compiler/deSugar/Desugar.lhs

   1 %
   2 % (c) The University of Glasgow 2006
   3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
   4 %
   5
   6 The Desugarer: turning HsSyn into Core.
   7
   8 \begin{code}
   9 module Desugar ( deSugar, deSugarExpr ) where
  10
  11 import DynFlags
  12 import StaticFlags
  13 import HscTypes
  14 import HsSyn
  15 import TcRnTypes
  16 import MkIface
  17 import Id
  18 import Name
  19 import CoreSyn
  20 import CoreSubst
  21 import CoqPass ( coqPassCoreToString, coqPassCoreToCore )
  22 import PprCore
  23 import DsMonad
  24 import DsExpr
  25 import DsBinds
  26 import DsForeign
  27 import DsExpr           ()      -- Forces DsExpr to be compiled; DsBinds only
  28                                 -- depends on DsExpr.hi-boot.
  29 import Module
  30 import RdrName
  31 import NameSet
  32 import NameEnv
  33 import Rules
  34 import CoreMonad        ( endPass, CoreToDo(..) )
  35 import ErrUtils
  36 import Outputable
  37 import SrcLoc
  38 import Coverage
  39 import Util
  40 import MonadUtils
  41 import OrdList
  42 import Data.List
  43 import Data.IORef
  44 import PrelNames
  45 import UniqSupply
  46 \end{code}
  47
  48 %************************************************************************
  49 %*                                                                      *
  50 %*              The main function: deSugar
  51 %*                                                                      *
  52 %************************************************************************
  53
  54 \begin{code}
  55 -- | Main entry point to the desugarer.
  56 deSugar :: HscEnv -> ModLocation -> TcGblEnv -> IO (Messages, Maybe ModGuts)
  57 -- Can modify PCS by faulting in more declarations
  58
  59 deSugar hsc_env
  60         mod_loc
  61         tcg_env@(TcGblEnv { tcg_mod          = mod,
  62                             tcg_src          = hsc_src,
  63                             tcg_type_env     = type_env,
  64                             tcg_imports      = imports,
  65                             tcg_exports      = exports,
  66                             tcg_keep         = keep_var,
  67                             tcg_rdr_env      = rdr_env,
  68                             tcg_fix_env      = fix_env,
  69                             tcg_inst_env     = inst_env,
  70                             tcg_fam_inst_env = fam_inst_env,
  71                             tcg_warns        = warns,
  72                             tcg_anns         = anns,
  73                             tcg_binds        = binds,
  74                             tcg_imp_specs    = imp_specs,
  75                             tcg_ev_binds     = ev_binds,
  76                             tcg_fords        = fords,
  77                             tcg_rules        = rules,
  78                             tcg_vects        = vects,
  79                             tcg_insts        = insts,
  80                             tcg_fam_insts    = fam_insts,
  81                             tcg_hpc          = other_hpc_info })
  82
  83   = do  { let dflags = hsc_dflags hsc_env
  84         ; showPass dflags "Desugar"
  85
  86         -- Desugar the program
  87         ; let export_set = availsToNameSet exports
  88         ; let auto_scc = mkAutoScc dflags mod export_set
  89         ; let target = hscTarget dflags
  90         ; let hpcInfo = emptyHpcInfo other_hpc_info
  91         ; (msgs, mb_res)
  92               <- case target of
  93                    HscNothing ->
  94                        return (emptyMessages,
  95                                Just ([], nilOL, [], [], NoStubs, hpcInfo, emptyModBreaks, undefined, undefined
  96                                     , undefined
  97                                     , undefined
  98                                     , undefined
  99                                     , undefined
 100                                     , undefined
 101                                     , undefined
 102                                     , undefined
 103                                     , undefined
 104                                     , undefined
 105                                     , undefined
 106                                     , undefined
 107                                     , undefined
 108                                     , undefined
 109                                     , undefined
 110                                     , undefined
 111                                     , undefined
 112                                     , undefined
 113                                     , undefined
 114                                ))
 115                    _        -> do
 116                      (binds_cvr,ds_hpc_info, modBreaks)
 117                          <- if (opt_Hpc
 118                                   || target == HscInterpreted)
 119                                && (not (isHsBoot hsc_src))
 120                               then addCoverageTicksToBinds dflags mod mod_loc
 121                                                            (typeEnvTyCons type_env) binds
 122                               else return (binds, hpcInfo, emptyModBreaks)
 123                      initDs hsc_env mod rdr_env type_env $ do
 124                        do { ds_ev_binds <- dsEvBinds ev_binds
 125                           ; core_prs <- dsTopLHsBinds auto_scc binds_cvr
 126                           ; (spec_prs, spec_rules) <- dsImpSpecs imp_specs
 127                           ; (ds_fords, foreign_prs) <- dsForeigns fords
 128                           ; ds_rules <- mapMaybeM dsRule rules
 129                           ; ds_vects <- mapM dsVect vects
 130                           ; hetmet_brak <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_brak_name else return undefined
 131                           ; hetmet_esc  <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_esc_name  else return undefined
 132                           ; hetmet_PGArrow <- if dopt Opt_F_coqpass dflags then dsLookupTyCon hetmet_PGArrow_name else return undefined
 133                           ; hetmet_pga_id <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_id_name else return undefined
 134                           ; hetmet_pga_comp <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_comp_name else return undefined
 135                           ; hetmet_pga_first <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_first_name else return undefined
 136                           ; hetmet_pga_second <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_second_name else return undefined
 137                           ; hetmet_pga_cancell <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_cancell_name else return undefined
 138                           ; hetmet_pga_cancelr <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_cancelr_name else return undefined
 139                           ; hetmet_pga_uncancell <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_uncancell_name else return undefined
 140                           ; hetmet_pga_uncancelr <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_uncancelr_name else return undefined
 141                           ; hetmet_pga_assoc <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_assoc_name else return undefined
 142                           ; hetmet_pga_unassoc <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_unassoc_name else return undefined
 143                           ; hetmet_pga_copy <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_copy_name else return undefined
 144                           ; hetmet_pga_drop <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_drop_name else return undefined
 145                           ; hetmet_pga_swap <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_swap_name else return undefined
 146                           ; hetmet_pga_applyl <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_applyl_name else return undefined
 147                           ; hetmet_pga_applyr <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_applyr_name else return undefined
 148                           ; hetmet_pga_curryl <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_curryl_name else return undefined
 149                           ; hetmet_pga_curryr <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_curryr_name else return undefined
 150                           ; let hpc_init
 151                                   | opt_Hpc   = hpcInitCode mod ds_hpc_info
 152                                   | otherwise = empty
 153                           ; return ( ds_ev_binds
 154                                    , foreign_prs `appOL` core_prs `appOL` spec_prs
 155                                    , spec_rules ++ ds_rules, ds_vects
 156                                    , ds_fords `appendStubC` hpc_init
 157                                    , ds_hpc_info, modBreaks, hetmet_brak, hetmet_esc
 158                                    , hetmet_PGArrow
 159                                    , hetmet_pga_id
 160                                    , hetmet_pga_comp
 161                                    , hetmet_pga_first
 162                                    , hetmet_pga_second
 163                                    , hetmet_pga_cancell
 164                                    , hetmet_pga_cancelr
 165                                    , hetmet_pga_uncancell
 166                                    , hetmet_pga_uncancelr
 167                                    , hetmet_pga_assoc
 168                                    , hetmet_pga_unassoc
 169                                    , hetmet_pga_copy
 170                                    , hetmet_pga_drop
 171                                    , hetmet_pga_swap
 172                                    , hetmet_pga_applyl
 173                                    , hetmet_pga_applyr
 174                                    , hetmet_pga_curryl
 175                                    , hetmet_pga_curryr
 176                                    ) }
 177
 178         ; case mb_res of {
 179            Nothing -> return (msgs, Nothing) ;
 180            Just (ds_ev_binds, all_prs, all_rules, ds_vects, ds_fords,ds_hpc_info, modBreaks, hetmet_brak, hetmet_esc
 181                                    , hetmet_PGArrow
 182                                    , hetmet_pga_id
 183                                    , hetmet_pga_comp
 184                                    , hetmet_pga_first
 185                                    , hetmet_pga_second
 186                                    , hetmet_pga_cancell
 187                                    , hetmet_pga_cancelr
 188                                    , hetmet_pga_uncancell
 189                                    , hetmet_pga_uncancelr
 190                                    , hetmet_pga_assoc
 191                                    , hetmet_pga_unassoc
 192                                    , hetmet_pga_copy
 193                                    , hetmet_pga_drop
 194                                    , hetmet_pga_swap
 195                                    , hetmet_pga_applyl
 196                                    , hetmet_pga_applyr
 197                                    , hetmet_pga_curryl
 198                                    , hetmet_pga_curryr) -> do
 199
 200         {       -- Add export flags to bindings
 201           keep_alive <- readIORef keep_var
 202         ; let (rules_for_locals, rules_for_imps)
 203                    = partition isLocalRule all_rules
 204               final_prs = addExportFlagsAndRules target
 205                               export_set keep_alive rules_for_locals (fromOL all_prs)
 206
 207               final_pgm = combineEvBinds ds_ev_binds final_prs
 208         -- Notice that we put the whole lot in a big Rec, even the foreign binds
 209         -- When compiling PrelFloat, which defines data Float = F# Float#
 210         -- we want F# to be in scope in the foreign marshalling code!
 211         -- You might think it doesn't matter, but the simplifier brings all top-level
 212         -- things into the in-scope set before simplifying; so we get no unfolding for F#!
 213
 214         -- Lint result if necessary, and print
 215         ; dumpIfSet_dyn dflags Opt_D_dump_ds "Desugared, before opt" $
 216                (vcat [ pprCoreBindings final_pgm
 217                      , pprRules rules_for_imps ])
 218
 219         ; (ds_binds, ds_rules_for_imps) <- simpleOptPgm dflags final_pgm rules_for_imps
 220                          -- The simpleOptPgm gets rid of type
 221                          -- bindings plus any stupid dead code
 222
 223         ; ds_binds' <- if dopt Opt_F_coqpass dflags
 224                        then do { us <- mkSplitUniqSupply '~'
 225                                ; return (coqPassCoreToCore
 226                                              hetmet_brak
 227                                              hetmet_esc
 228                                              us
 229                                              ds_binds
 230                                              hetmet_PGArrow
 231                                              hetmet_pga_id
 232                                              hetmet_pga_comp
 233                                              hetmet_pga_first
 234                                              hetmet_pga_second
 235                                              hetmet_pga_cancell
 236                                              hetmet_pga_cancelr
 237                                              hetmet_pga_uncancell
 238                                              hetmet_pga_uncancelr
 239                                              hetmet_pga_assoc
 240                                              hetmet_pga_unassoc
 241                                              hetmet_pga_copy
 242                                              hetmet_pga_drop
 243                                              hetmet_pga_swap
 244                                              hetmet_pga_applyl
 245                                              hetmet_pga_applyr
 246                                              hetmet_pga_curryl
 247                                              hetmet_pga_curryr)
 248                                }
 249                        else return ds_binds
 250
 251         ; dumpIfSet_dyn dflags Opt_D_coqpass "Coq Pass Output" $ text $ coqPassCoreToString ds_binds'
 252
 253         ; dumpIfSet_dyn dflags Opt_D_dump_coqpass "After Coq Pass" (text $ showSDoc $ pprCoreBindings ds_binds')
 254
 255         ; endPass dflags CoreDesugar ds_binds' ds_rules_for_imps
 256
 257         ; let used_names = mkUsedNames tcg_env
 258         ; deps <- mkDependencies tcg_env
 259
 260         ; let mod_guts = ModGuts {
 261                 mg_module       = mod,
 262                 mg_boot         = isHsBoot hsc_src,
 263                 mg_exports      = exports,
 264                 mg_deps         = deps,
 265                 mg_used_names   = used_names,
 266                 mg_dir_imps     = imp_mods imports,
 267                 mg_rdr_env      = rdr_env,
 268                 mg_fix_env      = fix_env,
 269                 mg_warns        = warns,
 270                 mg_anns         = anns,
 271                 mg_types        = type_env,
 272                 mg_insts        = insts,
 273                 mg_fam_insts    = fam_insts,
 274                 mg_inst_env     = inst_env,
 275                 mg_fam_inst_env = fam_inst_env,
 276                 mg_rules        = ds_rules_for_imps,
 277                 mg_binds        = ds_binds',
 278                 mg_foreign      = ds_fords,
 279                 mg_hpc_info     = ds_hpc_info,
 280                 mg_modBreaks    = modBreaks,
 281                 mg_vect_decls   = ds_vects,
 282                 mg_vect_info    = noVectInfo
 283               }
 284         ; return (msgs, Just mod_guts)
 285         }}}
 286
 287 dsImpSpecs :: [LTcSpecPrag] -> DsM (OrdList (Id,CoreExpr), [CoreRule])
 288 dsImpSpecs imp_specs
 289  = do { spec_prs <- mapMaybeM (dsSpec Nothing) imp_specs
 290       ; let (spec_binds, spec_rules) = unzip spec_prs
 291       ; return (concatOL spec_binds, spec_rules) }
 292
 293 combineEvBinds :: [DsEvBind] -> [(Id,CoreExpr)] -> [CoreBind]
 294 -- Top-level bindings can include coercion bindings, but not via superclasses
 295 -- See Note [Top-level evidence]
 296 combineEvBinds [] val_prs
 297   = [Rec val_prs]
 298 combineEvBinds (LetEvBind (NonRec b r) : bs) val_prs
 299   | isId b    = combineEvBinds bs ((b,r):val_prs)
 300   | otherwise = NonRec b r : combineEvBinds bs val_prs
 301 combineEvBinds (LetEvBind (Rec prs) : bs) val_prs
 302   = combineEvBinds bs (prs ++ val_prs)
 303 combineEvBinds (CaseEvBind x _ _ : _) _
 304   = pprPanic "topEvBindPairs" (ppr x)
 305 \end{code}
 306
 307 Note [Top-level evidence]
 308 ~~~~~~~~~~~~~~~~~~~~~~~~~
 309 Top-level evidence bindings may be mutually recursive with the top-level value
 310 bindings, so we must put those in a Rec.  But we can't put them *all* in a Rec
 311 because the occurrence analyser doesn't teke account of type/coercion variables
 312 when computing dependencies.
 313
 314 So we pull out the type/coercion variables (which are in dependency order),
 315 and Rec the rest.
 316
 317
 318 \begin{code}
 319 mkAutoScc :: DynFlags -> Module -> NameSet -> AutoScc
 320 mkAutoScc dflags mod exports
 321   | not opt_SccProfilingOn      -- No profiling
 322   = NoSccs
 323     -- Add auto-scc on all top-level things
 324   | dopt Opt_AutoSccsOnAllToplevs dflags
 325   = AddSccs mod (\id -> not $ isDerivedOccName $ getOccName id)
 326     -- See #1641.  This is pretty yucky, but I can't see a better way
 327     -- to identify compiler-generated Ids, and at least this should
 328     -- catch them all.
 329     -- Only on exported things
 330   | dopt Opt_AutoSccsOnExportedToplevs dflags
 331   = AddSccs mod (\id -> idName id `elemNameSet` exports)
 332   | otherwise
 333   = NoSccs
 334
 335 deSugarExpr :: HscEnv
 336             -> Module -> GlobalRdrEnv -> TypeEnv
 337             -> LHsExpr Id
 338             -> IO (Messages, Maybe CoreExpr)
 339 -- Prints its own errors; returns Nothing if error occurred
 340
 341 deSugarExpr hsc_env this_mod rdr_env type_env tc_expr = do
 342     let dflags = hsc_dflags hsc_env
 343     showPass dflags "Desugar"
 344
 345     -- Do desugaring
 346     (msgs, mb_core_expr) <- initDs hsc_env this_mod rdr_env type_env $
 347                                    dsLExpr tc_expr
 348
 349     case mb_core_expr of
 350       Nothing   -> return (msgs, Nothing)
 351       Just expr -> do
 352
 353         -- Dump output
 354         dumpIfSet_dyn dflags Opt_D_dump_ds "Desugared" (pprCoreExpr expr)
 355
 356         return (msgs, Just expr)
 357 \end{code}
 358
 359 %************************************************************************
 360 %*                                                                      *
 361 %*              Add rules and export flags to binders
 362 %*                                                                      *
 363 %************************************************************************
 364
 365 \begin{code}
 366 addExportFlagsAndRules
 367     :: HscTarget -> NameSet -> NameSet -> [CoreRule]
 368     -> [(Id, t)] -> [(Id, t)]
 369 addExportFlagsAndRules target exports keep_alive rules prs
 370   = mapFst add_one prs
 371   where
 372     add_one bndr = add_rules name (add_export name bndr)
 373        where
 374          name = idName bndr
 375
 376     ---------- Rules --------
 377         -- See Note [Attach rules to local ids]
 378         -- NB: the binder might have some existing rules,
 379         -- arising from specialisation pragmas
 380     add_rules name bndr
 381         | Just rules <- lookupNameEnv rule_base name
 382         = bndr `addIdSpecialisations` rules
 383         | otherwise
 384         = bndr
 385     rule_base = extendRuleBaseList emptyRuleBase rules
 386
 387     ---------- Export flag --------
 388     -- See Note [Adding export flags]
 389     add_export name bndr
 390         | dont_discard name = setIdExported bndr
 391         | otherwise         = bndr
 392
 393     dont_discard :: Name -> Bool
 394     dont_discard name = is_exported name
 395                      || name `elemNameSet` keep_alive
 396
 397         -- In interactive mode, we don't want to discard any top-level
 398         -- entities at all (eg. do not inline them away during
 399         -- simplification), and retain them all in the TypeEnv so they are
 400         -- available from the command line.
 401         --
 402         -- isExternalName separates the user-defined top-level names from those
 403         -- introduced by the type checker.
 404     is_exported :: Name -> Bool
 405     is_exported | target == HscInterpreted = isExternalName
 406                 | otherwise                = (`elemNameSet` exports)
 407 \end{code}
 408
 409
 410 Note [Adding export flags]
 411 ~~~~~~~~~~~~~~~~~~~~~~~~~~
 412 Set the no-discard flag if either
 413         a) the Id is exported
 414         b) it's mentioned in the RHS of an orphan rule
 415         c) it's in the keep-alive set
 416
 417 It means that the binding won't be discarded EVEN if the binding
 418 ends up being trivial (v = w) -- the simplifier would usually just
 419 substitute w for v throughout, but we don't apply the substitution to
 420 the rules (maybe we should?), so this substitution would make the rule
 421 bogus.
 422
 423 You might wonder why exported Ids aren't already marked as such;
 424 it's just because the type checker is rather busy already and
 425 I didn't want to pass in yet another mapping.
 426
 427 Note [Attach rules to local ids]
 428 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 429 Find the rules for locally-defined Ids; then we can attach them
 430 to the binders in the top-level bindings
 431
 432 Reason
 433   - It makes the rules easier to look up
 434   - It means that transformation rules and specialisations for
 435     locally defined Ids are handled uniformly
 436   - It keeps alive things that are referred to only from a rule
 437     (the occurrence analyser knows about rules attached to Ids)
 438   - It makes sure that, when we apply a rule, the free vars
 439     of the RHS are more likely to be in scope
 440   - The imported rules are carried in the in-scope set
 441     which is extended on each iteration by the new wave of
 442     local binders; any rules which aren't on the binding will
 443     thereby get dropped
 444
 445
 446 %************************************************************************
 447 %*                                                                      *
 448 %*              Desugaring transformation rules
 449 %*                                                                      *
 450 %************************************************************************
 451
 452 \begin{code}
 453 dsRule :: LRuleDecl Id -> DsM (Maybe CoreRule)
 454 dsRule (L loc (HsRule name act vars lhs _tv_lhs rhs _fv_rhs))
 455   = putSrcSpanDs loc $
 456     do  { let bndrs' = [var | RuleBndr (L _ var) <- vars]
 457
 458         ; lhs' <- unsetOptM Opt_EnableRewriteRules $
 459                   unsetOptM Opt_WarnIdentities $
 460                   dsLExpr lhs   -- Note [Desugaring RULE left hand sides]
 461
 462         ; rhs' <- dsLExpr rhs
 463
 464         -- Substitute the dict bindings eagerly,
 465         -- and take the body apart into a (f args) form
 466         ; case decomposeRuleLhs bndrs' lhs' of {
 467                 Left msg -> do { warnDs msg; return Nothing } ;
 468                 Right (final_bndrs, fn_id, args) -> do
 469
 470         { let is_local = isLocalId fn_id
 471                 -- NB: isLocalId is False of implicit Ids.  This is good becuase
 472                 -- we don't want to attach rules to the bindings of implicit Ids,
 473                 -- because they don't show up in the bindings until just before code gen
 474               fn_name   = idName fn_id
 475               final_rhs = simpleOptExpr rhs'    -- De-crap it
 476               rule      = mkRule False {- Not auto -} is_local
 477                                  name act fn_name final_bndrs args final_rhs
 478         ; return (Just rule)
 479         } } }
 480 \end{code}
 481
 482 Note [Desugaring RULE left hand sides]
 483 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 484 For the LHS of a RULE we do *not* want to desugar
 485     [x]   to    build (\cn. x `c` n)
 486 We want to leave explicit lists simply as chains
 487 of cons's. We can achieve that slightly indirectly by
 488 switching off EnableRewriteRules.  See DsExpr.dsExplicitList.
 489
 490 That keeps the desugaring of list comprehensions simple too.
 491
 492 Nor do we want to warn of conversion identities on the LHS;
 493 the rule is precisly to optimise them:
 494   {-# RULES "fromRational/id" fromRational = id :: Rational -> Rational #-}
 495
 496
 497 %************************************************************************
 498 %*                                                                      *
 499 %*              Desugaring vectorisation declarations
 500 %*                                                                      *
 501 %************************************************************************
 502
 503 \begin{code}
 504 dsVect :: LVectDecl Id -> DsM CoreVect
 505 dsVect (L loc (HsVect v rhs))
 506   = putSrcSpanDs loc $
 507     do { rhs' <- fmapMaybeM dsLExpr rhs
 508        ; return $ Vect (unLoc v) rhs'
 509            }
 510 -- dsVect (L loc (HsVect v Nothing))
 511 --   = return $ Vect v Nothing
 512 -- dsVect (L loc (HsVect v (Just rhs)))
 513 --   = putSrcSpanDs loc $
 514 --     do { rhs' <- dsLExpr rhs
 515 --        ; return $ Vect v (Just rhs')
 516 --       }
 517 \end{code}