_fixpt = mapVarEnv (substTy subst) subst_env
220 tvs1 = tyVarsOfTypes tys1
221 tvs2 = tyVarsOfTypes tys2
223 ----------------------------
224 coreRefineTys :: InScopeSet -- Superset of free vars of either type
225 -> DataCon -> [TyVar] -- Case pattern (con tv1 .. tvn ...)
226 -> Type -- Type of scrutinee
227 -> Maybe TypeRefinement
229 type TypeRefinement = (TvSubstEnv, Bool)
230 -- The Bool is True iff all the bindings in the
231 -- env are for the pattern type variables
232 -- In this case, there is no type refinement
233 -- for already-in-scope type variables
235 -- Used by Core Lint and the simplifier.
236 coreRefineTys in_scope con tvs scrut_ty
237 = maybeErrToMaybe $ initUM (tryToBind tv_set) $
238 do { -- Run the unifier, starting with an empty env
239 ; subst_env <- unify emptyTvSubstEnv pat_res_ty scrut_ty
241 -- Find the fixed point of the resulting non-idempotent substitution
242 ; let subst = TvSubst in_scope subst_env_fixpt
243 subst_env_fixpt = mapVarEnv (substTy subst) subst_env
245 ; return (subst_env_fixpt, all_bound_here subst_env) }
247 pat_res_ty = dataConInstResTy con (mkTyVarTys tvs)
249 -- 'tvs' are the tyvars bound by the pattern
250 tv_set = mkVarSet tvs
251 all_bound_here env = all bound_here (varEnvKeys env)
252 bound_here uniq = elemVarSetByKey uniq tv_set
255 ----------------------------
257 :: (TyVar -> BindFlag) -- Try to unify these
258 -> TvSubstEnv -- Not idempotent
260 -> MaybeErr Message TvSubstEnv -- Not idempotent
261 -- This one is used by the type checker. Neither the input nor result
262 -- substitition is idempotent
263 gadtRefineTys bind_fn subst tys1 tys2
264 = initUM bind_fn (unify_tys subst tys1 tys2)
266 ----------------------------
267 tryToBind :: TyVarSet -> TyVar -> BindFlag
268 tryToBind tv_set tv | tv `elemVarSet` tv_set = BindMe
269 | otherwise = AvoidMe
273 %************************************************************************
277 %************************************************************************
280 unify :: TvSubstEnv -- An existing substitution to extend
281 -> Type -> Type -- Types to be unified
282 -> UM TvSubstEnv -- Just the extended substitution,
283 -- Nothing if unification failed
284 -- We do not require the incoming substitution to be idempotent,
285 -- nor guarantee that the outgoing one is. That's fixed up by
288 -- Respects newtypes, PredTypes
290 unify subst ty1 ty2 = -- pprTrace "unify" (ppr subst <+> pprParendType ty1 <+> pprParendType ty2) $
293 -- in unify_, any NewTcApps/Preds should be taken at face value
294 unify_ subst (TyVarTy tv1) ty2 = uVar False subst tv1 ty2
295 unify_ subst ty1 (TyVarTy tv2) = uVar True subst tv2 ty1
297 unify_ subst (NoteTy _ ty1) ty2 = unify subst ty1 ty2
298 unify_ subst ty1 (NoteTy _ ty2) = unify subst ty1 ty2
300 unify_ subst (PredTy p1) (PredTy p2) = unify_pred subst p1 p2
302 unify_ subst t1@(TyConApp tyc1 tys1) t2@(TyConApp tyc2 tys2)
303 | tyc1 == tyc2 = unify_tys subst tys1 tys2
305 unify_ subst (FunTy ty1a ty1b) (FunTy ty2a ty2b)
306 = do { subst' <- unify subst ty1a ty2a
307 ; unify subst' ty1b ty2b }
309 -- Applications need a bit of care!
310 -- They can match FunTy and TyConApp, so use splitAppTy_maybe
311 -- NB: we've already dealt with type variables and Notes,
312 -- so if one type is an App the other one jolly well better be too
313 unify_ subst (AppTy ty1a ty1b) ty2
314 | Just (ty2a, ty2b) <- repSplitAppTy_maybe ty2
315 = do { subst' <- unify subst ty1a ty2a
316 ; unify subst' ty1b ty2b }
318 unify_ subst ty1 (AppTy ty2a ty2b)
319 | Just (ty1a, ty1b) <- repSplitAppTy_maybe ty1
320 = do { subst' <- unify subst ty1a ty2a
321 ; unify subst' ty1b ty2b }
323 unify_ subst ty1 ty2 = failWith (misMatch ty1 ty2)
325 ------------------------------
326 unify_pred subst (ClassP c1 tys1) (ClassP c2 tys2)
327 | c1 == c2 = unify_tys subst tys1 tys2
328 unify_pred subst (IParam n1 t1) (IParam n2 t2)
329 | n1 == n2 = unify subst t1 t2
330 unify_pred subst p1 p2 = failWith (misMatch (PredTy p1) (PredTy p2))
332 ------------------------------
333 unify_tys = unifyList unify
335 unifyList :: Outputable a
336 => (TvSubstEnv -> a -> a -> UM TvSubstEnv)
337 -> TvSubstEnv -> [a] -> [a] -> UM TvSubstEnv
338 unifyList unifier subst orig_xs orig_ys
339 = go subst orig_xs orig_ys
341 go subst [] [] = return subst
342 go subst (x:xs) (y:ys) = do { subst' <- unifier subst x y
344 go subst _ _ = failWith (lengthMisMatch orig_xs orig_ys)
346 ------------------------------
347 uVar :: Bool -- Swapped
348 -> TvSubstEnv -- An existing substitution to extend
349 -> TyVar -- Type variable to be unified
350 -> Type -- with this type
353 uVar swap subst tv1 ty
354 = -- Check to see whether tv1 is refined by the substitution
355 case (lookupVarEnv subst tv1) of
356 -- Yes, call back into unify'
357 Just ty' | swap -> unify subst ty ty'
358 | otherwise -> unify subst ty' ty
360 Nothing -> uUnrefined subst tv1 ty ty
363 uUnrefined :: TvSubstEnv -- An existing substitution to extend
364 -> TyVar -- Type variable to be unified
365 -> Type -- with this type
366 -> Type -- (de-noted version)
369 -- We know that tv1 isn't refined
371 uUnrefined subst tv1 ty2 (NoteTy _ ty2')
372 = uUnrefined subst tv1 ty2 ty2' -- Unwrap synonyms
373 -- This is essential, in case we have
375 -- and then unify a :=: Foo a
377 uUnrefined subst tv1 ty2 (TyVarTy tv2)
378 | tv1 == tv2 -- Same type variable
381 -- Check to see whether tv2 is refined
382 | Just ty' <- lookupVarEnv subst tv2
383 = uUnrefined subst tv1 ty' ty'
385 -- So both are unrefined; next, see if the kinds force the direction
386 | k1 == k2 -- Can update either; so check the bind-flags
387 = do { b1 <- tvBindFlag tv1
388 ; b2 <- tvBindFlag tv2
390 (BindMe, _) -> bind tv1 ty2
392 (AvoidMe, BindMe) -> bind tv2 ty1
393 (AvoidMe, _) -> bind tv1 ty2
395 (WildCard, WildCard) -> return subst
396 (WildCard, Skolem) -> return subst
397 (WildCard, _) -> bind tv2 ty1
399 (Skolem, WildCard) -> return subst
400 (Skolem, Skolem) -> failWith (misMatch ty1 ty2)
401 (Skolem, _) -> bind tv2 ty1
404 | k1 `isSubKind` k2 = bindTv subst tv2 ty1 -- Must update tv2
405 | k2 `isSubKind` k1 = bindTv subst tv1 ty2 -- Must update tv1
407 | otherwise = failWith (kindMisMatch tv1 ty2)
412 bind tv ty = return (extendVarEnv subst tv ty)
414 uUnrefined subst tv1 ty2 ty2' -- ty2 is not a type variable
415 | tv1 `elemVarSet` substTvSet subst (tyVarsOfType ty2')
416 = failWith (occursCheck tv1 ty2) -- Occurs check
417 | not (k2 `isSubKind` k1)
418 = failWith (kindMisMatch tv1 ty2) -- Kind check
420 = bindTv subst tv1 ty2 -- Bind tyvar to the synonym if poss
425 substTvSet :: TvSubstEnv -> TyVarSet -> TyVarSet
426 -- Apply the non-idempotent substitution to a set of type variables,
427 -- remembering that the substitution isn't necessarily idempotent
429 = foldVarSet (unionVarSet . get) emptyVarSet tvs
431 get tv = case lookupVarEnv subst tv of
432 Nothing -> unitVarSet tv
433 Just ty -> substTvSet subst (tyVarsOfType ty)
435 bindTv subst tv ty -- ty is not a type variable
436 = do { b <- tvBindFlag tv
438 Skolem -> failWith (misMatch (TyVarTy tv) ty)
439 WildCard -> return subst
440 other -> return (extendVarEnv subst tv ty)
444 %************************************************************************
448 %************************************************************************
452 = BindMe -- A regular type variable
453 | AvoidMe -- Like BindMe but, given the choice, avoid binding it
455 | Skolem -- This type variable is a skolem constant
456 -- Don't bind it; it only matches itself
458 | WildCard -- This type variable matches anything,
459 -- and does not affect the substitution
461 newtype UM a = UM { unUM :: (TyVar -> BindFlag)
462 -> MaybeErr Message a }
464 instance Monad UM where
465 return a = UM (\tvs -> Succeeded a)
466 fail s = UM (\tvs -> Failed (text s))
467 m >>= k = UM (\tvs -> case unUM m tvs of
468 Failed err -> Failed err
469 Succeeded v -> unUM (k v) tvs)
471 initUM :: (TyVar -> BindFlag) -> UM a -> MaybeErr Message a
472 initUM badtvs um = unUM um badtvs
474 tvBindFlag :: TyVar -> UM BindFlag
475 tvBindFlag tv = UM (\tv_fn -> Succeeded (tv_fn tv))
477 failWith :: Message -> UM a
478 failWith msg = UM (\tv_fn -> Failed msg)
480 maybeErrToMaybe :: MaybeErr fail succ -> Maybe succ
481 maybeErrToMaybe (Succeeded a) = Just a
482 maybeErrToMaybe (Failed m) = Nothing
484 ------------------------------
485 repSplitAppTy_maybe :: Type -> Maybe (Type,Type)
486 -- Like Type.splitAppTy_maybe, but any coreView stuff is already done
487 repSplitAppTy_maybe (FunTy ty1 ty2) = Just (TyConApp funTyCon [ty1], ty2)
488 repSplitAppTy_maybe (AppTy ty1 ty2) = Just (ty1, ty2)
489 repSplitAppTy_maybe (TyConApp tc tys) = case snocView tys of
490 Just (tys', ty') -> Just (TyConApp tc tys', ty')
492 repSplitAppTy_maybe other = Nothing
496 %************************************************************************
499 We go to a lot more trouble to tidy the types
500 in TcUnify. Maybe we'll end up having to do that
501 here too, but I'll leave it for now.
503 %************************************************************************
507 = ptext SLIT("Can't match types") <+> quotes (ppr t1) <+>
508 ptext SLIT("and") <+> quotes (ppr t2)
510 lengthMisMatch tys1 tys2
511 = sep [ptext SLIT("Can't match unequal length lists"),
512 nest 2 (ppr tys1), nest 2 (ppr tys2) ]
515 = vcat [ptext SLIT("Can't match kinds") <+> quotes (ppr (tyVarKind tv1)) <+>
516 ptext SLIT("and") <+> quotes (ppr (typeKind t2)),
517 ptext SLIT("when matching") <+> quotes (ppr tv1) <+>
518 ptext SLIT("with") <+> quotes (ppr t2)]
521 = hang (ptext SLIT("Can't construct the infinite type"))
522 2 (ppr tv <+> equals <+> ppr ty)