TcInteract.lhs 98.5 KB
 simonpj@microsoft.com committed Sep 13, 2010 1 2 3 \begin{code} module TcInteract ( solveInteract, AtomicInert,  4  InertSet, emptyInert, updInertSet, extractUnsolved, solveOne  simonpj@microsoft.com committed Sep 13, 2010 5 6 7 8  ) where #include "HsVersions.h"  dimitris@microsoft.com committed Oct 04, 2010 9   simonpj@microsoft.com committed Sep 13, 2010 10 11 12 13 import BasicTypes import TcCanonical import VarSet import Type  dimitris@microsoft.com committed Oct 04, 2010 14 import TypeRep  simonpj@microsoft.com committed Sep 13, 2010 15 16  import Id  simonpj@microsoft.com committed Oct 07, 2010 17 import VarEnv  simonpj@microsoft.com committed Sep 13, 2010 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 import Var import TcType import HsBinds import InstEnv import Class import TyCon import Name import FunDeps import Control.Monad ( when ) import Coercion import Outputable import TcRnTypes import TcErrors import TcSMonad  simonpj@microsoft.com committed Oct 07, 2010 38 import Bag  dimitris@microsoft.com committed Oct 04, 2010 39 40 41 import qualified Data.Map as Map import Maybes  simonpj@microsoft.com committed Sep 13, 2010 42 43 44 45 46 import Control.Monad( zipWithM, unless ) import FastString ( sLit ) import DynFlags \end{code}  dimitris@microsoft.com committed Oct 06, 2010 47 Note [InertSet invariants]  simonpj@microsoft.com committed Sep 13, 2010 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 ~~~~~~~~~~~~~~~~~~~~~~~~~~~ An InertSet is a bag of canonical constraints, with the following invariants: 1 No two constraints react with each other. A tricky case is when there exists a given (solved) dictionary constraint and a wanted identical constraint in the inert set, but do not react because reaction would create loopy dictionary evidence for the wanted. See note [Recursive dictionaries] 2 Given equalities form an idempotent substitution [none of the given LHS's occur in any of the given RHS's or reactant parts] 3 Wanted equalities also form an idempotent substitution 4 The entire set of equalities is acyclic. 5 Wanted dictionaries are inert with the top-level axiom set 6 Equalities of the form tv1 ~ tv2 always have a touchable variable on the left (if possible). 7 No wanted constraints tv1 ~ tv2 with tv1 touchable. Such constraints will be marked as solved right before being pushed into the inert set. See note [Touchables and givens]. Note that 6 and 7 are /not/ enforced by canonicalization but rather by insertion in the inert list, ie by TcInteract. During the process of solving, the inert set will contain some previously given constraints, some wanted constraints, and some given constraints which have arisen from solving wanted constraints. For now we do not distinguish between given and solved constraints. Note that we must switch wanted inert items to given when going under an implication constraint (when in top-level inference mode).  dimitris@microsoft.com committed Oct 06, 2010 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 Note [InertSet FlattenSkolemEqClass] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The inert_fsks field of the inert set contains an "inverse map" of all the flatten skolem equalities in the inert set. For instance, if inert_cts looks like this: fsk1 ~ fsk2 fsk3 ~ fsk2 fsk4 ~ fsk5 Then, the inert_fsks fields holds the following map: fsk2 |-> { fsk1, fsk3 } fsk5 |-> { fsk4 } Along with the necessary coercions to convert fsk1 and fsk3 back to fsk2 and fsk4 back to fsk5. Hence, the invariants of the inert_fsks field are: (a) All TcTyVars in the domain and range of inert_fsks are flatten skolems (b) All TcTyVars in the domain of inert_fsk occur naked as rhs in some equalities of inert_cts (c) For every mapping fsk1 |-> { (fsk2,co), ... } it must be: co : fsk2 ~ fsk1 The role of the inert_fsks is to make it easy to maintain the equivalence class of each flatten skolem, which is much needed to correctly do spontaneous solving. See Note [Loopy Spontaneous Solving]  simonpj@microsoft.com committed Sep 13, 2010 109 110 \begin{code}  111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 data CCanMap a = CCanMap { cts_givder :: Map.Map a CanonicalCts -- Invariant: all Given or Derived , cts_wanted :: Map.Map a CanonicalCts } -- Invariant: all Wanted cCanMapToBag :: Ord a => CCanMap a -> CanonicalCts cCanMapToBag cmap = Map.fold unionBags rest_cts (cts_givder cmap) where rest_cts = Map.fold unionBags emptyCCan (cts_wanted cmap) emptyCCanMap :: CCanMap a emptyCCanMap = CCanMap { cts_givder = Map.empty, cts_wanted = Map.empty } updCCanMap:: Ord a => (a,CanonicalCt) -> CCanMap a -> CCanMap a updCCanMap (a,ct) cmap = case cc_flavor ct of Wanted {} -> cmap { cts_wanted = Map.insertWith unionBags a this_ct (cts_wanted cmap) } _ -> cmap { cts_givder = Map.insertWith unionBags a this_ct (cts_givder cmap) } where this_ct = singleCCan ct getRelevantCts :: Ord a => a -> CCanMap a -> (CanonicalCts, CCanMap a) -- Gets the relevant constraints and returns the rest of the CCanMap getRelevantCts a cmap = let relevant = unionBags (Map.findWithDefault emptyCCan a (cts_wanted cmap)) (Map.findWithDefault emptyCCan a (cts_givder cmap)) residual_map = cmap { cts_wanted = Map.delete a (cts_wanted cmap) , cts_givder = Map.delete a (cts_givder cmap) } in (relevant, residual_map) extractUnsolvedCMap :: Ord a => CCanMap a -> (CanonicalCts, CCanMap a) -- Gets the wanted constraints and returns a residual CCanMap extractUnsolvedCMap cmap = let unsolved = Map.fold unionBags emptyCCan (cts_wanted cmap) in (unsolved, cmap { cts_wanted = Map.empty})  simonpj@microsoft.com committed Sep 13, 2010 146 -- See Note [InertSet invariants]  dimitris@microsoft.com committed Oct 04, 2010 147 data InertSet  148 149 150 151 152 153 154 155 156  = IS { inert_eqs :: CanonicalCts -- Equalities only (CTyEqCan) , inert_dicts :: CCanMap Class -- Dictionaries only , inert_ips :: CCanMap (IPName Name) -- Implicit parameters , inert_funeqs :: CCanMap TyCon -- Type family equalities only -- This representation allows us to quickly get to the relevant -- inert constraints when interacting a work item with the inert set.  157 158  , inert_fds :: FDImprovements -- List of pairwise improvements that have kicked in already -- and reside either in the worklist or in the inerts  dimitris@microsoft.com committed Oct 04, 2010 159  , inert_fsks :: Map.Map TcTyVar [(TcTyVar,Coercion)] }  dimitris@microsoft.com committed Oct 06, 2010 160  -- See Note [InertSet FlattenSkolemEqClass]  dimitris@microsoft.com committed Oct 04, 2010 161   162 163 164 type FDImprovement = (PredType,PredType) type FDImprovements = [(PredType,PredType)]  simonpj@microsoft.com committed Sep 13, 2010 165 instance Outputable InertSet where  166  ppr is = vcat [ vcat (map ppr (Bag.bagToList $inert_eqs is))  167 168 169  , vcat (map ppr (Bag.bagToList$ cCanMapToBag (inert_dicts is))) , vcat (map ppr (Bag.bagToList $cCanMapToBag (inert_ips is))) , vcat (map ppr (Bag.bagToList$ cCanMapToBag (inert_funeqs is)))  dimitris@microsoft.com committed Oct 04, 2010 170 171 172 173 174  , vcat (map (\(v,rest) -> ppr v <+> text "|->" <+> hsep (map (ppr.fst) rest)) (Map.toList $inert_fsks is) ) ]  simonpj@microsoft.com committed Sep 13, 2010 175 emptyInert :: InertSet  176 177 178 179 180 emptyInert = IS { inert_eqs = Bag.emptyBag , inert_dicts = emptyCCanMap , inert_ips = emptyCCanMap , inert_funeqs = emptyCCanMap , inert_fsks = Map.empty, inert_fds = [] }  dimitris@microsoft.com committed Oct 04, 2010 181 182 183  updInertSet :: InertSet -> AtomicInert -> InertSet -- Introduces an element in the inert set for the first time  184 updInertSet is@(IS { inert_eqs = eqs, inert_fsks = fsks })  dimitris@microsoft.com committed Oct 04, 2010 185 186 187 188 189 190  item@(CTyEqCan { cc_id = cv , cc_tyvar = tv1 , cc_rhs = xi }) | Just tv2 <- tcGetTyVar_maybe xi, FlatSkol {} <- tcTyVarDetails tv1, FlatSkol {} <- tcTyVarDetails tv2  191  = let eqs' = eqs Bag.snocBag item  dimitris@microsoft.com committed Oct 04, 2010 192  fsks' = Map.insertWith (++) tv2 [(tv1, mkCoVarCoercion cv)] fsks  dimitris@microsoft.com committed Oct 06, 2010 193  -- See Note [InertSet FlattenSkolemEqClass]  194 195 196 197 198 199 200 201 202 203 204  in is { inert_eqs = eqs', inert_fsks = fsks' } updInertSet is item | isCTyEqCan item -- Other equality = let eqs' = inert_eqs is Bag.snocBag item in is { inert_eqs = eqs' } | Just cls <- isCDictCan_Maybe item -- Dictionary = is { inert_dicts = updCCanMap (cls,item) (inert_dicts is) } | Just x <- isCIPCan_Maybe item -- IP = is { inert_ips = updCCanMap (x,item) (inert_ips is) } | Just tc <- isCFunEqCan_Maybe item -- Function equality = is { inert_funeqs = updCCanMap (tc,item) (inert_funeqs is) }  205  | otherwise  206  = pprPanic "Unknown form of constraint!" (ppr item)  207 208 209 210  updInertSetFDImprs :: InertSet -> Maybe FDImprovement -> InertSet updInertSetFDImprs is (Just fdi) = is { inert_fds = fdi : inert_fds is } updInertSetFDImprs is Nothing = is  dimitris@microsoft.com committed Oct 04, 2010 211   212 213 214 215 216 foldISEqCtsM :: Monad m => (a -> AtomicInert -> m a) -> a -> InertSet -> m a -- Fold over the equalities of the inerts foldISEqCtsM k z IS { inert_eqs = eqs } = Bag.foldlBagM k z eqs  simonpj@microsoft.com committed Sep 13, 2010 217 extractUnsolved :: InertSet -> (InertSet, CanonicalCts)  218 219 220 221 222 extractUnsolved is@(IS {inert_eqs = eqs}) = let is_init = is { inert_eqs = emptyCCan , inert_dicts = solved_dicts , inert_ips = solved_ips , inert_funeqs = solved_funeqs }  223  is_final = Bag.foldlBag updInertSet is_init solved_eqs -- Add equalities carefully  224 225 226 227 228 229  in (is_final, unsolved) where (unsolved_eqs, solved_eqs) = Bag.partitionBag isWantedCt eqs (unsolved_ips, solved_ips) = extractUnsolvedCMap (inert_ips is) (unsolved_dicts, solved_dicts) = extractUnsolvedCMap (inert_dicts is) (unsolved_funeqs, solved_funeqs) = extractUnsolvedCMap (inert_funeqs is)  simonpj@microsoft.com committed Sep 13, 2010 230   231 232  unsolved = unsolved_eqs unionBags unsolved_ips unionBags unsolved_dicts unionBags unsolved_funeqs  dimitris@microsoft.com committed Oct 04, 2010 233 234  getFskEqClass :: InertSet -> TcTyVar -> [(TcTyVar,Coercion)]  dimitris@microsoft.com committed Oct 06, 2010 235 -- Precondition: tv is a FlatSkol. See Note [InertSet FlattenSkolemEqClass]  236 getFskEqClass (IS { inert_eqs = cts, inert_fsks = fsks }) tv  dimitris@microsoft.com committed Oct 04, 2010 237 238 239 240 241 242 243 244 245 246 247 248 249 250  = case lkpTyEqCanByLhs of Nothing -> fromMaybe [] (Map.lookup tv fsks) Just ceq -> case tcGetTyVar_maybe (cc_rhs ceq) of Just tv_rhs | FlatSkol {} <- tcTyVarDetails tv_rhs -> let ceq_co = mkSymCoercion$ mkCoVarCoercion (cc_id ceq) mk_co (v,c) = (v, mkTransCoercion c ceq_co) in (tv_rhs, ceq_co): map mk_co (fromMaybe [] $Map.lookup tv fsks) _ -> [] where lkpTyEqCanByLhs = Bag.foldlBag lkp Nothing cts lkp :: Maybe CanonicalCt -> CanonicalCt -> Maybe CanonicalCt lkp Nothing ct@(CTyEqCan {cc_tyvar = tv'}) | tv' == tv = Just ct lkp other _ct = other  251 252 253 254 haveBeenImproved :: FDImprovements -> PredType -> PredType -> Bool haveBeenImproved [] _ _ = False haveBeenImproved ((pty1,pty2):fdimprs) pty1' pty2' | tcEqPred pty1 pty1' && tcEqPred pty2 pty2'  255  = True  256  | tcEqPred pty1 pty2' && tcEqPred pty2 pty1'  257 258 259  = True | otherwise = haveBeenImproved fdimprs pty1' pty2'  260   261 getFDImprovements :: InertSet -> FDImprovements  262 -- Return a list of the improvements that have kicked in so far  263 getFDImprovements = inert_fds  dimitris@microsoft.com committed Oct 04, 2010 264   simonpj@microsoft.com committed Sep 13, 2010 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 \end{code} Note [Touchables and givens] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Touchable variables will never show up in givens which are inputs to the solver. However, touchables may show up in givens generated by the flattener. For example, axioms: G Int ~ Char F Char ~ Int wanted: F (G alpha) ~w Int canonicalises to G alpha ~g b F b ~w Int which can be put in the inert set. Suppose we also have a wanted alpha ~w Int We cannot rewrite the given G alpha ~g b using the wanted alpha ~w Int. Instead, after reacting alpha ~w Int with the whole inert set, we observe that we can solve it by unifying alpha with Int, so we mark it as solved and put it back in the *work list*. [We also immediately unify alpha := Int, without telling anyone, see trySpontaneousSolve function, to avoid doing this in the end.] Later, because it is solved (given, in effect), we can use it to rewrite G alpha ~g b to G Int ~g b, which gets put back in the work list. Eventually, we will dispatch the remaining wanted constraints using the top-level axioms. Finally, note that after reacting a wanted equality with the entire inert set we may end up with something like b ~w alpha which we should flip around to generate the solved constraint alpha ~s b. %********************************************************************* %* * * Main Interaction Solver * * * ********************************************************************** Note [Basic plan] ~~~~~~~~~~~~~~~~~ 1. Canonicalise (unary) 2. Pairwise interaction (binary) * Take one from work list * Try all pair-wise interactions with each constraint in inert  319 320 321 322  As an optimisation, we prioritize the equalities both in the worklist and in the inerts.  simonpj@microsoft.com committed Sep 13, 2010 323 324 325 326 327 328 329 330 3. Try to solve spontaneously for equalities involving touchables 4. Top-level interaction (binary wrt top-level) Superclass decomposition belongs in (4), see note [Superclasses] \begin{code} type AtomicInert = CanonicalCt -- constraint pulled from InertSet type WorkItem = CanonicalCt -- constraint pulled from WorkList  331 332 -- A mixture of Given, Wanted, and Derived constraints. -- We split between equalities and the rest to process equalities first.  simonpj@microsoft.com committed Oct 20, 2010 333 334 type WorkList = CanonicalCts type SWorkList = WorkList -- A worklist of solved  simonpj@microsoft.com committed Sep 13, 2010 335 336  unionWorkLists :: WorkList -> WorkList -> WorkList  simonpj@microsoft.com committed Oct 20, 2010 337 unionWorkLists = andCCan  simonpj@microsoft.com committed Sep 13, 2010 338 339  isEmptyWorkList :: WorkList -> Bool  simonpj@microsoft.com committed Oct 20, 2010 340 isEmptyWorkList = isEmptyCCan  simonpj@microsoft.com committed Sep 13, 2010 341 342  emptyWorkList :: WorkList  simonpj@microsoft.com committed Oct 20, 2010 343 emptyWorkList = emptyCCan  344   345 workListFromCCan :: CanonicalCt -> WorkList  simonpj@microsoft.com committed Oct 20, 2010 346 workListFromCCan = singleCCan  dimitris@microsoft.com committed Oct 04, 2010 347   simonpj@microsoft.com committed Oct 20, 2010 348 ------------------------  simonpj@microsoft.com committed Sep 13, 2010 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 data StopOrContinue = Stop -- Work item is consumed | ContinueWith WorkItem -- Not consumed instance Outputable StopOrContinue where ppr Stop = ptext (sLit "Stop") ppr (ContinueWith w) = ptext (sLit "ContinueWith") <+> ppr w -- Results after interacting a WorkItem as far as possible with an InertSet data StageResult = SR { sr_inerts :: InertSet -- The new InertSet to use (REPLACES the old InertSet) , sr_new_work :: WorkList -- Any new work items generated (should be ADDED to the old WorkList) -- Invariant: -- sr_stop = Just workitem => workitem is *not* in sr_inerts and -- workitem is inert wrt to sr_inerts , sr_stop :: StopOrContinue } instance Outputable StageResult where ppr (SR { sr_inerts = inerts, sr_new_work = work, sr_stop = stop }) = ptext (sLit "SR") <+> braces (sep [ ptext (sLit "inerts =") <+> ppr inerts <> comma , ptext (sLit "new work =") <+> ppr work <> comma , ptext (sLit "stop =") <+> ppr stop]) type SimplifierStage = WorkItem -> InertSet -> TcS StageResult -- Combine a sequence of simplifier 'stages' to create a pipeline runSolverPipeline :: [(String, SimplifierStage)] -> InertSet -> WorkItem -> TcS (InertSet, WorkList) -- Precondition: non-empty list of stages runSolverPipeline pipeline inerts workItem = do { traceTcS "Start solver pipeline"$ vcat [ ptext (sLit "work item =") <+> ppr workItem , ptext (sLit "inerts =") <+> ppr inerts] ; let itr_in = SR { sr_inerts = inerts , sr_new_work = emptyWorkList , sr_stop = ContinueWith workItem } ; itr_out <- run_pipeline pipeline itr_in ; let new_inert = case sr_stop itr_out of Stop -> sr_inerts itr_out  dimitris@microsoft.com committed Oct 04, 2010 395  ContinueWith item -> sr_inerts itr_out updInertSet item  simonpj@microsoft.com committed Sep 13, 2010 396 397 398 399 400 401 402 403 404 405 406 407 408  ; return (new_inert, sr_new_work itr_out) } where run_pipeline :: [(String, SimplifierStage)] -> StageResult -> TcS StageResult run_pipeline [] itr = return itr run_pipeline _ itr@(SR { sr_stop = Stop }) = return itr run_pipeline ((name,stage):stages) (SR { sr_new_work = accum_work , sr_inerts = inerts , sr_stop = ContinueWith work_item }) = do { itr <- stage work_item inerts ; traceTcS ("Stage result (" ++ name ++ ")") (ppr itr)  409  ; let itr' = itr { sr_new_work = accum_work unionWorkLists sr_new_work itr }  simonpj@microsoft.com committed Sep 13, 2010 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440  ; run_pipeline stages itr' } \end{code} Example 1: Inert: {c ~ d, F a ~ t, b ~ Int, a ~ ty} (all given) Reagent: a ~ [b] (given) React with (c~d) ==> IR (ContinueWith (a~[b])) True [] React with (F a ~ t) ==> IR (ContinueWith (a~[b])) False [F [b] ~ t] React with (b ~ Int) ==> IR (ContinueWith (a~[Int]) True [] Example 2: Inert: {c ~w d, F a ~g t, b ~w Int, a ~w ty} Reagent: a ~w [b] React with (c ~w d) ==> IR (ContinueWith (a~[b])) True [] React with (F a ~g t) ==> IR (ContinueWith (a~[b])) True [] (can't rewrite given with wanted!) etc. Example 3: Inert: {a ~ Int, F Int ~ b} (given) Reagent: F a ~ b (wanted) React with (a ~ Int) ==> IR (ContinueWith (F Int ~ b)) True [] React with (F Int ~ b) ==> IR Stop True [] -- after substituting we re-canonicalize and get nothing \begin{code} -- Main interaction solver: we fully solve the worklist 'in one go', -- returning an extended inert set. -- -- See Note [Touchables and givens].  441 solveInteract :: InertSet -> CanonicalCts -> TcS InertSet  simonpj@microsoft.com committed Sep 13, 2010 442 443 solveInteract inert ws = do { dyn_flags <- getDynFlags  simonpj@microsoft.com committed Oct 20, 2010 444  ; solveInteractWithDepth (ctxtStkDepth dyn_flags,0,[]) inert ws  simonpj@microsoft.com committed Sep 13, 2010 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463  } solveOne :: InertSet -> WorkItem -> TcS InertSet solveOne inerts workItem = do { dyn_flags <- getDynFlags ; solveOneWithDepth (ctxtStkDepth dyn_flags,0,[]) inerts workItem } ----------------- solveInteractWithDepth :: (Int, Int, [WorkItem]) -> InertSet -> WorkList -> TcS InertSet solveInteractWithDepth ctxt@(max_depth,n,stack) inert ws | isEmptyWorkList ws = return inert | n > max_depth = solverDepthErrorTcS n stack | otherwise = do { traceTcS "solveInteractWithDepth" $ simonpj@microsoft.com committed Oct 20, 2010 464 465 466 467  vcat [ text "Current depth =" <+> ppr n , text "Max depth =" <+> ppr max_depth ] -- Solve equalities first  468  ; let (eqs, non_eqs) = Bag.partitionBag isCTyEqCan ws  simonpj@microsoft.com committed Oct 20, 2010 469 470  ; is_from_eqs <- Bag.foldlBagM (solveOneWithDepth ctxt) inert eqs ; Bag.foldlBagM (solveOneWithDepth ctxt) is_from_eqs non_eqs }  simonpj@microsoft.com committed Sep 13, 2010 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493  ------------------ -- Fully interact the given work item with an inert set, and return a -- new inert set which has assimilated the new information. solveOneWithDepth :: (Int, Int, [WorkItem]) -> InertSet -> WorkItem -> TcS InertSet solveOneWithDepth (max_depth, n, stack) inert work = do { traceTcS0 (indent ++ "Solving {") (ppr work) ; (new_inert, new_work) <- runSolverPipeline thePipeline inert work ; traceTcS0 (indent ++ "Subgoals:") (ppr new_work) -- Recursively solve the new work generated -- from workItem, with a greater depth ; res_inert <- solveInteractWithDepth (max_depth, n+1, work:stack) new_inert new_work ; traceTcS0 (indent ++ "Done }") (ppr work) ; return res_inert } where indent = replicate (2*n) ' ' thePipeline :: [(String,SimplifierStage)]  494 495 496 497 thePipeline = [ ("interact with inert eqs", interactWithInertEqsStage) , ("interact with inerts", interactWithInertsStage) , ("spontaneous solve", spontaneousSolveStage) , ("top-level reactions", topReactionsStage) ]  simonpj@microsoft.com committed Sep 13, 2010 498 499 500 501 502 503 504 505 \end{code} ********************************************************************************* * * The spontaneous-solve Stage * * *********************************************************************************  506 507 508 509 510 511 Note [Efficient Orientation] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ There are two cases where we have to be careful about orienting equalities to get better efficiency.  512 Case 2: In Rewriting Equalities (function rewriteEqLHS)  513   514 515 516 517 518 519 520 521 522 523  When rewriting two equalities with the same LHS: (a) (tv ~ xi1) (b) (tv ~ xi2) We have a choice of producing work (xi1 ~ xi2) (up-to the canonicalization invariants) However, to prevent the inert items from getting kicked out of the inerts first, we prefer to canonicalize (xi1 ~ xi2) if (b) comes from the inert set, or (xi2 ~ xi1) if (a) comes from the inert set. This choice is implemented using the WhichComesFromInert flag.  524   525 526 Case 2: In Spontaneous Solving Example 2a:  527 528 529 530 531 532 533 534 535 536 537 538 539  Inerts: [w1] : D alpha [w2] : C beta [w3] : F alpha ~ Int [w4] : H beta ~ Int Untouchables = [beta] Then a wanted (beta ~ alpha) comes along. 1) While interacting with the inerts it is going to kick w2,w4 out of the inerts 2) Then, it will spontaneoulsy be solved by (alpha := beta) 3) Now (and here is the tricky part), to add him back as solved (alpha ~ beta) is no good because, in the next iteration, it will kick out w1,w3 as well so we will end up with *all* the inert equalities back in the worklist!  540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559  So it is tempting to just add (beta ~ alpha) instead, that is, maintain the original orietnation of the constraint. But that does not work very well, because it may cause the "double unification problem" (See Note [Avoid double unifications]). For instance: Example 2b: [w1] : fsk1 ~ alpha [w2] : fsk2 ~ alpha --- At the end of the interaction suppose we spontaneously solve alpha := fsk1 but keep [Given] fsk1 ~ alpha. Then, the second time around we see the constraint (fsk2 ~ alpha), and we unify *again* alpha := fsk2, which is wrong. Our conclusion is that, while in some cases (Example 2a), it makes sense to preserve the original orientation, it is hard to do this in a sound way. So we *don't* do this for now, @solveWithIdentity@ outputs a constraint that is oriented with the unified variable on the left.  560 561 562 563  Case 3: Functional Dependencies and IP improvement work TODO. Optimisation not yet implemented there.  simonpj@microsoft.com committed Sep 13, 2010 564 565 566 \begin{code} spontaneousSolveStage :: SimplifierStage spontaneousSolveStage workItem inerts  567  = do { mSolve <- trySpontaneousSolve workItem inerts  simonpj@microsoft.com committed Sep 13, 2010 568 569  ; case mSolve of Nothing -> -- no spontaneous solution for him, keep going  570 571  return$ SR { sr_new_work = emptyWorkList , sr_inerts = inerts  simonpj@microsoft.com committed Sep 13, 2010 572 573  , sr_stop = ContinueWith workItem }  574  Just (workItem', workList')  simonpj@microsoft.com committed Oct 20, 2010 575 576 577 578 579 580 581 582 583 584 585  | not (isGivenCt workItem) -- Original was wanted or derived but we have now made him -- given so we have to interact him with the inerts due to -- its status change. This in turn may produce more work. -- We do this *right now* (rather than just putting workItem' -- back into the work-list) because we've solved -> do { (new_inert, new_work) <- runSolverPipeline [ ("recursive interact with inert eqs", interactWithInertEqsStage) , ("recursive interact with inerts", interactWithInertsStage) ] inerts workItem' ; return $SR { sr_new_work = new_work unionWorkLists workList'  586 587  , sr_inerts = new_inert -- will include workItem' , sr_stop = Stop }  simonpj@microsoft.com committed Oct 20, 2010 588  }  589 590 591 592 593 594  | otherwise -> -- Original was given; he must then be inert all right, and -- workList' are all givens from flattening return$ SR { sr_new_work = workList' , sr_inerts = inerts updInertSet workItem' , sr_stop = Stop }  dimitris@microsoft.com committed Oct 04, 2010 595  }  dimitris@microsoft.com committed Oct 06, 2010 596   simonpj@microsoft.com committed Sep 13, 2010 597 598 599 600 601 -- @trySpontaneousSolve wi@ solves equalities where one side is a -- touchable unification variable. Returns: -- * Nothing if we were not able to solve it -- * Just wi' if we solved it, wi' (now a "given") should be put in the work list. -- See Note [Touchables and givens]  602 -- NB: just passing the inerts through for the skolem equivalence classes  603 trySpontaneousSolve :: WorkItem -> InertSet -> TcS (Maybe (WorkItem, SWorkList))  604 trySpontaneousSolve workItem@(CTyEqCan { cc_id = cv, cc_flavor = gw, cc_tyvar = tv1, cc_rhs = xi }) inerts  simonpj@microsoft.com committed Oct 07, 2010 605 606  | isGiven gw = return Nothing  simonpj@microsoft.com committed Sep 13, 2010 607 608 609 610  | Just tv2 <- tcGetTyVar_maybe xi = do { tch1 <- isTouchableMetaTyVar tv1 ; tch2 <- isTouchableMetaTyVar tv2 ; case (tch1, tch2) of  dimitris@microsoft.com committed Oct 04, 2010 611  (True, True) -> trySpontaneousEqTwoWay inerts cv gw tv1 tv2  612 613  (True, False) -> trySpontaneousEqOneWay inerts cv gw tv1 xi (False, True) -> trySpontaneousEqOneWay inerts cv gw tv2 (mkTyVarTy tv1)  simonpj@microsoft.com committed Sep 13, 2010 614 615 616  _ -> return Nothing } | otherwise = do { tch1 <- isTouchableMetaTyVar tv1  617  ; if tch1 then trySpontaneousEqOneWay inerts cv gw tv1 xi  618 619 620  else do { traceTcS "Untouchable LHS, can't spontaneously solve workitem:" (ppr workItem) ; return Nothing } }  simonpj@microsoft.com committed Sep 13, 2010 621 622 623 624  -- No need for -- trySpontaneousSolve (CFunEqCan ...) = ... -- See Note [No touchables as FunEq RHS] in TcSMonad  dimitris@microsoft.com committed Oct 04, 2010 625 trySpontaneousSolve _ _ = return Nothing  simonpj@microsoft.com committed Sep 13, 2010 626 627  ----------------  628 629 630 631 trySpontaneousEqOneWay :: InertSet -> CoVar -> CtFlavor -> TcTyVar -> Xi -> TcS (Maybe (WorkItem,SWorkList)) -- tv is a MetaTyVar, not untouchable trySpontaneousEqOneWay inerts cv gw tv xi  632  | not (isSigTyVar tv) || isTyVarTy xi  633 634 635 636  = do { kxi <- zonkTcTypeTcS xi >>= return . typeKind -- Must look through the TcTyBinds -- hence kxi and not typeKind xi -- See Note [Kind Errors] ; if kxi isSubKind tyVarKind tv then  637  solveWithIdentity inerts cv gw tv xi  638  else if tyVarKind tv isSubKind kxi then  639 640 641 642 643  return Nothing -- kinds are compatible but we can't solveWithIdentity this way -- This case covers the a_touchable :: * ~ b_untouchable :: ?? -- which has to be deferred or floated out for someone else to solve -- it in a scope where 'b' is no longer untouchable. else kindErrorTcS gw (mkTyVarTy tv) xi -- See Note [Kind errors]  644  }  645 646  | otherwise -- Still can't solve, sig tyvar and non-variable rhs = return Nothing  simonpj@microsoft.com committed Sep 13, 2010 647 648  ----------------  dimitris@microsoft.com committed Oct 04, 2010 649 trySpontaneousEqTwoWay :: InertSet -> CoVar -> CtFlavor -> TcTyVar -> TcTyVar  650  -> TcS (Maybe (WorkItem,SWorkList))  651 -- Both tyvars are *touchable* MetaTyvars so there is only a chance for kind error here  dimitris@microsoft.com committed Oct 04, 2010 652 trySpontaneousEqTwoWay inerts cv gw tv1 tv2  653  | k1 isSubKind k2  654  , nicer_to_update_tv2 = solveWithIdentity inerts cv gw tv2 (mkTyVarTy tv1)  655  | k2 isSubKind k1  656  = solveWithIdentity inerts cv gw tv1 (mkTyVarTy tv2)  657 658  | otherwise -- None is a subkind of the other, but they are both touchable! = kindErrorTcS gw (mkTyVarTy tv1) (mkTyVarTy tv2) -- See Note [Kind errors]  simonpj@microsoft.com committed Sep 13, 2010 659 660 661 662 663 664  where k1 = tyVarKind tv1 k2 = tyVarKind tv2 nicer_to_update_tv2 = isSigTyVar tv1 || isSystemName (Var.varName tv2) \end{code}  665 666 667 668 669 670 671 672 673 674 675 Note [Kind errors] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider the wanted problem: alpha ~ (# Int, Int #) where alpha :: ?? and (# Int, Int #) :: (#). We can't spontaneously solve this constraint, but we should rather reject the program that give rise to it. If 'trySpontaneousEqTwoWay' simply returns @Nothing@ then that wanted constraint is going to propagate all the way and get quantified over in inference mode. That's bad because we do know at this point that the constraint is insoluble. Instead, we call 'kindErrorTcS' here, which immediately fails. The same applies in canonicalization code in case of kind errors in the givens.  676   677 678 679 680 681 682 683 684 685 686 687 However, when we canonicalize givens we only check for compatibility (@compatKind@). If there were a kind error in the givens, this means some form of inconsistency or dead code. When we spontaneously solve wanteds we may have to look through the bindings, hence we call zonkTcTypeTcS above. The reason is that maybe xi is @alpha@ where alpha :: ? and a previous spontaneous solving has set (alpha := f) with (f :: *). The reason that xi is still alpha and not f is becasue the solved constraint may be oriented as (f ~ alpha) instead of (alpha ~ f). Then we should be using @xi@s "real" kind, which is * and not ?, when we try to detect whether spontaneous solving is possible.  688 689 690 691 692 693 694 695 696 697 Note [Spontaneous solving and kind compatibility] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Note that our canonical constraints insist that only *given* equalities (tv ~ xi) or (F xis ~ rhs) require the LHS and the RHS to have exactly the same kinds. - We have to require this because: Given equalities can be freely used to rewrite inside other types or constraints. - We do not have to do the same for wanteds because:  698 699 700 701 702 703 704 705  First, wanted equations (tv ~ xi) where tv is a touchable unification variable may have kinds that do not agree (the kind of xi must be a sub kind of the kind of tv). Second, any potential kind mismatch will result in the constraint not being soluble, which will be reported anyway. This is the reason that @trySpontaneousOneWay@ and @trySpontaneousTwoWay@ will perform a kind compatibility check, and only then will they proceed to @solveWithIdentity@.  706 707 708 709 710 711 712 713 714 715 716  Caveat: - Givens from higher-rank, such as: type family T b :: * -> * -> * type instance T Bool = (->) f :: forall a. ((T a ~ (->)) => ...) -> a -> ... flop = f (...) True Whereas we would be able to apply the type instance, we would not be able to use the given (T Bool ~ (->)) in the body of 'flop'  717 Note [Loopy Spontaneous Solving]  simonpj@microsoft.com committed Sep 13, 2010 718 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  719   720 721 Example 1: [The problem of loopy spontaneous solving] ----------  simonpj@microsoft.com committed Sep 13, 2010 722 723 724 725 726 727 728 729 730 731 732 Consider the original wanted: wanted : Maybe (E alpha) ~ alpha where E is a type family, such that E (T x) = x. After canonicalization, as a result of flattening, we will get: given : E alpha ~ fsk wanted : alpha ~ Maybe fsk where (fsk := E alpha, on the side). Now, if we spontaneously *solve* (alpha := Maybe fsk) we are in trouble! Instead, we should refrain from solving it and keep it as wanted. In inference mode we'll end up quantifying over (alpha ~ Maybe (E alpha)) Hence, 'solveWithIdentity' performs a small occurs check before  dimitris@microsoft.com committed Oct 06, 2010 733 734 735 736 737 actually solving. But this occurs check *must look through* flatten skolems. However, it may be the case that the flatten skolem in hand is equal to some other flatten skolem whith *does not* mention our unification variable. Here's a typical example:  738 739 Example 2: [The need of keeping track of flatten skolem equivalence classes] ----------  dimitris@microsoft.com committed Oct 06, 2010 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 Original wanteds: g: F alpha ~ F beta w: alpha ~ F alpha After canonicalization: g: F beta ~ f1 g: F alpha ~ f1 w: alpha ~ f2 g: F alpha ~ f2 After some reactions: g: f1 ~ f2 g: F beta ~ f1 w: alpha ~ f2 g: F alpha ~ f2 At this point, we will try to spontaneously solve (alpha ~ f2) which remains as yet unsolved. We will look inside f2, which immediately mentions (F alpha), so it's not good to unify! However by looking at the equivalence class of the flatten skolems, we can see that it is fine to unify (alpha ~ f1) which solves our goals!  758 759 Example 3: [The need of looking through TyBinds for already spontaneously solved variables] ----------  dimitris@microsoft.com committed Oct 06, 2010 760 761 762 763 764 765 766 767 768 769 770 771 772 A similar problem happens because of other spontaneous solving. Suppose we have the following wanteds, arriving in this exact order: (first) w: beta ~ alpha (second) w: alpha ~ fsk (third) g: F beta ~ fsk Then, we first spontaneously solve the first constraint, making (beta := alpha), and having (beta ~ alpha) as given. *Then* we encounter the second wanted (alpha ~ fsk). "fsk" does not obviously mention alpha, so naively we can also spontaneously solve (alpha := fsk). But that is wrong since fsk mentions beta, which has already secretly been unified to alpha! To avoid this problem, the same occurs check must unveil rewritings that can happen because of spontaneously having solved other constraints.  773 774 Example 4: [Orientation of (tv ~ xi) equalities] ----------  775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 We orient equalities (tv ~ xi) so that flatten skolems appear on the left, if possible. Here is an example of why this is needed: [Wanted] w1: alpha ~ fsk [Given] g1: F alpha ~ fsk [Given] g2: b ~ fsk Flatten skolem equivalence class = [] Assume that g2 is *not* oriented properly, as shown above. Then we would like to spontaneously solve w1 but we can't set alpha := fsk, since fsk hides the type F alpha. However, by using the equation g2 it would be possible to solve w1 by setting alpha := b. In other words, it is not enough to look at a flatten skolem equivalence class to try to find alternatives to unify with. We may have to go to other variables. By orienting the equalities so that flatten skolems are in the LHS we are eliminating them as much as possible from the RHS of other wanted equalities, and hence it suffices to look in their flatten skolem equivalence classes.  793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 NB: This situation appears in the IndTypesPerf test case, inside indexed-types/. Caveat: You may wonder if we should be doing this for unification variables as well. However, Note [Efficient Orientation], Case 2, demonstrates that this is not possible at least for touchable unification variables which we have to keep oriented with the touchable on the LHS to be able to eliminate it. So then, what about untouchables? Example 4a: ----------- Untouchable = beta, Touchable = alpha [Wanted] w1: alpha ~ fsk [Given] g1: F alpha ~ fsk [Given] g2: beta ~ fsk Flatten skolem equivalence class = [] Should we be able to unify alpha := beta to solve the constraint? Arguably yes, but that implies that an *untouchable* unification variable (beta) is in the same equivalence class as a flatten skolem that mentions @alpha@. I.e. g2 means that: beta ~ F alpha But I do not think that there is any way to produce evidence for such a constraint from the outside other than beta := F alpha, which violates the OutsideIn-ness.  simonpj@microsoft.com committed Sep 13, 2010 817 818 819 820 821 822 823  Note [Avoid double unifications] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The spontaneous solver has to return a given which mentions the unified unification variable *on the left* of the equality. Here is what happens if not: Original wanted: (a ~ alpha), (alpha ~ Int) We spontaneously solve the first wanted, without changing the order!  simonpj@microsoft.com committed Oct 07, 2010 824  given : a ~ alpha [having unified alpha := a]  simonpj@microsoft.com committed Sep 13, 2010 825 826 827 Now the second wanted comes along, but he cannot rewrite the given, so we simply continue. At the end we spontaneously solve that guy, *reunifying* [alpha := Int]  simonpj@microsoft.com committed Oct 07, 2010 828 829 830 We avoid this problem by orienting the given so that the unification variable is on the left. [Note that alternatively we could attempt to enforce this at canonicalization]  simonpj@microsoft.com committed Sep 13, 2010 831   simonpj@microsoft.com committed Oct 07, 2010 832 833 834 See also Note [No touchables as FunEq RHS] in TcSMonad; avoiding double unifications is the main reason we disallow touchable unification variables as RHS of type family equations: F xis ~ alpha.  simonpj@microsoft.com committed Sep 13, 2010 835 836 837  \begin{code} ----------------  838 solveWithIdentity :: InertSet  dimitris@microsoft.com committed Oct 04, 2010 839  -> CoVar -> CtFlavor -> TcTyVar -> Xi  840  -> TcS (Maybe (WorkItem, SWorkList))  simonpj@microsoft.com committed Sep 13, 2010 841 842 -- Solve with the identity coercion -- Precondition: kind(xi) is a sub-kind of kind(tv)  simonpj@microsoft.com committed Oct 07, 2010 843 844 845 -- Precondition: CtFlavor is Wanted or Derived -- See [New Wanted Superclass Work] to see why solveWithIdentity -- must work for Derived as well as Wanted  846 847 848 849 850 -- Returns: (workItem, workList) where -- workItem = the new Given constraint -- workList = some additional work that may have been produced as a result of flattening -- in case we did some chasing through flatten skolem equivalence classes. solveWithIdentity inerts cv gw tv xi  simonpj@microsoft.com committed Oct 07, 2010 851  = do { tybnds <- getTcSTyBindsMap  simonpj@microsoft.com committed Oct 07, 2010 852 853 854 855  ; case occurCheck tybnds inerts tv xi of Nothing -> return Nothing Just (xi_unflat,coi) -> solve_with xi_unflat coi } where  856  solve_with xi_unflat coi -- coi : xi_unflat ~ xi  simonpj@microsoft.com committed Oct 07, 2010 857  = do { traceTcS "Sneaky unification:" $ dimitris@microsoft.com committed Oct 04, 2010 858 859 860 861  vcat [text "Coercion variable: " <+> ppr gw, text "Coercion: " <+> pprEq (mkTyVarTy tv) xi, text "Left Kind is : " <+> ppr (typeKind (mkTyVarTy tv)), text "Right Kind is : " <+> ppr (typeKind xi)  simonpj@microsoft.com committed Oct 07, 2010 862  ]  863 864 865  ; setWantedTyBind tv xi_unflat -- Set tv := xi_unflat ; cv_given <- newGivOrDerCoVar (mkTyVarTy tv) xi_unflat xi_unflat  simonpj@microsoft.com committed Oct 07, 2010 866  ; let flav = mkGivenFlavor gw UnkSkol  867 868 869 870 871 872 873 874 875  ; (ct,cts, co) <- case coi of ACo co -> do { (cc,ccs) <- canEqLeafTyVarLeft flav cv_given tv xi_unflat ; return (cc, ccs, co) } IdCo co -> return$ (CTyEqCan { cc_id = cv_given , cc_flavor = mkGivenFlavor gw UnkSkol , cc_tyvar = tv, cc_rhs = xi } -- xi, *not* xi_unflat because -- xi_unflat may require flattening! , emptyWorkList, co)  simonpj@microsoft.com committed Oct 07, 2010 876 877 878 879  ; case gw of Wanted {} -> setWantedCoBind cv co Derived {} -> setDerivedCoBind cv co _ -> pprPanic "Can't spontaneously solve *given*" empty  880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900  -- See Note [Avoid double unifications] ; return $Just (ct,cts) } -- ; let flav = mkGivenFlavor gw UnkSkol -- ; (cts, co) <- case coi of -- -- TODO: Optimise this, along the way it used to be -- ACo co -> do { cv_given <- newGivOrDerCoVar (mkTyVarTy tv) xi_unflat xi_unflat -- ; setWantedTyBind tv xi_unflat -- ; can_eqs <- canEq flav cv_given (mkTyVarTy tv) xi_unflat -- ; return (can_eqs, co) } -- IdCo co -> do { cv_given <- newGivOrDerCoVar (mkTyVarTy tv) xi xi -- ; setWantedTyBind tv xi -- ; can_eqs <- canEq flav cv_given (mkTyVarTy tv) xi -- ; return (can_eqs, co) } -- ; case gw of -- Wanted {} -> setWantedCoBind cv co -- Derived {} -> setDerivedCoBind cv co -- _ -> pprPanic "Can't spontaneously solve *given*" empty -- -- See Note [Avoid double unifications] -- ; return$ Just cts }  simonpj@microsoft.com committed Oct 07, 2010 901   simonpj@microsoft.com committed Oct 07, 2010 902 occurCheck :: VarEnv (TcTyVar, TcType) -> InertSet  simonpj@microsoft.com committed Oct 07, 2010 903 904 905 906 907 908 909 910 911 912  -> TcTyVar -> TcType -> Maybe (TcType,CoercionI) -- Traverse @ty@ to make sure that @tv@ does not appear under some flatten skolem. -- If it appears under some flatten skolem look in that flatten skolem equivalence class -- (see Note [InertSet FlattenSkolemEqClass], [Loopy Spontaneous Solving]) to see if you -- can find a different flatten skolem to use, that is, one that does not mention @tv@. -- -- Postcondition: Just (ty', coi) = occurCheck binds inerts tv ty -- coi :: ty' ~ ty -- NB: The returned type ty' may not be flat!  simonpj@microsoft.com committed Oct 07, 2010 913 914 occurCheck ty_binds inerts the_tv the_ty = ok emptyVarSet the_ty  simonpj@microsoft.com committed Oct 07, 2010 915  where  simonpj@microsoft.com committed Oct 07, 2010 916 917  -- If (fsk elem bad) then tv occurs in any rendering -- of the type under the expansion of fsk  simonpj@microsoft.com committed Oct 07, 2010 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938  ok bad this_ty@(TyConApp tc tys) | Just tys_cois <- allMaybes (map (ok bad) tys) , (tys',cois') <- unzip tys_cois = Just (TyConApp tc tys', mkTyConAppCoI tc cois') | isSynTyCon tc, Just ty_expanded <- tcView this_ty = ok bad ty_expanded -- See Note [Type synonyms and the occur check] in TcUnify ok bad (PredTy sty) | Just (sty',coi) <- ok_pred bad sty = Just (PredTy sty', coi) ok bad (FunTy arg res) | Just (arg', coiarg) <- ok bad arg, Just (res', coires) <- ok bad res = Just (FunTy arg' res', mkFunTyCoI coiarg coires) ok bad (AppTy fun arg) | Just (fun', coifun) <- ok bad fun, Just (arg', coiarg) <- ok bad arg = Just (AppTy fun' arg', mkAppTyCoI coifun coiarg) ok bad (ForAllTy tv1 ty1) -- WARNING: What if it is a (t1 ~ t2) => t3? It's not handled properly at the moment. | Just (ty1', coi) <- ok bad ty1 = Just (ForAllTy tv1 ty1', mkForAllTyCoI tv1 coi) -- Variable cases  simonpj@microsoft.com committed Oct 07, 2010 939 940 941 942 943 944  ok bad this_ty@(TyVarTy tv) | tv == the_tv = Nothing -- Occurs check error | not (isTcTyVar tv) = Just (this_ty, IdCo this_ty) -- Bound var | FlatSkol zty <- tcTyVarDetails tv = ok_fsk bad tv zty | Just (_,ty) <- lookupVarEnv ty_binds tv = ok bad ty | otherwise = Just (this_ty, IdCo this_ty)  simonpj@microsoft.com committed Oct 07, 2010 945 946 947 948 949  -- Check if there exists a ty bind already, as a result of sneaky unification. -- Fall through ok _bad _ty = Nothing  simonpj@microsoft.com committed Oct 07, 2010 950  -----------  simonpj@microsoft.com committed Oct 07, 2010 951 952 953 954 955 956 957 958 959 960 961 962  ok_pred bad (ClassP cn tys) | Just tys_cois <- allMaybes $map (ok bad) tys = let (tys', cois') = unzip tys_cois in Just (ClassP cn tys', mkClassPPredCoI cn cois') ok_pred bad (IParam nm ty) | Just (ty',co') <- ok bad ty = Just (IParam nm ty', mkIParamPredCoI nm co') ok_pred bad (EqPred ty1 ty2) | Just (ty1',coi1) <- ok bad ty1, Just (ty2',coi2) <- ok bad ty2 = Just (EqPred ty1' ty2', mkEqPredCoI coi1 coi2) ok_pred _ _ = Nothing  simonpj@microsoft.com committed Oct 07, 2010 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981  ----------- ok_fsk bad fsk zty | fsk elemVarSet bad -- We are already trying to find a rendering of fsk, -- and to do that it seems we need a rendering, so fail = Nothing | otherwise = firstJusts (ok new_bad zty : map (go_under_fsk new_bad) fsk_equivs) where fsk_equivs = getFskEqClass inerts fsk new_bad = bad extendVarSetList (fsk : map fst fsk_equivs) ----------- go_under_fsk bad_tvs (fsk,co) | FlatSkol zty <- tcTyVarDetails fsk = case ok bad_tvs zty of Nothing -> Nothing Just (ty,coi') -> Just (ty, mkTransCoI coi' (ACo co)) | otherwise = pprPanic "go_down_equiv" (ppr fsk)  simonpj@microsoft.com committed Sep 13, 2010 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 \end{code} ********************************************************************************* * * The interact-with-inert Stage * * ********************************************************************************* \begin{code} -- Interaction result of WorkItem <~> AtomicInert data InteractResult = IR { ir_stop :: StopOrContinue -- Stop -- => Reagent (work item) consumed. -- ContinueWith new_reagent -- => Reagent transformed but keep gathering interactions. -- The transformed item remains inert with respect -- to any previously encountered inerts. , ir_inert_action :: InertAction -- Whether the inert item should remain in the InertSet. , ir_new_work :: WorkList -- new work items to add to the WorkList  1007 1008  , ir_improvement :: Maybe FDImprovement -- In case improvement kicked in  simonpj@microsoft.com committed Sep 13, 2010 1009 1010 1011 1012 1013 1014 1015  } -- What to do with the inert reactant. data InertAction = KeepInert | DropInert deriving Eq mkIRContinue :: Monad m => WorkItem -> InertAction -> WorkList -> m InteractResult  1016 mkIRContinue wi keep newWork = return$ IR (ContinueWith wi) keep newWork Nothing  simonpj@microsoft.com committed Sep 13, 2010 1017 1018  mkIRStop :: Monad m => InertAction -> WorkList -> m InteractResult  1019 1020 1021 1022 1023 mkIRStop keep newWork = return $IR Stop keep newWork Nothing mkIRStop_RecordImprovement :: Monad m => InertAction -> WorkList -> FDImprovement -> m InteractResult mkIRStop_RecordImprovement keep newWork fdimpr = return$ IR Stop keep newWork (Just fdimpr)  simonpj@microsoft.com committed Sep 13, 2010 1024 dischargeWorkItem :: Monad m => m InteractResult  1025 dischargeWorkItem = mkIRStop KeepInert emptyWorkList  simonpj@microsoft.com committed Sep 13, 2010 1026 1027  noInteraction :: Monad m => WorkItem -> m InteractResult  1028 noInteraction workItem = mkIRContinue workItem KeepInert emptyWorkList  simonpj@microsoft.com committed Sep 13, 2010 1029   dimitris@microsoft.com committed Sep 23, 2010 1030 data WhichComesFromInert = LeftComesFromInert | RightComesFromInert  1031  -- See Note [Efficient Orientation, Case 2]  simonpj@microsoft.com committed Sep 13, 2010 1032   1033   simonpj@microsoft.com committed Sep 13, 2010 1034 ---------------------------------------------------  1035 1036 1037 1038 1039 1040 1041 1042 1043 -- Interact a single WorkItem with the equalities of an inert set as far as possible, i.e. until we -- get a Stop result from an individual reaction (i.e. when the WorkItem is consumed), or until we've -- interact the WorkItem with the entire equalities of the InertSet interactWithInertEqsStage :: SimplifierStage interactWithInertEqsStage workItem inert = foldISEqCtsM interactNext initITR inert where initITR = SR { sr_inerts = IS { inert_eqs = emptyCCan -- We will fold over the equalities , inert_fsks = Map.empty -- which will generate those two again  1044 1045 1046 1047  , inert_dicts = inert_dicts inert , inert_ips = inert_ips inert , inert_funeqs = inert_funeqs inert , inert_fds = inert_fds inert  1048 1049 1050 1051  } , sr_new_work = emptyWorkList , sr_stop = ContinueWith workItem }  simonpj@microsoft.com committed Sep 13, 2010 1052   1053 1054 1055 1056 --------------------------------------------------- -- Interact a single WorkItem with *non-equality* constraints in the inert set. -- Precondition: equality interactions must have already happened, hence we have -- to pick up some information from the incoming inert, before folding over the  1057 1058 -- "Other" constraints it contains!  simonpj@microsoft.com committed Sep 13, 2010 1059 1060 interactWithInertsStage :: SimplifierStage interactWithInertsStage workItem inert  1061 1062 1063 1064 1065  = let (relevant, inert_residual) = getISRelevant workItem inert initITR = SR { sr_inerts = inert_residual , sr_new_work = emptyWorkList , sr_stop = ContinueWith workItem } in Bag.foldlBagM interactNext initITR relevant  simonpj@microsoft.com committed Sep 13, 2010 1066  where  1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086  getISRelevant :: CanonicalCt -> InertSet -> (CanonicalCts, InertSet) getISRelevant (CDictCan { cc_class = cls } ) is = let (relevant, residual_map) = getRelevantCts cls (inert_dicts is) in (relevant, is { inert_dicts = residual_map }) getISRelevant (CFunEqCan { cc_fun = tc } ) is = let (relevant, residual_map) = getRelevantCts tc (inert_funeqs is) in (relevant, is { inert_funeqs = residual_map }) getISRelevant (CIPCan { cc_ip_nm = nm }) is = let (relevant, residual_map) = getRelevantCts nm (inert_ips is) in (relevant, is { inert_ips = residual_map }) -- An equality, finally, may kick everything except equalities out -- because we have already interacted the equalities in interactWithInertEqsStage getISRelevant _eq_ct is -- Equality, everything is relevant for this one -- TODO: if we were caching variables, we'd know that only -- some are relevant. Experiment with this for now. = let cts = cCanMapToBag (inert_ips is) unionBags cCanMapToBag (inert_dicts is) unionBags cCanMapToBag (inert_funeqs is) in (cts, is { inert_dicts = emptyCCanMap , inert_ips = emptyCCanMap , inert_funeqs = emptyCCanMap })  simonpj@microsoft.com committed Sep 13, 2010 1087   1088 1089 1090 interactNext :: StageResult -> AtomicInert -> TcS StageResult interactNext it inert | ContinueWith workItem <- sr_stop it  simonpj@microsoft.com committed Oct 19, 2010 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106  = do { let inerts = sr_inerts it fdimprs_old = getFDImprovements inerts ; ir <- interactWithInert fdimprs_old inert workItem -- New inerts depend on whether we KeepInert or not and must -- be updated with FD improvement information from the interaction result (ir) ; let inerts_new = updInertSetFDImprs upd_inert (ir_improvement ir) upd_inert = if ir_inert_action ir == KeepInert then inerts updInertSet inert else inerts ; return $SR { sr_inerts = inerts_new , sr_new_work = sr_new_work it unionWorkLists ir_new_work ir , sr_stop = ir_stop ir } } | otherwise = return$ it { sr_inerts = (sr_inerts it) updInertSet inert }  simonpj@microsoft.com committed Sep 13, 2010 1107 1108  -- Do a single interaction of two constraints.  1109 1110 interactWithInert :: FDImprovements -> AtomicInert -> WorkItem -> TcS InteractResult interactWithInert fdimprs inert workitem  simonpj@microsoft.com committed Sep 13, 2010 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122  = do { ctxt <- getTcSContext ; let is_allowed = allowedInteraction (simplEqsOnly ctxt) inert workitem inert_ev = cc_id inert work_ev = cc_id workitem -- Never interact a wanted and a derived where the derived's evidence -- mentions the wanted evidence in an unguarded way. -- See Note [Superclasses and recursive dictionaries] -- and Note [New Wanted Superclass Work] -- We don't have to do this for givens, as we fully know the evidence for them. ; rec_ev_ok <- case (cc_flavor inert, cc_flavor workitem) of  1123 1124 1125  (Wanted loc, Derived {}) -> isGoodRecEv work_ev (WantedEvVar inert_ev loc) (Derived {}, Wanted loc) -> isGoodRecEv inert_ev (WantedEvVar work_ev loc) _ -> return True  simonpj@microsoft.com committed Sep 13, 2010 1126 1127  ; if is_allowed && rec_ev_ok then  1128  doInteractWithInert fdimprs inert workitem  simonpj@microsoft.com committed Sep 13, 2010 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139  else noInteraction workitem } allowedInteraction :: Bool -> AtomicInert -> WorkItem -> Bool -- Allowed interactions allowedInteraction eqs_only (CDictCan {}) (CDictCan {}) = not eqs_only allowedInteraction eqs_only (CIPCan {}) (CIPCan {}) = not eqs_only allowedInteraction _ _ _ = True --------------------------------------------  1140 doInteractWithInert :: FDImprovements -> CanonicalCt -> CanonicalCt -> TcS InteractResult  simonpj@microsoft.com committed Sep 13, 2010 1141 1142 -- Identical class constraints.  1143 doInteractWithInert fdimprs  simonpj@microsoft.com committed Sep 13, 2010 1144 1145 1146 1147 1148 1149 1150  (CDictCan { cc_id = d1, cc_flavor = fl1, cc_class = cls1, cc_tyargs = tys1 }) workItem@(CDictCan { cc_id = d2, cc_flavor = fl2, cc_class = cls2, cc_tyargs = tys2 }) | cls1 == cls2 && (and $zipWith tcEqType tys1 tys2) = solveOneFromTheOther (d1,fl1) workItem | cls1 == cls2 && (not (isGiven fl1 && isGiven fl2)) = -- See Note [When improvement happens]  1151 1152 1153 1154  do { let pty1 = ClassP cls1 tys1 pty2 = ClassP cls2 tys2 work_item_pred_loc = (pty2, ppr d2) inert_pred_loc = (pty1, ppr d1)  simonpj@microsoft.com committed Sep 13, 2010 1155 1156  loc = combineCtLoc fl1 fl2 eqn_pred_locs = improveFromAnother work_item_pred_loc inert_pred_loc  1157   simonpj@microsoft.com committed Sep 13, 2010 1158  ; wevvars <- mkWantedFunDepEqns loc eqn_pred_locs  simonpj@microsoft.com committed Oct 20, 2010 1159  ; fd_work <- canWanteds wevvars  simonpj@microsoft.com committed Sep 13, 2010 1160  -- See Note [Generating extra equalities]  1161  ; traceTcS "Checking if improvements existed." (ppr fdimprs)  simonpj@microsoft.com committed Oct 20, 2010 1162  ; if isEmptyWorkList fd_work || haveBeenImproved fdimprs pty1 pty2 then  1163  -- Must keep going  1164  mkIRContinue workItem KeepInert fd_work  1165 1166  else do { traceTcS "Recording improvement and throwing item back in worklist." (ppr (pty1,pty2)) ; mkIRStop_RecordImprovement KeepInert  1167  (fd_work unionWorkLists workListFromCCan workItem) (pty1,pty2)  1168  }  1169  -- See Note [FunDep Reactions]  simonpj@microsoft.com committed Sep 13, 2010 1170 1171 1172 1173  } -- Class constraint and given equality: use the equality to rewrite -- the class constraint.  1174 1175 doInteractWithInert _fdimprs (CTyEqCan { cc_id = cv, cc_flavor = ifl, cc_tyvar = tv, cc_rhs = xi })  simonpj@microsoft.com committed Sep 13, 2010 1176 1177 1178  (CDictCan { cc_id = dv, cc_flavor = wfl, cc_class = cl, cc_tyargs = xis }) | ifl canRewrite wfl , tv elemVarSet tyVarsOfTypes xis  1179 1180 1181 1182 1183 1184  = if isDerivedSC wfl then mkIRStop KeepInert$ emptyWorkList -- See Note [Adding Derived Superclasses] else do { rewritten_dict <- rewriteDict (cv,tv,xi) (dv,wfl,cl,xis) -- Continue with rewritten Dictionary because we can only be in the -- interactWithEqsStage, so the dictionary is inert. ; mkIRContinue rewritten_dict KeepInert emptyWorkList }  simonpj@microsoft.com committed Sep 13, 2010 1185   1186 1187 doInteractWithInert _fdimprs (CDictCan { cc_id = dv, cc_flavor = ifl, cc_class = cl, cc_tyargs = xis })  simonpj@microsoft.com committed Sep 13, 2010 1188 1189 1190  workItem@(CTyEqCan { cc_id = cv, cc_flavor = wfl, cc_tyvar = tv, cc_rhs = xi }) | wfl canRewrite ifl , tv elemVarSet tyVarsOfTypes xis  1191 1192 1193 1194 1195  = if isDerivedSC ifl then mkIRContinue workItem DropInert emptyWorkList -- No need to do any rewriting, -- see Note [Adding Derived Superclasses] else do { rewritten_dict <- rewriteDict (cv,tv,xi) (dv,ifl,cl,xis) ; mkIRContinue workItem DropInert (workListFromCCan rewritten_dict) }  simonpj@microsoft.com committed Sep 13, 2010 1196 1197 1198  -- Class constraint and given equality: use the equality to rewrite -- the class constraint.  1199 1200 doInteractWithInert _fdimprs (CTyEqCan { cc_id = cv, cc_flavor = ifl, cc_tyvar = tv, cc_rhs = xi })  simonpj@microsoft.com committed Sep 13, 2010 1201 1202 1203 1204  (CIPCan { cc_id = ipid, cc_flavor = wfl, cc_ip_nm = nm, cc_ip_ty = ty }) | ifl canRewrite wfl , tv elemVarSet tyVarsOfType ty = do { rewritten_ip <- rewriteIP (cv,tv,xi) (ipid,wfl,nm,ty)  1205  ; mkIRContinue rewritten_ip KeepInert emptyWorkList }  simonpj@microsoft.com committed Sep 13, 2010 1206   1207 1208 doInteractWithInert _fdimprs (CIPCan { cc_id = ipid, cc_flavor = ifl, cc_ip_nm = nm, cc_ip_ty = ty })  simonpj@microsoft.com committed Sep 13, 2010 1209 1210 1211 1212  workItem@(CTyEqCan { cc_id = cv, cc_flavor = wfl, cc_tyvar = tv, cc_rhs = xi }) | wfl canRewrite ifl , tv elemVarSet tyVarsOfType ty = do { rewritten_ip <- rewriteIP (cv,tv,xi) (ipid,ifl,nm,ty)  1213  ; mkIRContinue workItem DropInert (workListFromCCan rewritten_ip) }  simonpj@microsoft.com committed Sep 13, 2010 1214 1215 1216 1217 1218 1219  -- Two implicit parameter constraints. If the names are the same, -- but their types are not, we generate a wanted type equality -- that equates the type (this is "improvement"). -- However, we don't actually need the coercion evidence, -- so we just generate a fresh coercion variable that isn't used anywhere.  1220 1221 doInteractWithInert _fdimprs (CIPCan { cc_id = id1, cc_flavor = ifl, cc_ip_nm = nm1, cc_ip_ty = ty1 })  simonpj@microsoft.com committed Sep 13, 2010 1222  workItem@(CIPCan { cc_flavor = wfl, cc_ip_nm = nm2, cc_ip_ty = ty2 })  simonpj@microsoft.com committed Sep 17, 2010 1223 1224 1225 1226  | nm1 == nm2 && isGiven wfl && isGiven ifl = -- See Note [Overriding implicit parameters] -- Dump the inert item, override totally with the new one -- Do not require type equality  1227  mkIRContinue workItem DropInert emptyWorkList  simonpj@microsoft.com committed Sep 17, 2010 1228   simonpj@microsoft.com committed Sep 13, 2010 1229 1230 1231  | nm1 == nm2 && ty1 tcEqType ty2 = solveOneFromTheOther (id1,ifl) workItem  simonpj@microsoft.com committed Sep 17, 2010 1232  | nm1 == nm2  simonpj@microsoft.com committed Sep 13, 2010 1233 1234 1235  = -- See Note [When improvement happens] do { co_var <- newWantedCoVar ty1 ty2 ; let flav = Wanted (combineCtLoc ifl wfl)  1236  ; cans <- mkCanonical flav co_var  simonpj@microsoft.com committed Oct 20, 2010 1237  ; mkIRContinue workItem KeepInert cans }  simonpj@microsoft.com committed Sep 13, 2010 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248  -- Inert: equality, work item: function equality -- Never rewrite a given with a wanted equality, and a type function -- equality can never rewrite an equality. Note also that if we have -- F x1 ~ x2 and a ~ x3, and a occurs in x2, we don't rewrite it. We -- can wait until F x1 ~ x2 matches another F x1 ~ x4, and only then -- we will expose'' x2 and x4 to rewriting. -- Otherwise, we can try rewriting the type function equality with the equality.  1249 1250 doInteractWithInert _fdimprs (CTyEqCan { cc_id = cv1, cc_flavor = ifl, cc_tyvar = tv, cc_rhs = xi1 })  simonpj@microsoft.com committed Sep 13, 2010 1251 1252 1253 1254 1255  (CFunEqCan { cc_id = cv2, cc_flavor = wfl, cc_fun = tc , cc_tyargs = args, cc_rhs = xi2 }) | ifl canRewrite wfl , tv elemVarSet tyVarsOfTypes args = do { rewritten_funeq <- rewriteFunEq (cv1,tv,xi1) (cv2,wfl,tc,args,xi2)  1256 1257  ; mkIRStop KeepInert (workListFromCCan rewritten_funeq) } -- must Stop here, because we may no longer be inert after the rewritting.  simonpj@microsoft.com committed Sep 13, 2010 1258 1259  -- Inert: function equality, work item: equality  1260 1261 doInteractWithInert _fdimprs (CFunEqCan {cc_id = cv1, cc_flavor = ifl, cc_fun = tc  simonpj@microsoft.com committed Sep 13, 2010 1262 1263 1264 1265 1266  , cc_tyargs = args, cc_rhs = xi1 }) workItem@(CTyEqCan { cc_id = cv2, cc_flavor = wfl, cc_tyvar = tv, cc_rhs = xi2 }) | wfl canRewrite ifl , tv elemVarSet tyVarsOfTypes args = do { rewritten_funeq <- rewriteFunEq (cv2,tv,xi2) (cv1,ifl,tc,args,xi1)  1267  ; mkIRContinue workItem DropInert (workListFromCCan rewritten_funeq) }  simonpj@microsoft.com committed Sep 13, 2010 1268   1269 1270 doInteractWithInert _fdimprs (CFunEqCan { cc_id = cv1, cc_flavor = fl1, cc_fun = tc1  simonpj@microsoft.com committed Sep 13, 2010 1271 1272 1273  , cc_tyargs = args1, cc_rhs = xi1 }) workItem@(CFunEqCan { cc_id = cv2, cc_flavor = fl2, cc_fun = tc2 , cc_tyargs = args2, cc_rhs = xi2 })  1274  | fl1 canSolve fl2 && lhss_match  dimitris@microsoft.com committed Sep 23, 2010 1275  = do { cans <- rewriteEqLHS LeftComesFromInert (mkCoVarCoercion cv1,xi1) (cv2,fl2,xi2)  simonpj@microsoft.com committed Oct 20, 2010 1276  ; mkIRStop KeepInert cans }  1277  | fl2 canSolve fl1 && lhss_match  dimitris@microsoft.com committed Sep 23, 2010 1278  = do { cans <- rewriteEqLHS RightComesFromInert (mkCoVarCoercion cv2,xi2) (cv1,fl1,xi1)  simonpj@microsoft.com committed Oct 20, 2010 1279  ; mkIRContinue workItem DropInert cans }  simonpj@microsoft.com committed Sep 13, 2010 1280 1281 1282  where lhss_match = tc1 == tc2 && and (zipWith tcEqType args1 args2)  1283 doInteractWithInert _fdimprs  dimitris@microsoft.com committed Oct 04, 2010 1284  inert@(CTyEqCan { cc_id = cv1, cc_flavor = fl1, cc_tyvar = tv1, cc_rhs = xi1 })  simonpj@microsoft.com committed Sep 13, 2010 1285 1286  workItem@(CTyEqCan { cc_id = cv2, cc_flavor = fl2, cc_tyvar = tv2, cc_rhs = xi2 }) -- Check for matching LHS  1287  | fl1 canSolve fl2 && tv1 == tv2  dimitris@microsoft.com committed Sep 23, 2010 1288  = do { cans <- rewriteEqLHS LeftComesFromInert (mkCoVarCoercion cv1,xi1) (cv2,fl2,xi2)  simonpj@microsoft.com committed Oct 20, 2010 1289  ; mkIRStop KeepInert cans }  simonpj@microsoft.com committed Sep 13, 2010 1290   1291  | fl2 canSolve fl1 && tv1 == tv2  dimitris@microsoft.com committed Sep 23, 2010 1292  = do { cans <- rewriteEqLHS RightComesFromInert (mkCoVarCoercion cv2,xi2) (cv1,fl1,xi1)  simonpj@microsoft.com committed Oct 20, 2010 1293  ; mkIRContinue workItem DropInert cans }  simonpj@microsoft.com committed Sep 13, 2010 1294 1295 1296 1297  -- Check for rewriting RHS | fl1 canRewrite fl2 && tv1 elemVarSet tyVarsOfType xi2 = do { rewritten_eq <- rewriteEqRHS (cv1,tv1,xi1) (cv2,fl2,tv2,xi2)  simonpj@microsoft.com committed Oct 20, 2010 1298  ; mkIRStop KeepInert rewritten_eq }  simonpj@microsoft.com committed Sep 13, 2010 1299 1300  | fl2 canRewrite fl1 && tv2 elemVarSet tyVarsOfType xi1 = do { rewritten_eq <- rewriteEqRHS (cv2,tv2,xi2) (cv1,fl1,tv1,xi1)  simonpj@microsoft.com committed Oct 20, 2010 1301  ; mkIRContinue workItem DropInert rewritten_eq }  dimitris@microsoft.com committed Oct 06, 2010 1302 1303 1304 1305 1306 1307  -- Finally, if workitem is a Flatten Equivalence Class constraint and the -- inert is a wanted constraint, even when the workitem cannot rewrite the -- inert, drop the inert out because you may have to reconsider solving the -- inert *using* the equivalence class you created. See note [Loopy Spontaneous Solving] -- and [InertSet FlattenSkolemEqClass]  dimitris@microsoft.com committed Oct 04, 2010 1308 1309 1310 1311 1312  | not $isGiven fl1, -- The inert is wanted or derived isMetaTyVar tv1, -- and has a unification variable lhs FlatSkol {} <- tcTyVarDetails tv2, -- And workitem is a flatten skolem equality Just tv2' <- tcGetTyVar_maybe xi2, FlatSkol {} <- tcTyVarDetails tv2'  1313  = mkIRContinue workItem DropInert (workListFromCCan inert)  simonpj@microsoft.com committed Sep 13, 2010 1314 1315   dimitris@microsoft.com committed Oct 06, 2010 1316 -- Fall-through case for all other situations  1317 doInteractWithInert _fdimprs _ workItem = noInteraction workItem  simonpj@microsoft.com committed Sep 13, 2010 1318   simonpj@microsoft.com committed Oct 08, 2010 1319 -------------------------  simonpj@microsoft.com committed Sep 13, 2010 1320 1321 1322 1323 1324 1325 1326 1327 1328 1329 1330 1331 1332 1333 1334 1335 1336 1337 1338 1339 1340 1341 1342 1343 1344 1345 1346 1347 1348 1349 1350 1351 1352 1353 1354 1355 1356 1357 1358 1359 1360 1361 1362 1363 1364 1365 1366 1367 -- Equational Rewriting rewriteDict :: (CoVar, TcTyVar, Xi) -> (DictId, CtFlavor, Class, [Xi]) -> TcS CanonicalCt rewriteDict (cv,tv,xi) (dv,gw,cl,xis) = do { let cos = substTysWith [tv] [mkCoVarCoercion cv] xis -- xis[tv] ~ xis[xi] args = substTysWith [tv] [xi] xis con = classTyCon cl dict_co = mkTyConCoercion con cos ; dv' <- newDictVar cl args ; case gw of Wanted {} -> setDictBind dv (EvCast dv' (mkSymCoercion dict_co)) _given_or_derived -> setDictBind dv' (EvCast dv dict_co) ; return (CDictCan { cc_id = dv' , cc_flavor = gw , cc_class = cl , cc_tyargs = args }) } rewriteIP :: (CoVar,TcTyVar,Xi) -> (EvVar,CtFlavor, IPName Name, TcType) -> TcS CanonicalCt rewriteIP (cv,tv,xi) (ipid,gw,nm,ty) = do { let ip_co = substTyWith [tv] [mkCoVarCoercion cv] ty -- ty[tv] ~ t[xi] ty' = substTyWith [tv] [xi] ty ; ipid' <- newIPVar nm ty' ; case gw of Wanted {} -> setIPBind ipid (EvCast ipid' (mkSymCoercion ip_co)) _given_or_derived -> setIPBind ipid' (EvCast ipid ip_co) ; return (CIPCan { cc_id = ipid' , cc_flavor = gw , cc_ip_nm = nm , cc_ip_ty = ty' }) } rewriteFunEq :: (CoVar,TcTyVar,Xi) -> (CoVar,CtFlavor,TyCon, [Xi], Xi) -> TcS CanonicalCt rewriteFunEq (cv1,tv,xi1) (cv2,gw, tc,args,xi2) = do { let arg_cos = substTysWith [tv] [mkCoVarCoercion cv1] args args' = substTysWith [tv] [xi1] args fun_co = mkTyConCoercion tc arg_cos ; cv2' <- case gw of Wanted {} -> do { cv2' <- newWantedCoVar (mkTyConApp tc args') xi2 ; setWantedCoBind cv2$ mkTransCoercion fun_co (mkCoVarCoercion cv2') ; return cv2' } _giv_or_der -> newGivOrDerCoVar (mkTyConApp tc args') xi2 $mkTransCoercion (mkSymCoercion fun_co) (mkCoVarCoercion cv2) ; return (CFunEqCan { cc_id = cv2' , cc_flavor = gw , cc_tyargs = args' , cc_fun = tc , cc_rhs = xi2 }) }  simonpj@microsoft.com committed Oct 20, 2010 1368 rewriteEqRHS :: (CoVar,TcTyVar,Xi) -> (CoVar,CtFlavor,TcTyVar,Xi) -> TcS WorkList  simonpj@microsoft.com committed Sep 13, 2010 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 1380 1381 1382 1383 1384 1385 1386 1387 1388 1389 1390 1391 1392 -- Use the first equality to rewrite the second, flavors already checked. -- E.g. c1 : tv1 ~ xi1 c2 : tv2 ~ xi2 -- rewrites c2 to give -- c2' : tv2 ~ xi2[xi1/tv1] -- We must do an occurs check to sure the new constraint is canonical -- So we might return an empty bag rewriteEqRHS (cv1,tv1,xi1) (cv2,gw,tv2,xi2) | Just tv2' <- tcGetTyVar_maybe xi2' , tv2 == tv2' -- In this case xi2[xi1/tv1] = tv2, so we have tv2~tv2 = do { when (isWanted gw) (setWantedCoBind cv2 (mkSymCoercion co2')) ; return emptyCCan } | otherwise = do { cv2' <- case gw of Wanted {} -> do { cv2' <- newWantedCoVar (mkTyVarTy tv2) xi2' ; setWantedCoBind cv2$ mkCoVarCoercion cv2' mkTransCoercion mkSymCoercion co2' ; return cv2' } _giv_or_der -> newGivOrDerCoVar (mkTyVarTy tv2) xi2' $mkCoVarCoercion cv2 mkTransCoercion co2' ; xi2'' <- canOccursCheck gw tv2 xi2' -- we know xi2' is *not* tv2  1393  ; canEq gw cv2' (mkTyVarTy tv2) xi2''  simonpj@microsoft.com committed Sep 13, 2010 1394 1395 1396 1397 1398  } where xi2' = substTyWith [tv1] [xi1] xi2 co2' = substTyWith [tv1] [mkCoVarCoercion cv1] xi2 -- xi2 ~ xi2[xi1/tv1]  dimitris@microsoft.com committed Sep 23, 2010 1399   simonpj@microsoft.com committed Oct 20, 2010 1400 rewriteEqLHS :: WhichComesFromInert -> (Coercion,Xi) -> (CoVar,CtFlavor,Xi) -> TcS WorkList  1401 -- Used to ineract two equalities of the following form:  simonpj@microsoft.com committed Sep 13, 2010 1402 1403 -- First Equality: co1: (XXX ~ xi1) -- Second Equality: cv2: (XXX ~ xi2)  1404 -- Where the cv1 canSolve cv2 equality  1405 1406 -- We have an option of creating new work (xi1 ~ xi2) OR (xi2 ~ xi1), -- See Note [Efficient Orientation] for that  dimitris@microsoft.com committed Sep 23, 2010 1407 1408 1409 1410 1411 1412 1413 1414 1415 1416 1417 1418 1419 1420 1421 1422 1423 1424 rewriteEqLHS which (co1,xi1) (cv2,gw,xi2) = do { cv2' <- case (isWanted gw, which) of (True,LeftComesFromInert) -> do { cv2' <- newWantedCoVar xi2 xi1 ; setWantedCoBind cv2$ co1 mkTransCoercion mkSymCoercion (mkCoVarCoercion cv2') ; return cv2' } (True,RightComesFromInert) ->