TcInteract.lhs 81.2 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 import VarEnv import qualified Data.Traversable as Traversable  55 import Data.Maybe ( isJust )  dimitris committed Nov 28, 2011 56   dimitris committed Mar 29, 2012 57 import Control.Monad( when, unless )  dimitris committed Apr 02, 2012 58 import Pair ()  Simon Peyton Jones committed Jul 29, 2011 59 import UniqFM  simonpj@microsoft.com committed Sep 13, 2010 60 61 62 import FastString ( sLit ) import DynFlags \end{code}  dimitris committed Nov 16, 2011 63 64 ********************************************************************** * *  simonpj@microsoft.com committed Sep 13, 2010 65 66 67 68 * Main Interaction Solver * * * **********************************************************************  dimitris committed Nov 16, 2011 69 70 Note [Basic Simplifier Plan] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~  71   dimitris committed Nov 16, 2011 72 73 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 74   dimitris committed Nov 16, 2011 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 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 92 93 \begin{code}  dimitris committed Nov 16, 2011 94 95 solveInteractCts :: [Ct] -> TcS () solveInteractCts cts  dimitris committed Mar 28, 2012 96 97 98  = do { traceTcS "solveInteractCtS" (vcat [ text "cts =" <+> ppr cts ]) ; updWorkListTcS (appendWorkListCt cts) >> solveInteract }  dimitris committed Nov 16, 2011 99 100 101 solveInteractGiven :: GivenLoc -> [EvVar] -> TcS () solveInteractGiven gloc evs = solveInteractCts (map mk_noncan evs)  dimitris committed Mar 28, 2012 102  where mk_noncan ev = CNonCanonical { cc_flavor = Given gloc ev  dimitris committed Nov 16, 2011 103 104 105 106 107 108 109  , 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 110 111  = {-# SCC "solveInteract" #-} do { dyn_flags <- getDynFlags  dimitris committed Nov 16, 2011 112 113  ; let max_depth = ctxtStkDepth dyn_flags solve_loop  dimitris committed Nov 28, 2011 114 115  = {-# SCC "solve_loop" #-} do { sel <- selectNextWorkItem max_depth  dimitris committed Nov 16, 2011 116 117 118 119  ; case sel of NoWorkRemaining -- Done, successfuly (modulo frozen) -> return () MaxDepthExceeded ct -- Failure, depth exceeded  Simon Peyton Jones committed Jan 12, 2012 120  -> wrapErrTcS $solverDepthErrorTcS (cc_depth ct) [ct]  dimitris committed Nov 16, 2011 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140  NextWorkItem ct -- More work, loop around! -> runSolverPipeline thePipeline ct >> solve_loop } ; solve_loop } type WorkItem = Ct type SimplifierStage = WorkItem -> TcS StopOrContinue continueWith :: WorkItem -> TcS StopOrContinue continueWith work_item = return (ContinueWith work_item) data SelectWorkItem = NoWorkRemaining -- No more work left (effectively we're done!) | MaxDepthExceeded Ct -- More work left to do but this constraint has exceeded -- the max subgoal depth and we must stop | NextWorkItem Ct -- More work left, here's the next item to look at selectNextWorkItem :: SubGoalDepth -- Max depth allowed -> TcS SelectWorkItem selectNextWorkItem max_depth = updWorkListTcS_return pick_next  simonpj@microsoft.com committed Sep 13, 2010 141  where  dimitris committed Nov 16, 2011 142  pick_next :: WorkList -> (SelectWorkItem, WorkList)  dimitris committed Nov 28, 2011 143 144 145 146 147 148 149 150  pick_next wl = case selectWorkItem wl of (Nothing,_) -> (NoWorkRemaining,wl) -- No more work (Just ct, new_wl) | cc_depth ct > max_depth -- Depth exceeded -> (MaxDepthExceeded ct,new_wl) (Just ct, new_wl) -> (NextWorkItem ct, new_wl) -- New workitem and worklist  dimitris committed Nov 16, 2011 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183  runSolverPipeline :: [(String,SimplifierStage)] -- The pipeline -> WorkItem -- The work item -> TcS () -- Run this item down the pipeline, leaving behind new work and inerts runSolverPipeline pipeline workItem = do { initial_is <- getTcSInerts ; traceTcS "Start solver pipeline {"$ 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 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 \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 210 211 212 213 214 thePipeline :: [(String,SimplifierStage)] thePipeline = [ ("canonicalization", canonicalizationStage) , ("spontaneous solve", spontaneousSolveStage) , ("interact with inerts", interactWithInertsStage) , ("top-level reactions", topReactionsStage) ]  dimitris@microsoft.com committed Dec 09, 2010 215 216 217 218 \end{code} \begin{code}  simonpj@microsoft.com committed Sep 13, 2010 219   dimitris committed Mar 28, 2012 220   dimitris committed Nov 16, 2011 221 222 223 224 -- The canonicalization stage, see TcCanonical for details ---------------------------------------------------------- canonicalizationStage :: SimplifierStage canonicalizationStage = TcCanonical.canonicalize  simonpj@microsoft.com committed Oct 20, 2010 225   simonpj@microsoft.com committed Sep 13, 2010 226 227 228 229 230 231 232 233 \end{code} ********************************************************************************* * * The spontaneous-solve Stage * * *********************************************************************************  234 235 236 237 238 239 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 240 Case 1: In Rewriting Equalities (function rewriteEqLHS)  241   242 243 244 245 246 247 248 249 250  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.  simonpj@microsoft.com committed Nov 12, 2010 251 252 253 254 255 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.  256   simonpj@microsoft.com committed Sep 13, 2010 257 258 \begin{code} spontaneousSolveStage :: SimplifierStage  dimitris committed Nov 16, 2011 259 spontaneousSolveStage workItem  simonpj@microsoft.com committed Nov 12, 2010 260  = do { mSolve <- trySpontaneousSolve workItem  dimitris committed Nov 16, 2011 261  ; spont_solve mSolve }  dimitris committed Nov 28, 2011 262 263 264 265 266 267 268  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 269 270 271 272  = do { bumpStepCountTcS ; traceFireTcS (cc_depth workItem)$ ptext (sLit "Spontaneous") <+> parens (ppr (cc_flavor workItem)) <+> ppr workItem  dimitris committed Nov 28, 2011 273 274 275 276  -- NB: will add the item in the inerts ; kickOutRewritableInerts workItem' -- .. and Stop  dimitris committed Nov 16, 2011 277 278 279 280  ; return Stop } kickOutRewritableInerts :: Ct -> TcS () -- Pre: ct is a CTyEqCan  dimitris committed Nov 28, 2011 281 282 283 -- 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 284 kickOutRewritableInerts ct  dimitris committed Nov 28, 2011 285  = {-# SCC "kickOutRewritableInerts" #-}  dimitris committed Mar 28, 2012 286 287  do { traceTcS "kickOutRewritableInerts" $text "workitem = " <+> ppr ct ; (wl,ieqs) <- {-# SCC "kick_out_rewritable" #-}  dimitris committed Nov 28, 2011 288  modifyInertTcS (kick_out_rewritable ct)  dimitris committed Mar 28, 2012 289 290 291  ; traceTcS "Kicked out the following constraints"$ ppr wl ; is <- getTcSInerts ; traceTcS "Remaining inerts are" $ppr is  dimitris committed Nov 28, 2011 292   dimitris committed Mar 28, 2012 293 294 295 296 297  -- Step 1: Rewrite as many of the inert_eqs on the spot! -- NB: if it is a given constraint just use the cached evidence -- to optimize e.g. mkRefl coercions from spontaneously solved cts. ; bnds <- getTcEvBindsMap ; let ct_coercion = getCtCoercion bnds ct  dimitris committed Nov 28, 2011 298 299  ; new_ieqs <- {-# SCC "rewriteInertEqsFromInertEq" #-}  dimitris committed Mar 28, 2012 300 301 302 303 304 305 306 307 308 309 310  rewriteInertEqsFromInertEq (cc_tyvar ct, ct_coercion,cc_flavor ct) ieqs ; let upd_eqs is = is { inert_cans = new_ics } where ics = inert_cans is new_ics = ics { inert_eqs = new_ieqs } ; modifyInertTcS (\is -> ((), upd_eqs is)) ; is <- getTcSInerts ; traceTcS "Final inerts are"$ ppr is -- Step 2: Add the new guy in  dimitris committed Nov 28, 2011 311  ; updInertSetTcS ct  dimitris committed Nov 16, 2011 312 313 314  ; traceTcS "Kick out" (ppr ct  ppr wl) ; updWorkListTcS (unionWorkList wl) }  dimitris committed Nov 28, 2011 315   Simon Peyton Jones committed Dec 05, 2011 316 rewriteInertEqsFromInertEq :: (TcTyVar, TcCoercion, CtFlavor) -- A new substitution  dimitris committed Mar 28, 2012 317 318  -> TyVarEnv Ct -- All the inert equalities -> TcS (TyVarEnv Ct) -- The new inert equalities  dimitris committed Apr 02, 2012 319 320 321 322 rewriteInertEqsFromInertEq (subst_tv, _subst_co, subst_fl) ieqs -- The goal: traverse the inert equalities and throw some of them back to the worklist -- if you have to rewrite and recheck them for occurs check errors. -- This is delicate, see Note [Delicate equality kick-out]  dimitris committed Nov 28, 2011 323 324 325  = do { mieqs <- Traversable.mapM do_one ieqs ; traceTcS "Original inert equalities:" (ppr ieqs) ; let flatten_justs elem venv  dimitris committed Mar 28, 2012 326  | Just act <- elem = extendVarEnv venv (cc_tyvar act) act  dimitris committed Nov 28, 2011 327 328 329 330  | otherwise = venv final_ieqs = foldVarEnv flatten_justs emptyVarEnv mieqs ; traceTcS "Remaining inert equalities:" (ppr final_ieqs) ; return final_ieqs }  dimitris committed Nov 28, 2011 331   dimitris committed Mar 28, 2012 332  where do_one ct  dimitris committed Nov 28, 2011 333  | subst_fl canRewrite fl && (subst_tv elemVarSet tyVarsOfCt ct)  dimitris committed Mar 28, 2012 334  = if fl canRewrite subst_fl then  dimitris committed Apr 02, 2012 335 336 337 338 339  -- If also the inert can rewrite the subst then there is no danger of -- occurs check errors sor keep it there. No need to rewrite the inert equality -- (as we did in the past): See Note [Non-idempotent inert substitution] return (Just ct) -- used to be: rewrite_on_the_spot ct >>= ( return . Just )  dimitris committed Nov 28, 2011 340  else -- We have to throw inert back to worklist for occurs checks  dimitris committed Apr 02, 2012 341  updWorkListTcS (extendWorkListEq ct) >> return Nothing  dimitris committed Nov 28, 2011 342  | otherwise -- Just keep it there  dimitris committed Apr 02, 2012 343  = return (Just ct)  dimitris committed Nov 28, 2011 344  where  dimitris committed Mar 28, 2012 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360  fl = cc_flavor ct 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 361  where  dimitris committed Mar 30, 2012 362 363  rest_out = fro_out andCts dicts_out andCts ips_out andCts irs_out  dimitris committed Nov 28, 2011 364  kicked_out = WorkList { wl_eqs = []  dimitris committed Nov 28, 2011 365  , wl_funeqs = bagToList feqs_out  dimitris committed Mar 30, 2012 366  , wl_rest = bagToList rest_out }  dimitris committed Nov 16, 2011 367   dimitris committed Mar 28, 2012 368 369 370 371 372 373 374 375 376 377 378 379  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 380 381  fl = cc_flavor ct tv = cc_tyvar ct  dimitris committed Nov 28, 2011 382 383  (ips_out, ips_in) = partitionCCanMap rewritable ipmap  dimitris committed Nov 16, 2011 384   dimitris committed Mar 28, 2012 385  (feqs_out, feqs_in) = partCtFamHeadMap rewritable funeqmap  dimitris committed Nov 28, 2011 386  (dicts_out, dicts_in) = partitionCCanMap rewritable dictmap  dimitris committed Nov 16, 2011 387 388 389  (irs_out, irs_in) = partitionBag rewritable irreds (fro_out, fro_in) = partitionBag rewritable frozen  dimitris committed Nov 28, 2011 390 391  rewritable ct = (fl canRewrite cc_flavor ct) &&  dimitris committed Dec 22, 2011 392 393 394 395 396 397 398 399 400 401  (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 402 \end{code}  dimitris committed Nov 16, 2011 403   dimitris committed Nov 28, 2011 404 405 Note [Delicate equality kick-out] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  dimitris committed Nov 28, 2011 406   dimitris committed Nov 28, 2011 407 408 409 Delicate: When kicking out rewritable constraints, it would be safe to simply kick out all rewritable equalities, but instead we only kick out those  dimitris committed Apr 02, 2012 410 that, when rewritten, may result in occur-check errors. Example:  dimitris committed Nov 16, 2011 411   dimitris committed Apr 02, 2012 412  WorkItem = [G] a ~ b  dimitris committed Nov 28, 2011 413 414  Inerts = { [W] b ~ [a] } Now at this point the work item cannot be further rewritten by the  dimitris committed Apr 02, 2012 415 416 417 418 419 420 inert (due to the weaker inert flavor). Instead the workitem can rewrite the inert leading to potential occur check errors. So we must kick the inert out. On the other hand, if the inert flavor was 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).  dimitris committed Nov 28, 2011 421 422  The coclusion is: we kick out the 'dangerous' equalities that may  dimitris committed Apr 02, 2012 423 424 require recanonicalization (occurs checks) and the rest we keep there in the inerts without further checks.  dimitris committed Nov 28, 2011 425   dimitris committed Apr 02, 2012 426 427 In the past we used to rewrite-on-the-spot those equalities that we keep in, but this is no longer necessary see Note [Non-idempotent inert substitution].  dimitris committed Nov 28, 2011 428 429  \begin{code}  dimitris committed Nov 16, 2011 430 431 data SPSolveResult = SPCantSolve | SPSolved WorkItem  dimitris@microsoft.com committed Oct 06, 2010 432   simonpj@microsoft.com committed Nov 12, 2010 433 434 435 -- 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 436 -- @trySpontaneousSolve wi@ solves equalities where one side is a  simonpj@microsoft.com committed Nov 12, 2010 437 -- touchable unification variable.  simonpj@microsoft.com committed Sep 13, 2010 438 -- See Note [Touchables and givens]  simonpj@microsoft.com committed Nov 12, 2010 439 trySpontaneousSolve :: WorkItem -> TcS SPSolveResult  dimitris committed Mar 28, 2012 440 trySpontaneousSolve workItem@(CTyEqCan { cc_flavor = gw  dimitris committed Nov 16, 2011 441  , cc_tyvar = tv1, cc_rhs = xi, cc_depth = d })  dimitris committed May 17, 2011 442  | isGivenOrSolved gw  simonpj@microsoft.com committed Nov 12, 2010 443  = return SPCantSolve  simonpj@microsoft.com committed Sep 13, 2010 444 445 446 447  | Just tv2 <- tcGetTyVar_maybe xi = do { tch1 <- isTouchableMetaTyVar tv1 ; tch2 <- isTouchableMetaTyVar tv2 ; case (tch1, tch2) of  dimitris committed Mar 28, 2012 448 449 450  (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 451  _ -> return SPCantSolve }  simonpj@microsoft.com committed Sep 13, 2010 452 453  | otherwise = do { tch1 <- isTouchableMetaTyVar tv1  dimitris committed Mar 28, 2012 454  ; if tch1 then trySpontaneousEqOneWay d gw tv1 xi  dimitris committed Nov 16, 2011 455 456  else do { traceTcS "Untouchable LHS, can't spontaneously solve workitem:" $ppr workItem  simonpj@microsoft.com committed Nov 12, 2010 457  ; return SPCantSolve }  458  }  simonpj@microsoft.com committed Sep 13, 2010 459 460 461 462  -- No need for -- trySpontaneousSolve (CFunEqCan ...) = ... -- See Note [No touchables as FunEq RHS] in TcSMonad  simonpj@microsoft.com committed Nov 12, 2010 463 trySpontaneousSolve _ = return SPCantSolve  simonpj@microsoft.com committed Sep 13, 2010 464 465  ----------------  dimitris committed Nov 16, 2011 466 trySpontaneousEqOneWay :: SubGoalDepth  dimitris committed Mar 28, 2012 467  -> CtFlavor -> TcTyVar -> Xi -> TcS SPSolveResult  468 -- tv is a MetaTyVar, not untouchable  dimitris committed Mar 28, 2012 469 trySpontaneousEqOneWay d gw tv xi  dimitris committed Dec 22, 2011 470  | not (isSigTyVar tv) || isTyVarTy xi  dimitris committed Mar 28, 2012 471  = solveWithIdentity d gw tv xi  472  | otherwise -- Still can't solve, sig tyvar and non-variable rhs  simonpj@microsoft.com committed Nov 12, 2010 473  = return SPCantSolve  simonpj@microsoft.com committed Sep 13, 2010 474 475  ----------------  dimitris committed Nov 16, 2011 476 trySpontaneousEqTwoWay :: SubGoalDepth  dimitris committed Mar 28, 2012 477  -> CtFlavor -> TcTyVar -> TcTyVar -> TcS SPSolveResult  478 -- Both tyvars are *touchable* MetaTyvars so there is only a chance for kind error here  dimitris committed Nov 16, 2011 479   dimitris committed Mar 28, 2012 480 trySpontaneousEqTwoWay d gw tv1 tv2  Simon Peyton Jones committed Feb 17, 2012 481  = do { let k1_sub_k2 = k1 tcIsSubKind k2  dreixel committed Nov 11, 2011 482  ; if k1_sub_k2 && nicer_to_update_tv2  dimitris committed Mar 28, 2012 483 484  then solveWithIdentity d gw tv2 (mkTyVarTy tv1) else solveWithIdentity d gw tv1 (mkTyVarTy tv2) }  simonpj@microsoft.com committed Sep 13, 2010 485 486 487 488 489 490  where k1 = tyVarKind tv1 k2 = tyVarKind tv2 nicer_to_update_tv2 = isSigTyVar tv1 || isSystemName (Var.varName tv2) \end{code}  491 492 493 494 Note [Kind errors] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider the wanted problem: alpha ~ (# Int, Int #)  dreixel committed Nov 21, 2011 495 where alpha :: ArgKind and (# Int, Int #) :: (#). We can't spontaneously solve this constraint,  496 but we should rather reject the program that give rise to it. If 'trySpontaneousEqTwoWay'  simonpj@microsoft.com committed Nov 12, 2010 497 simply returns @CantSolve@ then that wanted constraint is going to propagate all the way and  498 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 499 constraint is insoluble. Instead, we call 'recKindErrorTcS' here, which will fail later on.  500 501  The same applies in canonicalization code in case of kind errors in the givens.  502   503 However, when we canonicalize givens we only check for compatibility (@compatKind@).  simonpj@microsoft.com committed Nov 12, 2010 504 If there were a kind error in the givens, this means some form of inconsistency or dead code.  505   simonpj@microsoft.com committed Nov 12, 2010 506 507 508 509 510 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.  511   512 513 Note [Spontaneous solving and kind compatibility] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  simonpj@microsoft.com committed Jan 12, 2011 514 515 516 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.)  517   simonpj@microsoft.com committed Jan 12, 2011 518 519 520 521 522 523 524 525 526 527 528 529 530 531  - 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:  532 533 534 535 536 537 538 539 540  - 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 541 542 543 544 545 546 547  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 548  given : a ~ alpha [having unified alpha := a]  simonpj@microsoft.com committed Sep 13, 2010 549 550 551 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 552 We avoid this problem by orienting the resulting given so that the unification  simonpj@microsoft.com committed Oct 07, 2010 553 554 variable is on the left. [Note that alternatively we could attempt to enforce this at canonicalization]  simonpj@microsoft.com committed Sep 13, 2010 555   simonpj@microsoft.com committed Oct 07, 2010 556 557 558 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 559 560 561  \begin{code} ----------------  simonpj@microsoft.com committed Nov 12, 2010 562   dimitris committed Nov 16, 2011 563 solveWithIdentity :: SubGoalDepth  dimitris committed Mar 28, 2012 564  -> CtFlavor -> TcTyVar -> Xi -> TcS SPSolveResult  simonpj@microsoft.com committed Sep 13, 2010 565 566 -- Solve with the identity coercion -- Precondition: kind(xi) is a sub-kind of kind(tv)  simonpj@microsoft.com committed Oct 07, 2010 567 568 569 -- 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 570 -- Returns: workItem where  571 -- workItem = the new Given constraint  dimitris committed Mar 28, 2012 572 573 574 575 576 577 578 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) ]  579   Simon Peyton Jones committed Mar 02, 2012 580 581 582 583 584 585 586  ; 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 587   dimitris committed Mar 28, 2012 588 589  ; when (isWanted wd) $setEvBind (flav_evar wd) (EvCoercion refl_xi)  simonpj@microsoft.com committed Nov 12, 2010 590   dimitris committed Mar 28, 2012 591 592 593 594 595 596 597  ; ev_given <- newGivenEvVar (mkTcEqPred tv_ty xi') (EvCoercion refl_xi) >>= (return . mn_thing) ; let given_fl = Given (mkGivenLoc (flav_wloc wd) UnkSkol) ev_given ; return$ SPSolved (CTyEqCan { cc_flavor = given_fl , cc_tyvar = tv, cc_rhs = xi', cc_depth = d }) }  dimitris committed Nov 16, 2011 598 599 \end{code}  simonpj@microsoft.com committed Sep 13, 2010 600 601 602 603 604 605 606  ********************************************************************************* * * The interact-with-inert Stage * * *********************************************************************************  simonpj@microsoft.com committed Feb 21, 2011 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 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 632 633 634 \begin{code} -- Interaction result of WorkItem <~> AtomicInert  dimitris committed Nov 16, 2011 635 636 637 638 data InteractResult = IRWorkItemConsumed { ir_fire :: String } | IRInertConsumed { ir_fire :: String } | IRKeepGoing { ir_fire :: String }  simonpj@microsoft.com committed Feb 21, 2011 639   dimitris committed Nov 16, 2011 640 641 irWorkItemConsumed :: String -> TcS InteractResult irWorkItemConsumed str = return (IRWorkItemConsumed str)  simonpj@microsoft.com committed Sep 13, 2010 642   dimitris committed Nov 16, 2011 643 644 irInertConsumed :: String -> TcS InteractResult irInertConsumed str = return (IRInertConsumed str)  simonpj@microsoft.com committed Sep 13, 2010 645   dimitris committed Nov 16, 2011 646 647 648 649 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.  650 651   dimitris committed Nov 16, 2011 652 653 654 655 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 656  = do { ctxt <- getTcSContext  dimitris committed Mar 29, 2012 657  ; if simplEqsOnly ctxt && not (isCFunEqCan wi) then  dimitris committed Mar 29, 2012 658  -- Why not just "simplEqsOnly"? See Note [SimplEqsOnly and InteractWithInerts]  dimitris committed Nov 16, 2011 659 660  return (ContinueWith wi) else  dimitris committed Mar 28, 2012 661 662 663 664  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 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689  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) } }  dimitris committed Mar 29, 2012 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719  \end{code} Note [SimplEqsOnly and InteractWithInerts] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ It may be possible when we are simplifying a RULE that we have two wanted constraints of the form: [W] c1 : F Int ~ Bool [W] c2 : F Int ~ alpha When we simplify RULES we only do equality reactions (simplEqsOnly). So the question is: are we allowed to do type family interactions? We definitely do not want to apply top-level family and dictionary instances but what should we do with the constraint set above? Suppose that c1 gets processed first and enters the inert. Remember that he will enter a CtFamHead map with (F Int) as the index. Now c2 comes along, we can't add him to the inert set since it has exactly the same key, so we'd better react him with the inert c1. In fact one might think that we should react him anyway to learn that (alpha ~ Bool). This is why we allow CFunEqCan's to perform reactions with the inerts. If we don't allow this, we will try to add both elements to the inert set and will panic! The relevant example that fails when we don't allow such family reactions is: indexed_types/should_compile/T2291.hs NB: In previous versions of TcInteract the extra guard (not (isCFunEqCan wi)) was not there but family reactions were actually happening earlier, during canonicalization. So the behaviour has not changed -- previously this tricky point was completely lost and worked by accident.  dimitris committed Mar 29, 2012 720 \begin{code}  simonpj@microsoft.com committed Sep 13, 2010 721 722 --------------------------------------------  dimitris committed Nov 16, 2011 723 724 doInteractWithInert :: Ct -> Ct -> TcS InteractResult -- Identical class constraints.  simonpj@microsoft.com committed Jan 12, 2011 725 doInteractWithInert  dimitris committed Mar 28, 2012 726 727  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 728   dimitris committed Jun 08, 2011 729  | cls1 == cls2  batterseapower committed Sep 06, 2011 730 731  = do { let pty1 = mkClassPred cls1 tys1 pty2 = mkClassPred cls2 tys2  simonpj@microsoft.com committed Nov 12, 2010 732  inert_pred_loc = (pty1, pprFlavorArising fl1)  simonpj@microsoft.com committed Feb 17, 2011 733  work_item_pred_loc = (pty2, pprFlavorArising fl2)  dimitris committed Jun 08, 2011 734   dimitris committed Nov 16, 2011 735 736 737  ; traceTcS "doInteractWithInert" (vcat [ text "inertItem = " <+> ppr inertItem , text "workItem = " <+> ppr workItem ])  dimitris committed Jun 08, 2011 738 739 740 741 742 743  ; 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 744 745 746  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 747 748 749 750 751  -- See Note [Efficient Orientation], [When improvement happens] ; case any_fundeps of -- No Functional Dependencies Nothing  dimitris committed Mar 28, 2012 752  | eqTypes tys1 tys2 -> solveOneFromTheOther "Cls/Cls" fl1 workItem  dimitris committed Nov 16, 2011 753  | otherwise -> irKeepGoing "NOP"  dimitris committed Jun 08, 2011 754 755  -- Actual Functional Dependencies  dimitris committed Nov 16, 2011 756 757  Just (_rewritten_tys2,_cos2,fd_work) -- Standard thing: create derived fds and keep on going. Importantly we don't  dimitris committed Jun 08, 2011 758  -- throw workitem back in the worklist because this can cause loops. See #5236.  dimitris committed Nov 16, 2011 759 760  -> do { emitFDWorkAsDerived fd_work (cc_depth workItem) ; irKeepGoing "Cls/Cls (new fundeps)" } -- Just keep going without droping the inert  dimitris committed Jun 08, 2011 761  }  dimitris committed Mar 28, 2012 762 763 764 765 766 767 768 769 770 771 772  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 773 774  workItem@(CIrredEvCan { cc_ty = ty2 }) | ty1 eqType ty2  dimitris committed Mar 28, 2012 775  = solveOneFromTheOther "Irred/Irred" ifl workItem  batterseapower committed Sep 10, 2011 776   simonpj@microsoft.com committed Sep 13, 2010 777 778 779 780 781 -- 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 782 doInteractWithInert (CIPCan { cc_flavor = ifl, cc_ip_nm = nm1, cc_ip_ty = ty1 })  simonpj@microsoft.com committed Sep 13, 2010 783  workItem@(CIPCan { cc_flavor = wfl, cc_ip_nm = nm2, cc_ip_ty = ty2 })  dimitris committed May 17, 2011 784  | nm1 == nm2 && isGivenOrSolved wfl && isGivenOrSolved ifl  simonpj@microsoft.com committed Sep 17, 2010 785 786 787  = -- 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 788 789  -- 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 790  irInertConsumed "IP/IP (override inert)"  simonpj@microsoft.com committed Sep 17, 2010 791   792  | nm1 == nm2 && ty1 eqType ty2  dimitris committed Mar 28, 2012 793  = solveOneFromTheOther "IP/IP" ifl workItem  simonpj@microsoft.com committed Sep 13, 2010 794   simonpj@microsoft.com committed Sep 17, 2010 795  | nm1 == nm2  simonpj@microsoft.com committed Sep 13, 2010 796  = -- See Note [When improvement happens]  dimitris committed Mar 28, 2012 797 798 799 800 801 802 803 804 805 806 807 808  do { mb_eqv <- newWantedEvVar (mkEqPred ty2 ty1) -- co :: ty2 ~ ty1, see Note [Efficient orientation] ; cv <- case mb_eqv of Fresh eqv -> do { updWorkListTcS$ extendWorkListEq $CNonCanonical { cc_flavor = Wanted new_wloc eqv , cc_depth = cc_depth workItem } ; return eqv } Cached eqv -> return eqv ; case wfl of Wanted {} -> let ip_co = mkTcTyConAppCo (ipTyCon nm1) [mkTcCoVarCo cv]  809  in do { setEvBind (ctId workItem)$  dimitris committed Mar 28, 2012 810 811 812 813 814 815 816 817 818 819  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!"  simonpj@microsoft.com committed Sep 13, 2010 820   dimitris committed Mar 28, 2012 821 822 823 824 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 825  | lhss_match  dimitris committed Mar 28, 2012 826 827  , isSolved fl1 -- Inert is solved and we can simply ignore it -- when workitem is given/solved  dimitris committed Nov 16, 2011 828 829  , isGivenOrSolved fl2 = irInertConsumed "FunEq/FunEq"  dimitris committed Mar 28, 2012 830 831 832  | lhss_match , isSolved fl2 -- Workitem is solved and we can ignore it when -- the inert is given/solved  dimitris committed Nov 16, 2011 833 834  , isGivenOrSolved fl1 = irWorkItemConsumed "FunEq/FunEq"  835  | fl1 canSolve fl2 && lhss_match  dimitris committed Mar 28, 2012 836  = do { traceTcS "interact with inerts: FunEq/FunEq" $ dimitris committed Mar 29, 2012 837 838 839 840 841 842 843 844 845 846 847 848 849  vcat [ text "workItem =" <+> ppr wi , text "inertItem=" <+> ppr ii ] ; let xev = XEvTerm xcomp xdecomp -- xcomp : [(xi2 ~ xi1)] -> (F args ~ xi2) xcomp [x] = EvCoercion (co1 mkTcTransCo mk_sym_co x) xcomp _ = panic "No more goals!" -- xdecomp : (F args ~ xi2) -> [(xi2 ~ xi1)] xdecomp x = [EvCoercion (mk_sym_co x mkTcTransCo co1)] ; xCtFlavor_cache False fl2 [mkTcEqPred xi2 xi1] xev$ what_next d2 -- Why not simply xCtFlavor? See Note [Cache-caused loops] -- Why not (mkTcEqPred xi1 xi2)? See Note [Efficient orientation]  dimitris committed Nov 16, 2011 850  ; irWorkItemConsumed "FunEq/FunEq" }  851  | fl2 canSolve fl1 && lhss_match  dimitris committed Mar 29, 2012 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866  = do { traceTcS "interact with inerts: FunEq/FunEq" $vcat [ text "workItem =" <+> ppr wi , text "inertItem=" <+> ppr ii ] ; let xev = XEvTerm xcomp xdecomp -- xcomp : [(xi2 ~ xi1)] -> [(F args ~ xi1)] xcomp [x] = EvCoercion (co2 mkTcTransCo mkTcCoVarCo x) xcomp _ = panic "No more goals!" -- xdecomp : (F args ~ xi1) -> [(xi2 ~ xi1)] xdecomp x = [EvCoercion (mkTcSymCo co2 mkTcTransCo mkTcCoVarCo x)] ; xCtFlavor_cache False fl1 [mkTcEqPred xi2 xi1] xev$ what_next d1 -- Why not simply xCtFlavor? See Note [Cache-caused loops] -- Why not (mkTcEqPred xi1 xi2)? See Note [Efficient orientation]  dimitris committed Nov 16, 2011 867  ; irInertConsumed "FunEq/FunEq"}  simonpj@microsoft.com committed Sep 13, 2010 868  where  869  lhss_match = tc1 == tc2 && eqTypes args1 args2  dimitris committed Mar 28, 2012 870 871 872 873 874 875 876 877  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)  dimitris committed Nov 16, 2011 878 879 doInteractWithInert _ _ = irKeepGoing "NOP"  dimitris committed Mar 29, 2012 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 \end{code} Note [Cache-caused loops] ~~~~~~~~~~~~~~~~~~~~~~~~~ It is very dangerous to cache a rewritten wanted family equation as 'solved' in our solved cache (which is the default behaviour or xCtFlavor), because the interaction may not be contributing towards a solution. Here is an example: Initial inert set: [W] g1 : F a ~ beta1 Work item: [W] g2 : F a ~ beta2 The work item will react with the inert yielding the _same_ inert set plus: i) Will set g2 := g1 cast g3 ii) Will add to our solved cache that [S] g2 : F a ~ beta2 iii) Will emit [W] g3 : beta1 ~ beta2 Now, the g3 work item will be spontaneously solved to [G] g3 : beta1 ~ beta2 and then it will react the item in the inert ([W] g1 : F a ~ beta1). So it will set g1 := g ; sym g3 and what is g? Well it would ideally be a new goal of type (F a ~ beta2) but remember that we have this in our solved cache, and it is ... g2! In short we created the evidence loop: g2 := g1 ; g3 g3 := refl g1 := g2 ; sym g3 To avoid this situation we do not cache as solved any workitems (or inert) which did not really made a 'step' towards proving some goal. Solved's are just an optimization so we don't lose anything in terms of completeness of solving. \begin{code}  dimitris committed Mar 28, 2012 915 916 solveOneFromTheOther :: String -- Info -> CtFlavor -- Inert  dimitris committed Nov 16, 2011 917 918 919 920 921  -> 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 922 solveOneFromTheOther info ifl workItem  simonpj@microsoft.com committed Feb 17, 2011 923  | isDerived wfl  dimitris committed Nov 16, 2011 924  = irWorkItemConsumed ("Solved[DW] " ++ info)  simonpj@microsoft.com committed Feb 17, 2011 925   simonpj@microsoft.com committed Feb 21, 2011 926 927 928  | 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 929  = irInertConsumed ("Solved[DI] " ++ info)  simonpj@microsoft.com committed Jan 12, 2011 930   dimitris committed Mar 28, 2012 931  | isSolved ifl, isGivenOrSolved wfl  dimitris committed May 17, 2011 932  -- Same if the inert is a GivenSolved -- just get rid of it  dimitris committed Nov 16, 2011 933  = irInertConsumed ("Solved[SI] " ++ info)  dimitris committed May 17, 2011 934   simonpj@microsoft.com committed Feb 21, 2011 935 936 937  | otherwise = ASSERT( ifl canSolve wfl ) -- Because of Note [The Solver Invariant], plus Derived dealt with  dimitris committed Mar 28, 2012 938  do { when (isWanted wfl)$ setEvBind wid (EvId iid)  simonpj@microsoft.com committed Feb 21, 2011 939 940  -- Overwrite the binding, if one exists -- If both are Given, we already have evidence; no need to duplicate  dimitris committed Nov 16, 2011 941  ; irWorkItemConsumed ("Solved " ++ info) }  simonpj@microsoft.com committed Sep 13, 2010 942 943  where wfl = cc_flavor workItem  944  wid = ctId workItem  dimitris committed Mar 28, 2012 945  iid = flav_evar ifl  dimitris committed Jun 08, 2011 946   simonpj@microsoft.com committed Sep 13, 2010 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 \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 964 965 966 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 967 968 969 970 971 972 973 974 975 976  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 977 and create an inert set that includes the solved (Foo [t] t) but not its superclasses:  simonpj@microsoft.com committed Sep 13, 2010 978 979 980 981  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 982 Ok, so how do we get recursive dictionaries, at all:  simonpj@microsoft.com committed Sep 13, 2010 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 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  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 our wanted d7. Now the [isRecDictEv] function in the ineration solver [case inert-given workitem-wanted] will prevent us from interacting d7 := d8 precisely because chasing the evidence of d8 leads us to an unguarded use of d7. So, no interaction happens there. Then we meet d01 and there is no recursion problem there [isRectDictEv] gives us the OK to interact and we do solve d7 := d01! Note [SUPERCLASS-LOOP 1] ~~~~~~~~~~~~~~~~~~~~~~~~ We have to be very, very careful when generating superclasses, lest we accidentally build a loop. Here's an example: class S a class S a => C a where { opc :: a -> a } class S b => D b where { opd :: b -> b } instance C Int where opc = opd instance D Int where opd = opc From (instance C Int) we get the constraint set {ds1:S Int, dd:D Int} Simplifying, we may well get: $dfCInt = :C ds1 (opd dd) dd =$dfDInt ds1 = $p1 dd Notice that we spot that we can extract ds1 from dd. Alas! Alack! We can do the same for (instance D Int):$dfDInt = :D ds2 (opc dc) dc = $dfCInt ds2 =$p1 dc And now we've defined the superclass in terms of itself. Two more nasty cases are in tcrun021 tcrun033 Solution: - Satisfy the superclass context *all by itself* (tcSimplifySuperClasses) - And do so completely; i.e. no left-over constraints to mix with the constraints arising from method declarations Note [SUPERCLASS-LOOP 2] ~~~~~~~~~~~~~~~~~~~~~~~~ We need to be careful when adding "the constaint we are trying to prove". Suppose we are *given* d1:Ord a, and want to deduce (d2:C [a]) where class Ord a => C a where instance Ord [a] => C [a] where ... Then we'll use the instance decl to deduce C [a] from Ord [a], and then add the superclasses of C [a] to avails. But we must not overwrite the binding for Ord [a] (which is obtained from Ord a) with a superclass selection or we'll just build a loop! Here's another variant, immortalised in tcrun020 class Monad m => C1 m class C1 m => C2 m x instance C2 Maybe Bool For the instance decl we need to build (C1 Maybe), and it's no good if we run around and add (C2 Maybe Bool) and its superclasses to the avails before we search for C1 Maybe. Here's another example class Eq b => Foo a b instance Eq a => Foo [a] a If we are reducing (Foo [t] t) we'll first deduce that it holds (via the instance decl). We must not then overwrite the Eq t constraint with a superclass selection! At first I had a gross hack, whereby I simply did not add superclass constraints in addWanted, though I did for addGiven and addIrred. This was sub-optimal, becuase it lost legitimate superclass sharing, and it still didn't do the job: I found a very obscure program (now tcrun021) in which improvement meant the simplifier got two bites a the cherry... so something seemed to be an Stop first time, but reducible next time. Now we implement the Right Solution, which is to check for loops directly when adding superclasses. It's a bit like the occurs check in unification. Note [Recursive instances and superclases] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider this code, which arises in the context of "Scrap Your Boilerplate with Class". class Sat a class Data ctx a instance Sat (ctx Char) => Data ctx Char instance (Sat (ctx [a]), Data ctx a) => Data ctx [a] class Data Maybe a => Foo a instance Foo t => Sat (Maybe t) instance Data Maybe a => Foo a instance Foo a => Foo [a] instance Foo [Char] In the instance for Foo [a], when generating evidence for the superclasses (ie in tcSimplifySuperClasses) we need a superclass (Data Maybe [a]). Using the instance for Data, we therefore need (Sat (Maybe [a], Data Maybe a) But we are given (Foo a), and hence its superclass (Data Maybe a). So that leaves (Sat (Maybe [a])). Using the instance for Sat means we need (Foo [a]). And that is the very dictionary we are bulding an instance for! So we must put that in the "givens". So in this case we have Given: Foo a, Foo [a] Wanted: Data Maybe [a] BUT we must *not not not* put the *superclasses* of (Foo [a]) in the givens, which is what 'addGiven' would normally do. Why? Because (Data Maybe [a]) is the superclass, so we'd "satisfy" the wanted by selecting a superclass from Foo [a], which simply makes a loop. On the other hand we *must* put the superclasses of (Foo a) in the givens, as you can see from the derivation described above. Conclusion: in the very special case of tcSimplifySuperClasses we have one 'given' (namely the "this" dictionary) whose superclasses must not be added to 'givens' by addGiven. There is a complication though. Suppose there are equalities instance (Eq a, a~b) => Num (a,b) Then we normalise the 'givens' wrt the equalities, so the original given "this" dictionary is cast to one of a different type. So it's a bit trickier than before to identify the "special" dictionary whose superclasses must not be added. See test indexed-types/should_run/EqInInstance We need a persistent property of the dictionary to record this special-ness. Current I'm using the InstLocOrigin (a bit of a hack, but cool), which is maintained by dictionary normalisation. Specifically, the InstLocOrigin is NoScOrigin then the no-superclass thing kicks in. WATCH OUT if you fiddle with InstLocOrigin! Note [MATCHING-SYNONYMS] ~~~~~~~~~~~~~~~~~~~~~~~~ When trying to match a dictionary (D tau) to a top-level instance, or a type family equation (F taus_1 ~ tau_2) to a top-level family instance, we do *not* need to expand type synonyms because the matcher will do that for us. Note [RHS-FAMILY-SYNONYMS] ~~~~~~~~~~~~~~~~~~~~~~~~~~ The RHS of a family instance is represented as yet another constructor which is like a type synonym for the real RHS the programmer declared. Eg: type instance F (a,a) = [a] Becomes: :R32 a = [a] -- internal type synonym introduced F (a,a) ~ :R32 a -- instance When we react a family instance with a type family equation in the work list we keep the synonym-using RHS without expansion.  dimitris committed Dec 22, 2011 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 %************************************************************************ %* * %* Functional dependencies, instantiation of equations %* * %************************************************************************ When we spot an equality arising from a functional dependency, we now use that equality (a "wanted") to rewrite the work-item constraint right away. This avoids two dangers Danger 1: If we send the original constraint on down the pipeline it may react with an instance declaration, and in delicate situations (when a Given overlaps with an instance) that may produce new insoluble goals: see Trac #4952 Danger 2: If we don't rewrite the constraint, it may re-react with the same thing later, and produce the same equality again --> termination worries. To achieve this required some refactoring of FunDeps.lhs (nicer now!). \begin{code} rewriteWithFunDeps :: [Equation] -> [Xi] -> WantedLoc -> TcS (Maybe ([Xi], [TcCoercion], [(EvVar,WantedLoc)])) -- Not quite a WantedEvVar unfortunately -- Because our intention could be to make -- it derived at the end of the day -- NB: The flavor of the returned EvVars will be decided by the caller -- Post: returns no trivial equalities (identities) and all EvVars returned are fresh rewriteWithFunDeps eqn_pred_locs xis wloc = do { fd_ev_poss <- mapM (instFunDepEqn wloc) eqn_pred_locs ; let fd_ev_pos :: [(Int,(EqVar,WantedLoc))] fd_ev_pos = concat fd_ev_poss (rewritten_xis, cos) = unzip (rewriteDictParams fd_ev_pos xis) ; if null fd_ev_pos then return Nothing else return (Just (rewritten_xis, cos, map snd fd_ev_pos)) } instFunDepEqn :: WantedLoc -> Equation -> TcS [(Int,(EvVar,WantedLoc))] -- Post: Returns the position index as well as the corresponding FunDep equality instFunDepEqn wl (FDEqn { fd_qtvs = qtvs, fd_eqs = eqs , fd_pred1 = d1, fd_pred2 = d2 }) = do { let tvs = varSetElems qtvs ; tvs' <- mapM instFlexiTcS tvs -- IA0_TODO: we might need to do kind substitution ; let subst = zipTopTvSubst tvs (mkTyVarTys tvs') ; foldM (do_one subst) [] eqs } where do_one subst ievs (FDEq { fd_pos = i, fd_ty_left = ty1, fd_ty_right = ty2 }) = let sty1 = Type.substTy subst ty1 sty2 = Type.substTy subst ty2 in if eqType sty1 sty2 then return ievs -- Return no trivial equalities  dimitris committed Mar 28, 2012 1343 1344 1345 1346 1347 1348 1349 1350 1351 1352  else do { mb_eqv <- newWantedEvVar (mkTcEqPred sty1 sty2) ; case mb_eqv of Fresh eqv -> return $(i,(eqv, push_ctx wl)):ievs Cached {} -> return ievs } -- We are eventually going to emit FD work back in the work list so -- it is important that we only return the /freshly created/ and not -- some existing equality! push_ctx :: WantedLoc -> WantedLoc push_ctx loc = pushErrCtxt FunDepOrigin (False, mkEqnMsg d1 d2) loc  dimitris committed Dec 22, 2011 1353 1354 1355 1356 1357 1358 1359 1360 1361 1362 1363 1364 1365 1366 1367 1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 1380 1381 1382 1383 1384 1385 1386 1387 1388  mkEqnMsg :: (TcPredType, SDoc) -> (TcPredType, SDoc) -> TidyEnv -> TcM (TidyEnv, SDoc) mkEqnMsg (pred1,from1) (pred2,from2) tidy_env = do { zpred1 <- zonkTcPredType pred1 ; zpred2 <- zonkTcPredType pred2 ; let { tpred1 = tidyType tidy_env zpred1 ; tpred2 = tidyType tidy_env zpred2 } ; let msg = vcat [ptext (sLit "When using functional dependencies to combine"), nest 2 (sep [ppr tpred1 <> comma, nest 2 from1]), nest 2 (sep [ppr tpred2 <> comma, nest 2 from2])] ; return (tidy_env, msg) } rewriteDictParams :: [(Int,(EqVar,WantedLoc))] -- A set of coercions : (pos, ty' ~ ty) -> [Type] -- A sequence of types: tys -> [(Type, TcCoercion)] -- Returns: [(ty', co : ty' ~ ty)] rewriteDictParams param_eqs tys = zipWith do_one tys [0..] where do_one :: Type -> Int -> (Type, TcCoercion) do_one ty n = case lookup n param_eqs of Just wev -> (get_fst_ty wev, mkTcCoVarCo (fst wev)) Nothing -> (ty, mkTcReflCo ty) -- Identity get_fst_ty (wev,_wloc) | Just (ty1, _) <- getEqPredTys_maybe (evVarPred wev ) = ty1 | otherwise = panic "rewriteDictParams: non equality fundep!?" emitFDWorkAsDerived :: [(EvVar,WantedLoc)] -> SubGoalDepth -> TcS () emitFDWorkAsDerived evlocs d = updWorkListTcS$ appendWorkListEqs fd_cts where fd_cts = map mk_fd_ct evlocs  dimitris committed Mar 28, 2012 1389 1390 1391  mk_fd_ct (v,wl) = CNonCanonical { cc_flavor = Derived wl (evVarPred v) , cc_depth = d }  dimitris committed Dec 22, 2011 1392 1393 1394 1395 1396 1397 1398  \end{code}  simonpj@microsoft.com committed Sep 13, 2010 1399 1400 1401 1402 1403 1404 1405 ********************************************************************************* * * The top-reaction Stage * * ********************************************************************************* \begin{code}  dimitris committed Nov 16, 2011 1406 1407 1408 1409 1410 1411 1412 1413 1414 1415  topReactionsStage :: SimplifierStage topReactionsStage workItem = tryTopReact workItem tryTopReact :: WorkItem -> TcS StopOrContinue tryTopReact wi = do { inerts <- getTcSInerts ; ctxt <- getTcSContext  dimitris committed Mar 29, 2012 1416 1417  ; if simplEqsOnly ctxt then return (ContinueWith wi)  dimitris committed Nov 16, 2011 1418  else  dimitris committed Mar 28, 2012 1419  do { tir <- doTopReact inerts wi  dimitris committed Mar 29, 2012 1420 1421 1422 1423 1424 1425 1426 1427 1428  ; case tir of NoTopInt -> return (ContinueWith wi) SomeTopInt rule what_next -> do { bumpStepCountTcS ; traceFireTcS (cc_depth wi) \$ ptext (sLit "Top react:") <+> text rule ; return what_next } } }  dimitris committed Nov 16, 2011 1429   simonpj@microsoft.com committed Sep 13, 2010 1430 data TopInter