TcInteract.lhs 88.3 KB
 simonpj@microsoft.com committed Sep 13, 2010 1 \begin{code}  Ian Lynagh committed Nov 04, 2011 2 3 4 5 6 7 8 {-# OPTIONS -fno-warn-tabs #-} -- The above warning supression flag is a temporary kludge. -- While working on this module you are encouraged to remove it and -- detab the module (please do the detabbing in a separate patch). See -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#TabsvsSpaces -- for details  simonpj@microsoft.com committed Sep 13, 2010 9 module TcInteract (  dimitris committed Nov 16, 2011 10 11  solveInteractGiven, -- Solves [EvVar],GivenLoc solveInteractCts, -- Solves [Cts]  simonpj@microsoft.com committed Sep 13, 2010 12 13 14 15  ) where #include "HsVersions.h"  dimitris@microsoft.com committed Oct 04, 2010 16   dimitris committed Nov 16, 2011 17 import BasicTypes ()  simonpj@microsoft.com committed Sep 13, 2010 18 19 20 import TcCanonical import VarSet import Type  dimitris committed May 17, 2011 21 import Unify  Simon Peyton Jones committed Jan 03, 2012 22 23 import FamInstEnv import Coercion( mkAxInstRHS )  simonpj@microsoft.com committed Sep 13, 2010 24 25 26 27 28  import Id import Var import TcType  Iavor S. Diatchki committed Jan 24, 2012 29 import PrelNames (typeNatClassName, typeStringClassName)  simonpj@microsoft.com committed Sep 13, 2010 30   simonpj@microsoft.com committed Nov 12, 2010 31 32 import Class import TyCon  simonpj@microsoft.com committed Sep 13, 2010 33 import Name  dimitris committed Nov 16, 2011 34 import IParam  simonpj@microsoft.com committed Sep 13, 2010 35   dimitris committed Mar 28, 2012 36 import TysWiredIn ( eqTyCon )  simonpj@microsoft.com committed Sep 13, 2010 37 38 import FunDeps  Simon Peyton Jones committed Dec 05, 2011 39 import TcEvidence  simonpj@microsoft.com committed Sep 13, 2010 40 41 import Outputable  dimitris committed Dec 22, 2011 42 43 import TcMType ( zonkTcPredType )  simonpj@microsoft.com committed Nov 12, 2010 44 import TcRnTypes  simonpj@microsoft.com committed Sep 13, 2010 45 import TcErrors  simonpj@microsoft.com committed Nov 12, 2010 46 import TcSMonad  Simon Peyton Jones committed Jun 22, 2011 47 import Maybes( orElse )  simonpj@microsoft.com committed Oct 07, 2010 48 import Bag  dimitris@microsoft.com committed Oct 04, 2010 49   dimitris committed Nov 16, 2011 50 51 52 import Control.Monad ( foldM ) import TrieMap  dimitris committed Nov 28, 2011 53 54 55 import VarEnv import qualified Data.Traversable as Traversable  simonpj@microsoft.com committed Jan 12, 2011 56 import Control.Monad( when )  dimitris committed Nov 28, 2011 57 import Pair ( pSnd )  Simon Peyton Jones committed Jul 29, 2011 58 import UniqFM  simonpj@microsoft.com committed Sep 13, 2010 59 60 61 import FastString ( sLit ) import DynFlags \end{code}  dimitris committed Nov 16, 2011 62 63 ********************************************************************** * *  simonpj@microsoft.com committed Sep 13, 2010 64 65 66 67 * Main Interaction Solver * * * **********************************************************************  dimitris committed Nov 16, 2011 68 69 Note [Basic Simplifier Plan] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~  70   dimitris committed Nov 16, 2011 71 72 1. Pick an element from the WorkList if there exists one with depth less thanour context-stack depth.  simonpj@microsoft.com committed Sep 13, 2010 73   dimitris committed Nov 16, 2011 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 2. Run it down the 'stage' pipeline. Stages are: - canonicalization - inert reactions - spontaneous reactions - top-level intreactions Each stage returns a StopOrContinue and may have sideffected the inerts or worklist. The threading of the stages is as follows: - If (Stop) is returned by a stage then we start again from Step 1. - If (ContinueWith ct) is returned by a stage, we feed 'ct' on to the next stage in the pipeline. 4. If the element has survived (i.e. ContinueWith x) the last stage then we add him in the inerts and jump back to Step 1. If in Step 1 no such element exists, we have exceeded our context-stack depth and will simply fail.  simonpj@microsoft.com committed Sep 13, 2010 91 92 \begin{code}  dimitris committed Nov 16, 2011 93 94 solveInteractCts :: [Ct] -> TcS () solveInteractCts cts  dimitris committed Mar 28, 2012 95 96 97 98  = do { traceTcS "solveInteractCtS" (vcat [ text "cts =" <+> ppr cts ]) ; updWorkListTcS (appendWorkListCt cts) >> solveInteract } {- DELETEME  dimitris committed Nov 16, 2011 99 100 101 102 103 104 105 106  = do { evvar_cache <- getTcSEvVarCacheMap ; (cts_thinner, new_evvar_cache) <- add_cts_in_cache evvar_cache cts ; traceTcS "solveInteractCts" (vcat [ text "cts_original =" <+> ppr cts, text "cts_thinner =" <+> ppr cts_thinner ]) ; setTcSEvVarCacheMap new_evvar_cache ; updWorkListTcS (appendWorkListCt cts_thinner) >> solveInteract }  Simon Peyton Jones committed Jan 17, 2012 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144  where add_cts_in_cache evvar_cache cts = do { ctxt <- getTcSContext ; foldM (solve_or_cache (simplEqsOnly ctxt)) ([],evvar_cache) cts } solve_or_cache :: Bool -- Solve equalities only, not classes etc -> ([Ct],TypeMap (EvVar,CtFlavor)) -> Ct -> TcS ([Ct],TypeMap (EvVar,CtFlavor)) solve_or_cache eqs_only (acc_cts,acc_cache) ct | dont_cache eqs_only (classifyPredType pred_ty) = return (ct:acc_cts,acc_cache) | Just (ev',fl') <- lookupTM pred_ty acc_cache , fl' canSolve fl , isWanted fl = do { _ <- setEvBind ev (EvId ev') fl ; return (acc_cts,acc_cache) } | otherwise -- If it's a given keep it in the work list, even if it exists in the cache! = return (ct:acc_cts, alterTM pred_ty (\_ -> Just (ev,fl)) acc_cache) where fl = cc_flavor ct ev = cc_id ct pred_ty = ctPred ct dont_cache :: Bool -> PredTree -> Bool -- Do not use the cache, not update it, if this is true dont_cache _ (IPPred {}) = True -- IPPreds have subtle shadowing dont_cache _ (EqPred ty1 ty2) -- Report Int ~ Bool errors separately | Just tc1 <- tyConAppTyCon_maybe ty1 , Just tc2 <- tyConAppTyCon_maybe ty2 , tc1 /= tc2 = isDecomposableTyCon tc1 && isDecomposableTyCon tc2 | otherwise = False dont_cache eqs_only _ = eqs_only -- If we are simplifying equalities only, -- do not cache non-equalities -- See Note [Simplifying RULE lhs constraints] in TcSimplify  dimitris committed Mar 28, 2012 145 -}  dimitris committed Nov 16, 2011 146 147 148 149  solveInteractGiven :: GivenLoc -> [EvVar] -> TcS () solveInteractGiven gloc evs = solveInteractCts (map mk_noncan evs)  dimitris committed Mar 28, 2012 150  where mk_noncan ev = CNonCanonical { cc_flavor = Given gloc ev  dimitris committed Nov 16, 2011 151 152 153 154 155 156 157  , cc_depth = 0 } -- The main solver loop implements Note [Basic Simplifier Plan] --------------------------------------------------------------- solveInteract :: TcS () -- Returns the final InertSet in TcS, WorkList will be eventually empty. solveInteract  dimitris committed Nov 28, 2011 158 159  = {-# SCC "solveInteract" #-} do { dyn_flags <- getDynFlags  dimitris committed Nov 16, 2011 160 161  ; let max_depth = ctxtStkDepth dyn_flags solve_loop  dimitris committed Nov 28, 2011 162 163  = {-# SCC "solve_loop" #-} do { sel <- selectNextWorkItem max_depth  dimitris committed Nov 16, 2011 164 165 166 167  ; case sel of NoWorkRemaining -- Done, successfuly (modulo frozen) -> return () MaxDepthExceeded ct -- Failure, depth exceeded  Simon Peyton Jones committed Jan 12, 2012 168  -> wrapErrTcS $solverDepthErrorTcS (cc_depth ct) [ct]  dimitris committed Nov 16, 2011 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188  NextWorkItem ct -- More work, loop around! -> runSolverPipeline thePipeline ct >> solve_loop } ; solve_loop } type WorkItem = Ct type SimplifierStage = WorkItem -> TcS StopOrContinue continueWith :: WorkItem -> TcS StopOrContinue continueWith work_item = return (ContinueWith work_item) data SelectWorkItem = NoWorkRemaining -- No more work left (effectively we're done!) | MaxDepthExceeded Ct -- More work left to do but this constraint has exceeded -- the max subgoal depth and we must stop | NextWorkItem Ct -- More work left, here's the next item to look at selectNextWorkItem :: SubGoalDepth -- Max depth allowed -> TcS SelectWorkItem selectNextWorkItem max_depth = updWorkListTcS_return pick_next  simonpj@microsoft.com committed Sep 13, 2010 189  where  dimitris committed Nov 16, 2011 190  pick_next :: WorkList -> (SelectWorkItem, WorkList)  dimitris committed Nov 28, 2011 191 192 193 194 195 196 197 198  pick_next wl = case selectWorkItem wl of (Nothing,_) -> (NoWorkRemaining,wl) -- No more work (Just ct, new_wl) | cc_depth ct > max_depth -- Depth exceeded -> (MaxDepthExceeded ct,new_wl) (Just ct, new_wl) -> (NextWorkItem ct, new_wl) -- New workitem and worklist  dimitris committed Nov 16, 2011 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231  runSolverPipeline :: [(String,SimplifierStage)] -- The pipeline -> WorkItem -- The work item -> TcS () -- Run this item down the pipeline, leaving behind new work and inerts runSolverPipeline pipeline workItem = do { initial_is <- getTcSInerts ; traceTcS "Start solver pipeline {"$ vcat [ ptext (sLit "work item = ") <+> ppr workItem , ptext (sLit "inerts = ") <+> ppr initial_is] ; final_res <- run_pipeline pipeline (ContinueWith workItem) ; final_is <- getTcSInerts ; case final_res of Stop -> do { traceTcS "End solver pipeline (discharged) }" (ptext (sLit "inerts = ") <+> ppr final_is) ; return () } ContinueWith ct -> do { traceTcS "End solver pipeline (not discharged) }" $vcat [ ptext (sLit "final_item = ") <+> ppr ct , ptext (sLit "inerts = ") <+> ppr final_is] ; updInertSetTcS ct } } where run_pipeline :: [(String,SimplifierStage)] -> StopOrContinue -> TcS StopOrContinue run_pipeline [] res = return res run_pipeline _ Stop = return Stop run_pipeline ((stg_name,stg):stgs) (ContinueWith ct) = do { traceTcS ("runStage " ++ stg_name ++ " {") (text "workitem = " <+> ppr ct) ; res <- stg ct ; traceTcS ("end stage " ++ stg_name ++ " }") empty ; run_pipeline stgs res }  simonpj@microsoft.com committed Sep 13, 2010 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 \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}  dimitris committed Nov 16, 2011 258 259 260 261 262 thePipeline :: [(String,SimplifierStage)] thePipeline = [ ("canonicalization", canonicalizationStage) , ("spontaneous solve", spontaneousSolveStage) , ("interact with inerts", interactWithInertsStage) , ("top-level reactions", topReactionsStage) ]  dimitris@microsoft.com committed Dec 09, 2010 263 264 265 266 \end{code} \begin{code}  simonpj@microsoft.com committed Sep 13, 2010 267   dimitris committed Mar 28, 2012 268   dimitris committed Nov 16, 2011 269 270 271 272 -- The canonicalization stage, see TcCanonical for details ---------------------------------------------------------- canonicalizationStage :: SimplifierStage canonicalizationStage = TcCanonical.canonicalize  simonpj@microsoft.com committed Oct 20, 2010 273   simonpj@microsoft.com committed Sep 13, 2010 274 275 276 277 278 279 280 281 \end{code} ********************************************************************************* * * The spontaneous-solve Stage * * *********************************************************************************  282 283 284 285 286 287 Note [Efficient Orientation] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ There are two cases where we have to be careful about orienting equalities to get better efficiency.  simonpj@microsoft.com committed Nov 12, 2010 288 Case 1: In Rewriting Equalities (function rewriteEqLHS)  289   290 291 292 293 294 295 296 297 298 299  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.  300   simonpj@microsoft.com committed Nov 12, 2010 301 302 303 304 305 Case 2: Functional Dependencies Again, we should prefer, if possible, the inert variables on the RHS Case 3: IP improvement work We must always rewrite so that the inert type is on the right.  306   simonpj@microsoft.com committed Sep 13, 2010 307 308 \begin{code} spontaneousSolveStage :: SimplifierStage  dimitris committed Nov 16, 2011 309 spontaneousSolveStage workItem  simonpj@microsoft.com committed Nov 12, 2010 310  = do { mSolve <- trySpontaneousSolve workItem  dimitris committed Nov 16, 2011 311  ; spont_solve mSolve }  dimitris committed Nov 28, 2011 312 313 314 315 316 317 318  where spont_solve SPCantSolve | isCTyEqCan workItem -- Unsolved equality = do { kickOutRewritableInerts workItem -- NB: will add workItem in inerts ; return Stop } | otherwise = continueWith workItem spont_solve (SPSolved workItem') -- Post: workItem' must be equality  dimitris committed Nov 16, 2011 319 320 321 322  = do { bumpStepCountTcS ; traceFireTcS (cc_depth workItem)$ ptext (sLit "Spontaneous") <+> parens (ppr (cc_flavor workItem)) <+> ppr workItem  dimitris committed Nov 28, 2011 323 324 325 326  -- NB: will add the item in the inerts ; kickOutRewritableInerts workItem' -- .. and Stop  dimitris committed Nov 16, 2011 327 328 329 330  ; return Stop } kickOutRewritableInerts :: Ct -> TcS () -- Pre: ct is a CTyEqCan  dimitris committed Nov 28, 2011 331 332 333 -- Post: The TcS monad is left with the thinner non-rewritable inerts; but which -- contains the new constraint. -- The rewritable end up in the worklist  dimitris committed Nov 28, 2011 334 kickOutRewritableInerts ct  dimitris committed Nov 28, 2011 335  = {-# SCC "kickOutRewritableInerts" #-}  dimitris committed Mar 28, 2012 336 337  do { traceTcS "kickOutRewritableInerts" $text "workitem = " <+> ppr ct ; (wl,ieqs) <- {-# SCC "kick_out_rewritable" #-}  dimitris committed Nov 28, 2011 338  modifyInertTcS (kick_out_rewritable ct)  dimitris committed Mar 28, 2012 339 340 341  ; traceTcS "Kicked out the following constraints"$ ppr wl ; is <- getTcSInerts ; traceTcS "Remaining inerts are" $ppr is  dimitris committed Nov 28, 2011 342   dimitris committed Mar 28, 2012 343 344 345 346 347  -- Step 1: Rewrite as many of the inert_eqs on the spot! -- NB: if it is a given constraint just use the cached evidence -- to optimize e.g. mkRefl coercions from spontaneously solved cts. ; bnds <- getTcEvBindsMap ; let ct_coercion = getCtCoercion bnds ct  dimitris committed Nov 28, 2011 348 349  ; new_ieqs <- {-# SCC "rewriteInertEqsFromInertEq" #-}  dimitris committed Mar 28, 2012 350 351 352 353 354 355 356 357 358 359 360  rewriteInertEqsFromInertEq (cc_tyvar ct, ct_coercion,cc_flavor ct) ieqs ; let upd_eqs is = is { inert_cans = new_ics } where ics = inert_cans is new_ics = ics { inert_eqs = new_ieqs } ; modifyInertTcS (\is -> ((), upd_eqs is)) ; is <- getTcSInerts ; traceTcS "Final inerts are"$ ppr is -- Step 2: Add the new guy in  dimitris committed Nov 28, 2011 361  ; updInertSetTcS ct  dimitris committed Nov 16, 2011 362 363 364  ; traceTcS "Kick out" (ppr ct  ppr wl) ; updWorkListTcS (unionWorkList wl) }  dimitris committed Nov 28, 2011 365   Simon Peyton Jones committed Dec 05, 2011 366 rewriteInertEqsFromInertEq :: (TcTyVar, TcCoercion, CtFlavor) -- A new substitution  dimitris committed Mar 28, 2012 367 368  -> TyVarEnv Ct -- All the inert equalities -> TcS (TyVarEnv Ct) -- The new inert equalities  Simon Peyton Jones committed Dec 05, 2011 369 rewriteInertEqsFromInertEq (subst_tv, subst_co, subst_fl) ieqs  dimitris committed Nov 28, 2011 370 371 372 373 374 -- The goal: traverse the inert equalities and rewrite some of them, dropping some others -- back to the worklist. This is delicate, see Note [Delicate equality kick-out] = do { mieqs <- Traversable.mapM do_one ieqs ; traceTcS "Original inert equalities:" (ppr ieqs) ; let flatten_justs elem venv  dimitris committed Mar 28, 2012 375  | Just act <- elem = extendVarEnv venv (cc_tyvar act) act  dimitris committed Nov 28, 2011 376 377 378 379  | otherwise = venv final_ieqs = foldVarEnv flatten_justs emptyVarEnv mieqs ; traceTcS "Remaining inert equalities:" (ppr final_ieqs) ; return final_ieqs }  dimitris committed Nov 28, 2011 380   dimitris committed Mar 28, 2012 381  where do_one ct  dimitris committed Nov 28, 2011 382  | subst_fl canRewrite fl && (subst_tv elemVarSet tyVarsOfCt ct)  dimitris committed Mar 28, 2012 383 384 385  -- Annoyingly inefficient, but we can't simply check -- that isReflCo co because of cached solved ReflCo evidence. = if fl canRewrite subst_fl then  dimitris committed Nov 28, 2011 386 387  -- If also the inert can rewrite the subst it's totally safe -- to rewrite on the spot  dimitris committed Mar 28, 2012 388 389  do { ct' <- rewrite_on_the_spot ct ; return $Just ct' }  dimitris committed Nov 28, 2011 390 391 392 393  else -- We have to throw inert back to worklist for occurs checks do { updWorkListTcS (extendWorkListEq ct) ; return Nothing } | otherwise -- Just keep it there  dimitris committed Mar 28, 2012 394  = return$ Just ct  dimitris committed Nov 28, 2011 395  where  dimitris committed Mar 28, 2012 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424  -- We have that: subst_co :: subst_tv ~ tau -- An an old inert: tv ~ rhs -- That we want to rewrite on-the-spot to tv ~ rhs[tau/subst_tv] fl = cc_flavor ct tv = cc_tyvar ct rhs = cc_rhs ct rewrite_on_the_spot ct = do { let rhs_co = liftTcCoSubstWith [subst_tv] [subst_co] rhs eq_co = mkTcTyConAppCo eqTyCon $[ mkTcReflCo (typeKind rhs) , mkTcReflCo (mkTyVarTy tv) , mkTcSymCo rhs_co ] new_rhs = pSnd (tcCoercionKind rhs_co) new_eq_pred = mkTcEqPred (mkTyVarTy tv) new_rhs -- eq_co :: (tv ~ rhs[s/x]) ~ (tv ~ rhs[x]) ; mb_fl <- rewriteCtFlavor fl new_eq_pred eq_co ; case mb_fl of Just new_fl -> return$ ct {cc_flavor=new_fl,cc_rhs=new_rhs} Nothing -> -- Weird, rewritten constraint was solved -- before -- I am uncertain about what to do pprPanic "Interesting: \ rewrote inert equality to existing!" $vcat [ text "original ="<+>ppr ct , text "new eqpred ="<+>ppr new_eq_pred ] } {- DELETEME  Simon Peyton Jones committed Dec 05, 2011 425  = do { let rhs' = pSnd (tcCoercionKind co)  dimitris committed Nov 28, 2011 426 427  ; delCachedEvVar ev fl ; evc <- newEqVar fl (mkTyVarTy tv) rhs'  Simon Peyton Jones committed Dec 05, 2011 428 429  ; let ev' = evc_the_evvar evc ; let evco' = mkTcCoVarCo ev'  dimitris committed Nov 28, 2011 430 431 432  ; fl' <- if isNewEvVar evc then do { case fl of Wanted {}  Simon Peyton Jones committed Dec 05, 2011 433  -> setEqBind ev (evco' mkTcTransCo mkTcSymCo co) fl  dimitris committed Nov 28, 2011 434  Given {}  Simon Peyton Jones committed Dec 05, 2011 435  -> setEqBind ev' (mkTcCoVarCo ev mkTcTransCo co) fl  dimitris committed Nov 28, 2011 436 437 438 439  Derived {} -> return fl } else if isWanted fl then  Simon Peyton Jones committed Dec 05, 2011 440  setEqBind ev (evco' mkTcTransCo mkTcSymCo co) fl  dimitris committed Nov 28, 2011 441 442 443 444  else return fl ; let ct' = ct { cc_id = ev', cc_flavor = fl', cc_rhs = rhs' } ; return (ct',evco') } ev = cc_id ct  dimitris committed Mar 28, 2012 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 -} kick_out_rewritable :: Ct -> InertSet -> ((WorkList, TyVarEnv Ct),InertSet) -- Post: returns ALL inert equalities, to be dealt with later -- kick_out_rewritable ct is@(IS { inert_cans = IC { inert_eqs = eqmap , inert_eq_tvs = inscope , inert_dicts = dictmap , inert_ips = ipmap , inert_funeqs = funeqmap , inert_irreds = irreds } , inert_frozen = frozen }) = ((kicked_out,eqmap), remaining)  dimitris committed Nov 16, 2011 461  where  dimitris committed Nov 28, 2011 462  kicked_out = WorkList { wl_eqs = []  dimitris committed Nov 28, 2011 463 464 465  , wl_funeqs = bagToList feqs_out , wl_rest = bagToList (fro_out andCts dicts_out andCts ips_out andCts irs_out) }  dimitris committed Nov 16, 2011 466   dimitris committed Mar 28, 2012 467 468 469 470 471 472 473 474 475 476 477 478  remaining = is { inert_cans = IC { inert_eqs = emptyVarEnv , inert_eq_tvs = inscope -- keep the same, safe and cheap , inert_dicts = dicts_in , inert_ips = ips_in , inert_funeqs = feqs_in , inert_irreds = irs_in } , inert_frozen = fro_in } -- NB: Notice that don't rewrite -- inert_solved, inert_flat_cache and inert_solved_funeqs -- optimistically. But when we lookup we have to take the -- subsitution into account  dimitris committed Nov 16, 2011 479 480  fl = cc_flavor ct tv = cc_tyvar ct  dimitris committed Nov 28, 2011 481 482  (ips_out, ips_in) = partitionCCanMap rewritable ipmap  dimitris committed Nov 16, 2011 483   dimitris committed Mar 28, 2012 484  (feqs_out, feqs_in) = partCtFamHeadMap rewritable funeqmap  dimitris committed Nov 28, 2011 485  (dicts_out, dicts_in) = partitionCCanMap rewritable dictmap  dimitris committed Nov 16, 2011 486 487 488  (irs_out, irs_in) = partitionBag rewritable irreds (fro_out, fro_in) = partitionBag rewritable frozen  dimitris committed Nov 28, 2011 489 490  rewritable ct = (fl canRewrite cc_flavor ct) &&  dimitris committed Dec 22, 2011 491 492 493 494 495 496 497 498 499 500  (tv elemVarSet tyVarsOfCt ct) -- NB: tyVarsOfCt will return the type -- variables /and the kind variables/ that are -- directly visible in the type. Hence we will -- have exposed all the rewriting we care about -- to make the most precise kinds visible for -- matching classes etc. No need to kick out -- constraints that mention type variables whose -- kinds could contain this variable!  dimitris committed Nov 28, 2011 501 \end{code}  dimitris committed Nov 16, 2011 502   dimitris committed Nov 28, 2011 503 504 Note [Delicate equality kick-out] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  dimitris committed Nov 28, 2011 505   dimitris committed Nov 28, 2011 506 507 508 509 510 Delicate: When kicking out rewritable constraints, it would be safe to simply kick out all rewritable equalities, but instead we only kick out those that, when rewritten, may result in occur-check errors. We rewrite the rest on the spot. Example:  dimitris committed Nov 16, 2011 511   dimitris committed Nov 28, 2011 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529  WorkItem = [S] a ~ b Inerts = { [W] b ~ [a] } Now at this point the work item cannot be further rewritten by the inert (due to the weaker inert flavor), so we are examining if we can instead rewrite the inert from the workitem. But if we rewrite it on the spot we have to recanonicalize because of the danger of occurs errors. On the other hand if the inert flavor was just as powerful or more powerful than the workitem flavor, the work-item could not have reached this stage (because it would have already been rewritten by the inert). The coclusion is: we kick out the 'dangerous' equalities that may require recanonicalization (occurs checks) and the rest we rewrite unconditionally without further checks, on-the-spot with function rewriteInertEqsFromInertEq. \begin{code}  dimitris committed Nov 16, 2011 530 531 data SPSolveResult = SPCantSolve | SPSolved WorkItem  dimitris@microsoft.com committed Oct 06, 2010 532   simonpj@microsoft.com committed Nov 12, 2010 533 534 535 -- SPCantSolve means that we can't do the unification because e.g. the variable is untouchable -- SPSolved workItem' gives us a new *given* to go on  simonpj@microsoft.com committed Sep 13, 2010 536 -- @trySpontaneousSolve wi@ solves equalities where one side is a  simonpj@microsoft.com committed Nov 12, 2010 537 -- touchable unification variable.  simonpj@microsoft.com committed Sep 13, 2010 538 -- See Note [Touchables and givens]  simonpj@microsoft.com committed Nov 12, 2010 539 trySpontaneousSolve :: WorkItem -> TcS SPSolveResult  dimitris committed Mar 28, 2012 540 trySpontaneousSolve workItem@(CTyEqCan { cc_flavor = gw  dimitris committed Nov 16, 2011 541  , cc_tyvar = tv1, cc_rhs = xi, cc_depth = d })  dimitris committed May 17, 2011 542  | isGivenOrSolved gw  simonpj@microsoft.com committed Nov 12, 2010 543  = return SPCantSolve  simonpj@microsoft.com committed Sep 13, 2010 544 545 546 547  | Just tv2 <- tcGetTyVar_maybe xi = do { tch1 <- isTouchableMetaTyVar tv1 ; tch2 <- isTouchableMetaTyVar tv2 ; case (tch1, tch2) of  dimitris committed Mar 28, 2012 548 549 550  (True, True) -> trySpontaneousEqTwoWay d gw tv1 tv2 (True, False) -> trySpontaneousEqOneWay d gw tv1 xi (False, True) -> trySpontaneousEqOneWay d gw tv2 (mkTyVarTy tv1)  simonpj@microsoft.com committed Nov 12, 2010 551  _ -> return SPCantSolve }  simonpj@microsoft.com committed Sep 13, 2010 552 553  | otherwise = do { tch1 <- isTouchableMetaTyVar tv1  dimitris committed Mar 28, 2012 554  ; if tch1 then trySpontaneousEqOneWay d gw tv1 xi  dimitris committed Nov 16, 2011 555 556  else do { traceTcS "Untouchable LHS, can't spontaneously solve workitem:"$ ppr workItem  simonpj@microsoft.com committed Nov 12, 2010 557  ; return SPCantSolve }  558  }  simonpj@microsoft.com committed Sep 13, 2010 559 560 561 562  -- No need for -- trySpontaneousSolve (CFunEqCan ...) = ... -- See Note [No touchables as FunEq RHS] in TcSMonad  simonpj@microsoft.com committed Nov 12, 2010 563 trySpontaneousSolve _ = return SPCantSolve  simonpj@microsoft.com committed Sep 13, 2010 564 565  ----------------  dimitris committed Nov 16, 2011 566 trySpontaneousEqOneWay :: SubGoalDepth  dimitris committed Mar 28, 2012 567  -> CtFlavor -> TcTyVar -> Xi -> TcS SPSolveResult  568 -- tv is a MetaTyVar, not untouchable  dimitris committed Mar 28, 2012 569 trySpontaneousEqOneWay d gw tv xi  dimitris committed Dec 22, 2011 570  | not (isSigTyVar tv) || isTyVarTy xi  dimitris committed Mar 28, 2012 571  = solveWithIdentity d gw tv xi  572  | otherwise -- Still can't solve, sig tyvar and non-variable rhs  simonpj@microsoft.com committed Nov 12, 2010 573  = return SPCantSolve  simonpj@microsoft.com committed Sep 13, 2010 574 575  ----------------  dimitris committed Nov 16, 2011 576 trySpontaneousEqTwoWay :: SubGoalDepth  dimitris committed Mar 28, 2012 577  -> CtFlavor -> TcTyVar -> TcTyVar -> TcS SPSolveResult  578 -- Both tyvars are *touchable* MetaTyvars so there is only a chance for kind error here  dimitris committed Nov 16, 2011 579   dimitris committed Mar 28, 2012 580 trySpontaneousEqTwoWay d gw tv1 tv2  Simon Peyton Jones committed Feb 17, 2012 581  = do { let k1_sub_k2 = k1 tcIsSubKind k2  dreixel committed Nov 11, 2011 582  ; if k1_sub_k2 && nicer_to_update_tv2  dimitris committed Mar 28, 2012 583 584  then solveWithIdentity d gw tv2 (mkTyVarTy tv1) else solveWithIdentity d gw tv1 (mkTyVarTy tv2) }  simonpj@microsoft.com committed Sep 13, 2010 585 586 587 588 589 590  where k1 = tyVarKind tv1 k2 = tyVarKind tv2 nicer_to_update_tv2 = isSigTyVar tv1 || isSystemName (Var.varName tv2) \end{code}  591 592 593 594 Note [Kind errors] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider the wanted problem: alpha ~ (# Int, Int #)  dreixel committed Nov 21, 2011 595 where alpha :: ArgKind and (# Int, Int #) :: (#). We can't spontaneously solve this constraint,  596 but we should rather reject the program that give rise to it. If 'trySpontaneousEqTwoWay'  simonpj@microsoft.com committed Nov 12, 2010 597 simply returns @CantSolve@ then that wanted constraint is going to propagate all the way and  598 get quantified over in inference mode. That's bad because we do know at this point that the  simonpj@microsoft.com committed Nov 12, 2010 599 constraint is insoluble. Instead, we call 'recKindErrorTcS' here, which will fail later on.  600 601  The same applies in canonicalization code in case of kind errors in the givens.  602   603 However, when we canonicalize givens we only check for compatibility (@compatKind@).  simonpj@microsoft.com committed Nov 12, 2010 604 If there were a kind error in the givens, this means some form of inconsistency or dead code.  605   simonpj@microsoft.com committed Nov 12, 2010 606 607 608 609 610 You may think that when we spontaneously solve wanteds we may have to look through the bindings to determine the right kind of the RHS type. E.g one may be worried that xi is @alpha@ where alpha :: ? and a previous spontaneous solving has set (alpha := f) with (f :: *). But we orient our constraints so that spontaneously solved ones can rewrite all other constraint so this situation can't happen.  611   612 613 Note [Spontaneous solving and kind compatibility] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  simonpj@microsoft.com committed Jan 12, 2011 614 615 616 Note that our canonical constraints insist that *all* equalities (tv ~ xi) or (F xis ~ rhs) require the LHS and the RHS to have *compatible* the same kinds. ("compatible" means one is a subKind of the other.)  617   simonpj@microsoft.com committed Jan 12, 2011 618 619 620 621 622 623 624 625 626 627 628 629 630 631  - It can't be *equal* kinds, because b) wanted constraints don't necessarily have identical kinds eg alpha::? ~ Int b) a solved wanted constraint becomes a given - SPJ thinks that *given* constraints (tv ~ tau) always have that tau has a sub-kind of tv; and when solving wanted constraints in trySpontaneousEqTwoWay we re-orient to achieve this. - Note that the kind invariant is maintained by rewriting. Eg wanted1 rewrites wanted2; if both were compatible kinds before, wanted2 will be afterwards. Similarly givens. Caveat:  632 633 634 635 636 637 638 639 640  - 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'  simonpj@microsoft.com committed Sep 13, 2010 641 642 643 644 645 646 647  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 648  given : a ~ alpha [having unified alpha := a]  simonpj@microsoft.com committed Sep 13, 2010 649 650 651 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 Nov 12, 2010 652 We avoid this problem by orienting the resulting given so that the unification  simonpj@microsoft.com committed Oct 07, 2010 653 654 variable is on the left. [Note that alternatively we could attempt to enforce this at canonicalization]  simonpj@microsoft.com committed Sep 13, 2010 655   simonpj@microsoft.com committed Oct 07, 2010 656 657 658 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 659 660 661  \begin{code} ----------------  simonpj@microsoft.com committed Nov 12, 2010 662   dimitris committed Nov 16, 2011 663 solveWithIdentity :: SubGoalDepth  dimitris committed Mar 28, 2012 664  -> CtFlavor -> TcTyVar -> Xi -> TcS SPSolveResult  simonpj@microsoft.com committed Sep 13, 2010 665 666 -- Solve with the identity coercion -- Precondition: kind(xi) is a sub-kind of kind(tv)  simonpj@microsoft.com committed Oct 07, 2010 667 668 669 -- Precondition: CtFlavor is Wanted or Derived -- See [New Wanted Superclass Work] to see why solveWithIdentity -- must work for Derived as well as Wanted  simonpj@microsoft.com committed Nov 12, 2010 670 -- Returns: workItem where  671 -- workItem = the new Given constraint  dimitris committed Mar 28, 2012 672 673 674 675 676 677 678 solveWithIdentity d wd tv xi = do { let tv_ty = mkTyVarTy tv ; traceTcS "Sneaky unification:" $vcat [text "Constraint:" <+> ppr wd, text "Coercion:" <+> pprEq tv_ty xi, text "Left Kind is:" <+> ppr (typeKind tv_ty), text "Right Kind is:" <+> ppr (typeKind xi) ]  679   Simon Peyton Jones committed Mar 02, 2012 680 681 682 683 684 685 686  ; let xi' = defaultKind xi -- We only instantiate kind unification variables -- with simple kinds like *, not OpenKind or ArgKind -- cf TcUnify.uUnboundKVar ; setWantedTyBind tv xi' ; let refl_xi = mkTcReflCo xi'  dimitris committed Nov 16, 2011 687   dimitris committed Mar 28, 2012 688 689  ; when (isWanted wd)$ setEvBind (flav_evar wd) (EvCoercion refl_xi)  simonpj@microsoft.com committed Nov 12, 2010 690   dimitris committed Mar 28, 2012 691 692 693 694 695 696 697  ; ev_given <- newGivenEvVar (mkTcEqPred tv_ty xi') (EvCoercion refl_xi) >>= (return . mn_thing) ; let given_fl = Given (mkGivenLoc (flav_wloc wd) UnkSkol) ev_given ; return $SPSolved (CTyEqCan { cc_flavor = given_fl , cc_tyvar = tv, cc_rhs = xi', cc_depth = d }) }  dimitris committed Nov 16, 2011 698 699 \end{code}  simonpj@microsoft.com committed Sep 13, 2010 700 701 702 703 704 705 706  ********************************************************************************* * * The interact-with-inert Stage * * *********************************************************************************  simonpj@microsoft.com committed Feb 21, 2011 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 Note [The Solver Invariant] ~~~~~~~~~~~~~~~~~~~~~~~~~~~ We always add Givens first. So you might think that the solver has the invariant If the work-item is Given, then the inert item must Given But this isn't quite true. Suppose we have, c1: [W] beta ~ [alpha], c2 : [W] blah, c3 :[W] alpha ~ Int After processing the first two, we get c1: [G] beta ~ [alpha], c2 : [W] blah Now, c3 does not interact with the the given c1, so when we spontaneously solve c3, we must re-react it with the inert set. So we can attempt a reaction between inert c2 [W] and work-item c3 [G]. It *is* true that [Solver Invariant] If the work-item is Given, AND there is a reaction then the inert item must Given or, equivalently, If the work-item is Given, and the inert item is Wanted/Derived then there is no reaction  simonpj@microsoft.com committed Sep 13, 2010 732 733 734 \begin{code} -- Interaction result of WorkItem <~> AtomicInert  dimitris committed Nov 16, 2011 735 736 737 738 data InteractResult = IRWorkItemConsumed { ir_fire :: String } | IRInertConsumed { ir_fire :: String } | IRKeepGoing { ir_fire :: String }  simonpj@microsoft.com committed Feb 21, 2011 739   dimitris committed Nov 16, 2011 740 741 irWorkItemConsumed :: String -> TcS InteractResult irWorkItemConsumed str = return (IRWorkItemConsumed str)  simonpj@microsoft.com committed Sep 13, 2010 742   dimitris committed Nov 16, 2011 743 744 irInertConsumed :: String -> TcS InteractResult irInertConsumed str = return (IRInertConsumed str)  simonpj@microsoft.com committed Sep 13, 2010 745   dimitris committed Nov 16, 2011 746 747 748 749 irKeepGoing :: String -> TcS InteractResult irKeepGoing str = return (IRKeepGoing str) -- You can't discard neither workitem or inert, but you must keep -- going. It's possible that new work is waiting in the TcS worklist.  750 751   dimitris committed Nov 16, 2011 752 753 754 755 interactWithInertsStage :: WorkItem -> TcS StopOrContinue -- Precondition: if the workitem is a CTyEqCan then it will not be able to -- react with anything at this stage. interactWithInertsStage wi  simonpj@microsoft.com committed Feb 21, 2011 756  = do { ctxt <- getTcSContext  dimitris committed Nov 16, 2011 757 758 759  ; if simplEqsOnly ctxt then return (ContinueWith wi) else  dimitris committed Mar 28, 2012 760 761 762 763  do { traceTcS "interactWithInerts"$ text "workitem = " <+> ppr wi ; rels <- extractRelevantInerts wi ; traceTcS "relevant inerts are:" $ppr rels ; foldlBagM interact_next (ContinueWith wi) rels } }  dimitris committed Nov 16, 2011 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789  where interact_next Stop atomic_inert = updInertSetTcS atomic_inert >> return Stop interact_next (ContinueWith wi) atomic_inert = do { ir <- doInteractWithInert atomic_inert wi ; let mk_msg rule keep_doc = text rule <+> keep_doc <+> vcat [ ptext (sLit "Inert =") <+> ppr atomic_inert , ptext (sLit "Work =") <+> ppr wi ] ; case ir of IRWorkItemConsumed { ir_fire = rule } -> do { bumpStepCountTcS ; traceFireTcS (cc_depth wi) (mk_msg rule (text "WorkItemConsumed")) ; updInertSetTcS atomic_inert ; return Stop } IRInertConsumed { ir_fire = rule } -> do { bumpStepCountTcS ; traceFireTcS (cc_depth atomic_inert) (mk_msg rule (text "InertItemConsumed")) ; return (ContinueWith wi) } IRKeepGoing {} -- Should we do a bumpStepCountTcS? No for now. -> do { updInertSetTcS atomic_inert ; return (ContinueWith wi) } }  simonpj@microsoft.com committed Sep 13, 2010 790 791 --------------------------------------------  dimitris committed Nov 16, 2011 792 793 doInteractWithInert :: Ct -> Ct -> TcS InteractResult -- Identical class constraints.  simonpj@microsoft.com committed Jan 12, 2011 794 doInteractWithInert  dimitris committed Mar 28, 2012 795 796  inertItem@(CDictCan { cc_flavor = fl1, cc_class = cls1, cc_tyargs = tys1 }) workItem@(CDictCan { cc_flavor = fl2, cc_class = cls2, cc_tyargs = tys2 })  simonpj@microsoft.com committed Sep 13, 2010 797   dimitris committed Jun 08, 2011 798  | cls1 == cls2  batterseapower committed Sep 06, 2011 799 800  = do { let pty1 = mkClassPred cls1 tys1 pty2 = mkClassPred cls2 tys2  simonpj@microsoft.com committed Nov 12, 2010 801  inert_pred_loc = (pty1, pprFlavorArising fl1)  simonpj@microsoft.com committed Feb 17, 2011 802  work_item_pred_loc = (pty2, pprFlavorArising fl2)  dimitris committed Jun 08, 2011 803   dimitris committed Nov 16, 2011 804 805 806  ; traceTcS "doInteractWithInert" (vcat [ text "inertItem = " <+> ppr inertItem , text "workItem = " <+> ppr workItem ])  dimitris committed Jun 08, 2011 807 808 809 810 811 812  ; any_fundeps <- if isGivenOrSolved fl1 && isGivenOrSolved fl2 then return Nothing -- NB: We don't create fds for given (and even solved), have not seen a useful -- situation for these and even if we did we'd have to be very careful to only -- create Derived's and not Wanteds.  dimitris committed Dec 15, 2011 813 814 815  else do { let fd_eqns = improveFromAnother inert_pred_loc work_item_pred_loc ; wloc <- get_workitem_wloc fl2 ; rewriteWithFunDeps fd_eqns tys2 wloc }  dimitris committed Jun 08, 2011 816 817 818 819 820  -- See Note [Efficient Orientation], [When improvement happens] ; case any_fundeps of -- No Functional Dependencies Nothing  dimitris committed Mar 28, 2012 821  | eqTypes tys1 tys2 -> solveOneFromTheOther "Cls/Cls" fl1 workItem  dimitris committed Nov 16, 2011 822  | otherwise -> irKeepGoing "NOP"  dimitris committed Jun 08, 2011 823 824  -- Actual Functional Dependencies  dimitris committed Nov 16, 2011 825 826  Just (_rewritten_tys2,_cos2,fd_work) -- Standard thing: create derived fds and keep on going. Importantly we don't  dimitris committed Jun 08, 2011 827  -- throw workitem back in the worklist because this can cause loops. See #5236.  dimitris committed Nov 16, 2011 828 829  -> do { emitFDWorkAsDerived fd_work (cc_depth workItem) ; irKeepGoing "Cls/Cls (new fundeps)" } -- Just keep going without droping the inert  dimitris committed Jun 08, 2011 830  }  dimitris committed Mar 28, 2012 831 832 833 834 835 836 837 838 839 840 841  where get_workitem_wloc (Wanted wl _) = return wl get_workitem_wloc (Derived wl _) = return wl get_workitem_wloc _ = pprPanic "Unexpected given workitem!"$ vcat [ text "Work item =" <+> ppr workItem , text "Inert item=" <+> ppr inertItem] -- Two pieces of irreducible evidence: if their types are *exactly identical* -- we can rewrite them. We can never improve using this: -- if we want ty1 :: Constraint and have ty2 :: Constraint it clearly does not -- mean that (ty1 ~ ty2) doInteractWithInert (CIrredEvCan { cc_flavor = ifl, cc_ty = ty1 })  batterseapower committed Sep 10, 2011 842 843  workItem@(CIrredEvCan { cc_ty = ty2 }) | ty1 eqType ty2  dimitris committed Mar 28, 2012 844  = solveOneFromTheOther "Irred/Irred" ifl workItem  batterseapower committed Sep 10, 2011 845   simonpj@microsoft.com committed Sep 13, 2010 846 847 848 849 850 -- 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.  dimitris committed Mar 28, 2012 851 doInteractWithInert (CIPCan { cc_flavor = ifl, cc_ip_nm = nm1, cc_ip_ty = ty1 })  simonpj@microsoft.com committed Sep 13, 2010 852  workItem@(CIPCan { cc_flavor = wfl, cc_ip_nm = nm2, cc_ip_ty = ty2 })  dimitris committed May 17, 2011 853  | nm1 == nm2 && isGivenOrSolved wfl && isGivenOrSolved ifl  simonpj@microsoft.com committed Sep 17, 2010 854 855 856  = -- See Note [Overriding implicit parameters] -- Dump the inert item, override totally with the new one -- Do not require type equality  simonpj@microsoft.com committed Feb 17, 2011 857 858  -- For example, given let ?x::Int = 3 in let ?x::Bool = True in ... -- we must *override* the outer one with the inner one  dimitris committed Nov 16, 2011 859  irInertConsumed "IP/IP (override inert)"  simonpj@microsoft.com committed Sep 17, 2010 860   861  | nm1 == nm2 && ty1 eqType ty2  dimitris committed Mar 28, 2012 862  = solveOneFromTheOther "IP/IP" ifl workItem  simonpj@microsoft.com committed Sep 13, 2010 863   simonpj@microsoft.com committed Sep 17, 2010 864  | nm1 == nm2  simonpj@microsoft.com committed Sep 13, 2010 865  = -- See Note [When improvement happens]  dimitris committed Mar 28, 2012 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911  do { mb_eqv <- newWantedEvVar (mkEqPred ty2 ty1) -- co :: ty2 ~ ty1, see Note [Efficient orientation] ; cv <- case mb_eqv of Fresh eqv -> do { updWorkListTcS $extendWorkListEq$ CNonCanonical { cc_flavor = Wanted new_wloc eqv , cc_depth = cc_depth workItem } ; return eqv } Cached eqv -> return eqv ; case wfl of Wanted {} -> let ip_co = mkTcTyConAppCo (ipTyCon nm1) [mkTcCoVarCo cv] in do { setEvBind (ctId "doInteractWithInert" workItem) $mkEvCast (flav_evar ifl) (mkTcSymCo ip_co) ; irWorkItemConsumed "IP/IP (solved by rewriting)" } _ -> pprPanic "Unexpected IP constraint" (ppr workItem) } where new_wloc | Wanted wl _ <- wfl = wl | Derived wl _ <- wfl = wl | Wanted wl _ <- ifl = wl | Derived wl _ <- ifl = wl | otherwise = panic "Solve IP: no WantedLoc!" {-- DELETEME ; when (isWanted wfl)$ do { setEvBind (flav_evar wfl) (mkEvCast (flav_evar ifl) ; mb_new_fl <- rewriteCtFlavor wfl (mkTyConApp (ipTyCon nm1) [ty1]) -- IP x ty1 (mkTcTyConAppCo (ipTyCon nm1) [mkTcCoVarCo cv]) -- IP x ty1 ~ IP x ty2 ; case mb_new_fl of Nothing -> pprPanic "Unexpected cached IP constraint!" empty Just new_fl -> irWorkItemConsumed "IP/IP (solved by rewriting)" } where new_wloc | Wanted wl _ <- wfl = wl | Derived wl _ <- wfl = wl | Wanted wl _ <- ifl = wl | Derived wl _ <- ifl = wl | otherwise = panic "Solve IP: no WantedLoc!" eqv <- newWantedEvVar (mkEqPred ty2 ty1) -- See Note [Efficient Orientation] ; let flav = Wanted (combineCtLoc ifl wfl)  dimitris committed Nov 16, 2011 912 913 914 915 916 917 918  ; eqv <- newEqVar flav ty2 ty1 -- See Note [Efficient Orientation] ; when (isNewEvVar eqv) $(let ct = CNonCanonical { cc_id = evc_the_evvar eqv , cc_flavor = flav , cc_depth = cc_depth workItem } in updWorkListTcS (extendWorkListEq ct))  U-EUROPE\dimitris committed Apr 27, 2011 919 920 921 922  ; case wfl of Given {} -> pprPanic "Unexpected given IP" (ppr workItem) Derived {} -> pprPanic "Unexpected derived IP" (ppr workItem) Wanted {} ->  dimitris committed Nov 28, 2011 923  do { _ <- setEvBind (cc_id workItem)  Simon Peyton Jones committed Dec 05, 2011 924  (mkEvCast id1 (mkTcSymCo (mkTcTyConAppCo (ipTyCon nm1) [mkTcCoVarCo (evc_the_evvar eqv)]))) wfl  dimitris committed Nov 16, 2011 925  ; irWorkItemConsumed "IP/IP (solved by rewriting)" } }  dimitris committed Mar 28, 2012 926 927 -}  simonpj@microsoft.com committed Sep 13, 2010 928   dimitris committed Mar 28, 2012 929 930 931 932 doInteractWithInert ii@(CFunEqCan { cc_flavor = fl1, cc_fun = tc1 , cc_tyargs = args1, cc_rhs = xi1, cc_depth = d1 }) wi@(CFunEqCan { cc_flavor = fl2, cc_fun = tc2 , cc_tyargs = args2, cc_rhs = xi2, cc_depth = d2 })  dimitris committed Nov 16, 2011 933  | lhss_match  dimitris committed Mar 28, 2012 934 935  , isSolved fl1 -- Inert is solved and we can simply ignore it -- when workitem is given/solved  dimitris committed Nov 16, 2011 936 937  , isGivenOrSolved fl2 = irInertConsumed "FunEq/FunEq"  dimitris committed Mar 28, 2012 938 939 940  | lhss_match , isSolved fl2 -- Workitem is solved and we can ignore it when -- the inert is given/solved  dimitris committed Nov 16, 2011 941 942  , isGivenOrSolved fl1 = irWorkItemConsumed "FunEq/FunEq"  943  | fl1 canSolve fl2 && lhss_match  dimitris committed Mar 28, 2012 944 945 946 947 948  = do { traceTcS "interact with inerts: FunEq/FunEq"$ vcat [ text "workitem =" <+> ppr wi , text "inertitem=" <+> ppr ii ] ; xCtFlavor fl2 [mkTcEqPred xi2 xi1] (xev co1) $what_next d2  dimitris committed Nov 16, 2011 949  ; irWorkItemConsumed "FunEq/FunEq" }  950  | fl2 canSolve fl1 && lhss_match  dimitris committed Mar 28, 2012 951  = do { xCtFlavor fl1 [mkTcEqPred xi1 xi2] (xev co2)$ what_next d1  dimitris committed Nov 16, 2011 952  ; irInertConsumed "FunEq/FunEq"}  simonpj@microsoft.com committed Sep 13, 2010 953  where  954  lhss_match = tc1 == tc2 && eqTypes args1 args2  dimitris committed Mar 28, 2012 955 956 957 958 959 960 961 962 963 964 965 966  what_next d [new_fl] = updWorkListTcS $extendWorkListEq (CNonCanonical {cc_flavor=new_fl,cc_depth = d}) what_next _ _ = return () co1 = mkTcCoVarCo$ flav_evar fl1 co2 = mkTcCoVarCo $flav_evar fl2 mk_sym_co x = mkTcSymCo (mkTcCoVarCo x) xev co = XEvTerm xcomp xdecomp where xdecomp x = [EvCoercion (mk_sym_co x mkTcTransCo co)] xcomp [x] = EvCoercion (co mkTcTransCo mk_sym_co x) xcomp _ = panic "No more goals!"  dimitris committed Nov 16, 2011 967 968 doInteractWithInert _ _ = irKeepGoing "NOP"  dimitris committed Mar 28, 2012 969 {- DELETE  dimitris committed Nov 16, 2011 970 rewriteEqLHS :: WhichComesFromInert -> (EqVar,Xi) -> (EqVar,SubGoalDepth,CtFlavor,Xi) -> TcS ()  971 -- Used to ineract two equalities of the following form:  simonpj@microsoft.com committed Sep 13, 2010 972 973 -- First Equality: co1: (XXX ~ xi1) -- Second Equality: cv2: (XXX ~ xi2)  simonpj@microsoft.com committed Feb 21, 2011 974 -- Where the cv1 canRewrite cv2 equality  975 976 -- We have an option of creating new work (xi1 ~ xi2) OR (xi2 ~ xi1), -- See Note [Efficient Orientation] for that  dimitris committed Nov 16, 2011 977 rewriteEqLHS LeftComesFromInert (eqv1,xi1) (eqv2,d,gw,xi2)  dimitris committed Nov 28, 2011 978  = do { delCachedEvVar eqv2 gw -- Similarly to canonicalization!  dimitris committed Nov 16, 2011 979 980  ; evc <- newEqVar gw xi2 xi1 ; let eqv2' = evc_the_evvar evc  dimitris committed Nov 28, 2011 981  ; gw' <- case gw of  dimitris committed Nov 16, 2011 982  Wanted {}  dimitris committed Nov 28, 2011 983  -> setEqBind eqv2  Simon Peyton Jones committed Dec 05, 2011 984  (mkTcCoVarCo eqv1 mkTcTransCo mkTcSymCo (mkTcCoVarCo eqv2')) gw  dimitris committed Nov 28, 2011 985 986  Given {} -> setEqBind eqv2'  Simon Peyton Jones committed Dec 05, 2011 987  (mkTcSymCo (mkTcCoVarCo eqv2) mkTcTransCo mkTcCoVarCo eqv1) gw  dimitris committed Nov 16, 2011 988  Derived {}  dimitris committed Nov 28, 2011 989  -> return gw  dimitris committed Nov 16, 2011 990 991  ; when (isNewEvVar evc)$ updWorkListTcS (extendWorkListEq (CNonCanonical { cc_id = eqv2'  dimitris committed Nov 28, 2011 992  , cc_flavor = gw'  dimitris committed Nov 16, 2011 993 994 995  , cc_depth = d } ) ) } rewriteEqLHS RightComesFromInert (eqv1,xi1) (eqv2,d,gw,xi2)  dimitris committed Nov 28, 2011 996  = do { delCachedEvVar eqv2 gw -- Similarly to canonicalization!  dimitris committed Nov 16, 2011 997 998  ; evc <- newEqVar gw xi1 xi2 ; let eqv2' = evc_the_evvar evc  dimitris committed Nov 28, 2011 999  ; gw' <- case gw of  dimitris committed Nov 16, 2011 1000  Wanted {}  dimitris committed Nov 28, 2011 1001  -> setEqBind eqv2  Simon Peyton Jones committed Dec 05, 2011 1002  (mkTcCoVarCo eqv1 mkTcTransCo mkTcCoVarCo eqv2') gw  dimitris committed Nov 16, 2011 1003  Given {}  dimitris committed Nov 28, 2011 1004  -> setEqBind eqv2'  Simon Peyton Jones committed Dec 05, 2011 1005  (mkTcSymCo (mkTcCoVarCo eqv1) mkTcTransCo mkTcCoVarCo eqv2) gw  dimitris committed Nov 16, 2011 1006  Derived {}  dimitris committed Nov 28, 2011 1007  -> return gw  dimitris committed Nov 16, 2011 1008 1009 1010  ; when (isNewEvVar evc) $updWorkListTcS (extendWorkListEq (CNonCanonical { cc_id = eqv2'  dimitris committed Nov 28, 2011 1011  , cc_flavor = gw'  dimitris committed Nov 16, 2011 1012 1013  , cc_depth = d } ) ) }  dimitris committed Mar 28, 2012 1014 1015 1016 1017 1018 -} solveOneFromTheOther :: String -- Info -> CtFlavor -- Inert  dimitris committed Nov 16, 2011 1019 1020 1021 1022 1023  -> Ct -- WorkItem -> TcS InteractResult -- Preconditions: -- 1) inert and work item represent evidence for the /same/ predicate -- 2) ip/class/irred evidence (no coercions) only  dimitris committed Mar 28, 2012 1024 solveOneFromTheOther info ifl workItem  simonpj@microsoft.com committed Feb 17, 2011 1025  | isDerived wfl  dimitris committed Nov 16, 2011 1026  = irWorkItemConsumed ("Solved[DW] " ++ info)  simonpj@microsoft.com committed Feb 17, 2011 1027   simonpj@microsoft.com committed Feb 21, 2011 1028 1029 1030  | isDerived ifl -- The inert item is Derived, we can just throw it away, -- The workItem is inert wrt earlier inert-set items, -- so it's safe to continue on from this point  dimitris committed Nov 16, 2011 1031  = irInertConsumed ("Solved[DI] " ++ info)  simonpj@microsoft.com committed Jan 12, 2011 1032   dimitris committed Mar 28, 2012 1033  | isSolved ifl, isGivenOrSolved wfl  dimitris committed May 17, 2011 1034  -- Same if the inert is a GivenSolved -- just get rid of it  dimitris committed Nov 16, 2011 1035  = irInertConsumed ("Solved[SI] " ++ info)  dimitris committed May 17, 2011 1036   simonpj@microsoft.com committed Feb 21, 2011 1037 1038 1039  | otherwise = ASSERT( ifl canSolve wfl ) -- Because of Note [The Solver Invariant], plus Derived dealt with  dimitris committed Mar 28, 2012 1040  do { when (isWanted wfl)$ setEvBind wid (EvId iid)  simonpj@microsoft.com committed Feb 21, 2011 1041 1042  -- Overwrite the binding, if one exists -- If both are Given, we already have evidence; no need to duplicate  dimitris committed Nov 16, 2011 1043  ; irWorkItemConsumed ("Solved " ++ info) }  simonpj@microsoft.com committed Sep 13, 2010 1044 1045  where wfl = cc_flavor workItem  dimitris committed Mar 28, 2012 1046 1047  wid = ctId "solveOneFromtheOther" workItem iid = flav_evar ifl  dimitris committed Jun 08, 2011 1048   simonpj@microsoft.com committed Sep 13, 2010 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 \end{code} Note [Superclasses and recursive dictionaries] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Overlaps with Note [SUPERCLASS-LOOP 1] Note [SUPERCLASS-LOOP 2] Note [Recursive instances and superclases] ToDo: check overlap and delete redundant stuff Right before adding a given into the inert set, we must produce some more work, that will bring the superclasses of the given into scope. The superclass constraints go into our worklist. When we simplify a wanted constraint, if we first see a matching instance, we may produce new wanted work. To (1) avoid doing this work twice in the future and (2) to handle recursive dictionaries we may cache''  simonpj@microsoft.com committed Jan 12, 2011 1066 1067 1068 this item as given into our inert set WITHOUT adding its superclass constraints, otherwise we'd be in danger of creating a loop [In fact this was the exact reason for doing the isGoodRecEv check in an older version of the type checker].  simonpj@microsoft.com committed Sep 13, 2010 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078  But now we have added partially solved constraints to the worklist which may interact with other wanteds. Consider the example: Example 1: class Eq b => Foo a b --- 0-th selector instance Eq a => Foo [a] a --- fooDFun and wanted (Foo [t] t). We are first going to see that the instance matches  simonpj@microsoft.com committed Jan 12, 2011 1079 and create an inert set that includes the solved (Foo [t] t) but not its superclasses:  simonpj@microsoft.com committed Sep 13, 2010 1080 1081 1082 1083  d1 :_g Foo [t] t d1 := EvDFunApp fooDFun d3 Our work list is going to contain a new *wanted* goal d3 :_w Eq t  simonpj@microsoft.com committed Jan 12, 2011 1084 Ok, so how do we get recursive dictionaries, at all:  simonpj@microsoft.com committed Sep 13, 2010 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252 1253 1254 1255 1256 1257 1258 1259 1260 1261 1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294 1295 1296 1297 1298 1299 1300 1301 1302 1303 1304 1305 1306 1307 1308 1309 1310 1311 1312 1313 1314 1315 1316 1317 1318 1319 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 1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 1380 1381 1382 1383 1384 1385 1386 1387 1388 1389 1390 1391  Example 2: data D r = ZeroD | SuccD (r (D r)); instance (Eq (r (D r))) => Eq (D r) where ZeroD == ZeroD = True (SuccD a) == (SuccD b) = a == b _ == _ = False; equalDC :: D [] -> D [] -> Bool; equalDC = (==); We need to prove (Eq (D [])). Here's how we go: d1 :_w Eq (D []) by instance decl, holds if d2 :_w Eq [D []] where d1 = dfEqD d2 *BUT* we have an inert set which gives us (no superclasses): d1 :_g Eq (D []) By the instance declaration of Eq we can show the 'd2' goal if d3 :_w Eq (D []) where d2 = dfEqList d3 d1 = dfEqD d2 Now, however this wanted can interact with our inert d1 to set: d3 := d1 and solve the goal. Why was this interaction OK? Because, if we chase the evidence of d1 ~~> dfEqD d2 ~~-> dfEqList d3, so by setting d3 := d1 we are really setting d3 := dfEqD2 (dfEqList d3) which is FINE because the use of d3 is protected by the instance function applications. So, our strategy is to try to put solved wanted dictionaries into the inert set along with their superclasses (when this is meaningful, i.e. when new wanted goals are generated) but solve a wanted dictionary from a given only in the case where the evidence variable of the wanted is mentioned in the evidence of the given (recursively through the evidence binds) in a protected way: more instance function applications than superclass selectors. Here are some more examples from GHC's previous type checker Example 3: This code arises in the context of "Scrap Your Boilerplate with Class" class Sat a class Data ctx a instance Sat (ctx Char) => Data ctx Char -- dfunData1 instance (Sat (ctx [a]), Data ctx a) => Data ctx [a] -- dfunData2 class Data Maybe a => Foo a instance Foo t => Sat (Maybe t) -- dfunSat instance Data Maybe a => Foo a -- dfunFoo1 instance Foo a => Foo [a] -- dfunFoo2 instance Foo [Char] -- dfunFoo3 Consider generating the superclasses of the instance declaration instance Foo a => Foo [a] So our problem is this d0 :_g Foo t d1 :_w Data Maybe [t] We may add the given in the inert set, along with its superclasses [assuming we don't fail because there is a matching instance, see tryTopReact, given case ] Inert: d0 :_g Foo t WorkList d01 :_g Data Maybe t -- d2 := EvDictSuperClass d0 0 d1 :_w Data Maybe [t] Then d2 can readily enter the inert, and we also do solving of the wanted Inert: d0 :_g Foo t d1 :_s Data Maybe [t] d1 := dfunData2 d2 d3 WorkList d2 :_w Sat (Maybe [t]) d3 :_w Data Maybe t d01 :_g Data Maybe t Now, we may simplify d2 more: Inert: d0 :_g Foo t d1 :_s Data Maybe [t] d1 := dfunData2 d2 d3 d1 :_g Data Maybe [t] d2 :_g Sat (Maybe [t]) d2 := dfunSat d4 WorkList: d3 :_w Data Maybe t d4 :_w Foo [t] d01 :_g Data Maybe t Now, we can just solve d3. Inert d0 :_g Foo t d1 :_s Data Maybe [t] d1 := dfunData2 d2 d3 d2 :_g Sat (Maybe [t]) d2 := dfunSat d4 WorkList d4 :_w Foo [t] d01 :_g Data Maybe t And now we can simplify d4 again, but since it has superclasses we *add* them to the worklist: Inert d0 :_g Foo t d1 :_s Data Maybe [t] d1 := dfunData2 d2 d3 d2 :_g Sat (Maybe [t]) d2 := dfunSat d4 d4 :_g Foo [t] d4 := dfunFoo2 d5 WorkList: d5 :_w Foo t d6 :_g Data Maybe [t] d6 := EvDictSuperClass d4 0 d01 :_g Data Maybe t Now, d5 can be solved! (and its superclass enter scope) Inert d0 :_g Foo t d1 :_s Data Maybe [t] d1 := dfunData2 d2 d3 d2 :_g Sat (Maybe [t]) d2 := dfunSat d4 d4 :_g Foo [t] d4 := dfunFoo2 d5 d5 :_g Foo t d5 := dfunFoo1 d7 WorkList: d7 :_w Data Maybe t d6 :_g Data Maybe [t] d8 :_g Data Maybe t d8 := EvDictSuperClass d5 0 d01 :_g Data Maybe t Now, two problems: [1] Suppose we pick d8 and we react him with d01. Which of the two givens should we keep? Well, we *MUST NOT* drop d01 because d8 contains recursive evidence that must not be used (look at case interactInert where both inert and workitem are givens). So we have several options: - Drop the workitem always (this will drop d8) This feels very unsafe -- what if the work item was the "good" one that should be used later to solve another wanted? - Don't drop anyone: the inert set may contain multiple givens! [This is currently implemented] The "don't drop anyone" seems the most safe thing to do, so now we come to problem 2: [2] We have added both d6 and d01 in the inert set, and we are interacting ou