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 Pair
  19 import Name
  20 import CoreSyn
  21 import CoreSubst
  22 import CoqPass ( coqPassCoreToString, coqPassCoreToCore )
  23 import PprCore
  24 import DsMonad
  25 import DsExpr
  26 import DsBinds
  27 import DsForeign
  28 import DsExpr           ()      -- Forces DsExpr to be compiled; DsBinds only
  29                                 -- depends on DsExpr.hi-boot.
  30 import Module
  31 import RdrName
  32 import NameSet
  33 import NameEnv
  34 import Rules
  35 import CoreMonad        ( endPass, CoreToDo(..) )
  36 import ErrUtils
  37 import Outputable
  38 import SrcLoc
  39 import Coverage
  40 import Util
  41 import MonadUtils
  42 import OrdList
  43 import Data.List
  44 import Data.IORef
  45 import PrelNames
  46 import UniqSupply
  47 import UniqFM
  48 import CoreFVs
  49 import Type
  50 import Coercion
  51 \end{code}
  52
  53 %************************************************************************
  54 %*                                                                      *
  55 %*              The main function: deSugar
  56 %*                                                                      *
  57 %************************************************************************
  58
  59 \begin{code}
  60
  61 -- | Main entry point to the desugarer.
  62 deSugar :: HscEnv -> ModLocation -> TcGblEnv -> IO (Messages, Maybe ModGuts)
  63 -- Can modify PCS by faulting in more declarations
  64
  65 deSugar hsc_env
  66         mod_loc
  67         tcg_env@(TcGblEnv { tcg_mod          = mod,
  68                             tcg_src          = hsc_src,
  69                             tcg_type_env     = type_env,
  70                             tcg_imports      = imports,
  71                             tcg_exports      = exports,
  72                             tcg_keep         = keep_var,
  73                             tcg_rdr_env      = rdr_env,
  74                             tcg_fix_env      = fix_env,
  75                             tcg_inst_env     = inst_env,
  76                             tcg_fam_inst_env = fam_inst_env,
  77                             tcg_warns        = warns,
  78                             tcg_anns         = anns,
  79                             tcg_binds        = binds,
  80                             tcg_imp_specs    = imp_specs,
  81                             tcg_ev_binds     = ev_binds,
  82                             tcg_fords        = fords,
  83                             tcg_rules        = rules,
  84                             tcg_vects        = vects,
  85                             tcg_insts        = insts,
  86                             tcg_fam_insts    = fam_insts,
  87                             tcg_hpc          = other_hpc_info })
  88
  89   = do  { let dflags = hsc_dflags hsc_env
  90         ; showPass dflags "Desugar"
  91
  92         -- Desugar the program
  93         ; let export_set = availsToNameSet exports
  94         ; let auto_scc = mkAutoScc dflags mod export_set
  95         ; let target = hscTarget dflags
  96         ; let hpcInfo = emptyHpcInfo other_hpc_info
  97         ; (msgs, mb_res)
  98               <- case target of
  99                    HscNothing ->
 100                        return (emptyMessages,
 101                                Just ([], nilOL, [], [], NoStubs, hpcInfo, emptyModBreaks, undefined, 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                                     , undefined
 115                                     , undefined
 116                                     , undefined
 117                                     , undefined
 118                                     , undefined
 119                                     , undefined
 120                                     , undefined
 121                                     , undefined
 122                                     , undefined
 123                                     , undefined
 124                                     , undefined
 125                                     , undefined
 126                                ))
 127                    _        -> do
 128                      (binds_cvr,ds_hpc_info, modBreaks)
 129                          <- if (opt_Hpc
 130                                   || target == HscInterpreted)
 131                                && (not (isHsBoot hsc_src))
 132                               then addCoverageTicksToBinds dflags mod mod_loc
 133                                                            (typeEnvTyCons type_env) binds
 134                               else return (binds, hpcInfo, emptyModBreaks)
 135                      initDs hsc_env mod rdr_env type_env $ do
 136                        do { ds_ev_binds <- dsEvBinds ev_binds
 137                           ; core_prs <- dsTopLHsBinds auto_scc binds_cvr
 138                           ; (spec_prs, spec_rules) <- dsImpSpecs imp_specs
 139                           ; (ds_fords, foreign_prs) <- dsForeigns fords
 140                           ; ds_rules <- mapMaybeM dsRule rules
 141                           ; ds_vects <- mapM dsVect vects
 142                           ; hetmet_brak <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_brak_name else return undefined
 143                           ; hetmet_esc  <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_esc_name  else return undefined
 144                           ; hetmet_flatten <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_flatten_name else return undefined
 145                           ; hetmet_unflatten <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_unflatten_name else return undefined
 146                           ; hetmet_flattened_id <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_flattened_id_name else return undefined
 147                           ; hetmet_PGArrow <- if dopt Opt_F_coqpass dflags then dsLookupTyCon hetmet_PGArrow_name else return undefined
 148                           ; hetmet_PGArrow_unit <- if dopt Opt_F_coqpass dflags then dsLookupTyCon hetmet_PGArrow_unit_name else return undefined
 149                           ; hetmet_PGArrow_tensor <- if dopt Opt_F_coqpass dflags then dsLookupTyCon hetmet_PGArrow_tensor_name else return undefined
 150                           ; hetmet_PGArrow_exponent <- if dopt Opt_F_coqpass dflags then dsLookupTyCon hetmet_PGArrow_exponent_name else return undefined
 151                           ; hetmet_pga_id <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_id_name else return undefined
 152                           ; hetmet_pga_comp <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_comp_name else return undefined
 153                           ; hetmet_pga_first <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_first_name else return undefined
 154                           ; hetmet_pga_second <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_second_name else return undefined
 155                           ; hetmet_pga_cancell <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_cancell_name else return undefined
 156                           ; hetmet_pga_cancelr <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_cancelr_name else return undefined
 157                           ; hetmet_pga_uncancell <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_uncancell_name else return undefined
 158                           ; hetmet_pga_uncancelr <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_uncancelr_name else return undefined
 159                           ; hetmet_pga_assoc <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_assoc_name else return undefined
 160                           ; hetmet_pga_unassoc <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_unassoc_name else return undefined
 161                           ; hetmet_pga_copy <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_copy_name else return undefined
 162                           ; hetmet_pga_drop <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_drop_name else return undefined
 163                           ; hetmet_pga_swap <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_swap_name else return undefined
 164                           ; hetmet_pga_applyl <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_applyl_name else return undefined
 165                           ; hetmet_pga_applyr <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_applyr_name else return undefined
 166                           ; hetmet_pga_curryl <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_curryl_name else return undefined
 167                           ; hetmet_pga_curryr <- if dopt Opt_F_coqpass dflags then dsLookupGlobalId hetmet_pga_curryr_name else return undefined
 168                           ; let hpc_init
 169                                   | opt_Hpc   = hpcInitCode mod ds_hpc_info
 170                                   | otherwise = empty
 171                           ; return ( ds_ev_binds
 172                                    , foreign_prs `appOL` core_prs `appOL` spec_prs
 173                                    , spec_rules ++ ds_rules, ds_vects
 174                                    , ds_fords `appendStubC` hpc_init
 175                                    , ds_hpc_info, modBreaks, hetmet_brak, hetmet_esc
 176                                    , hetmet_flatten
 177                                    , hetmet_unflatten
 178                                    , hetmet_flattened_id
 179                                    , hetmet_PGArrow
 180                                    , hetmet_PGArrow_unit
 181                                    , hetmet_PGArrow_tensor
 182                                    , hetmet_PGArrow_exponent
 183                                    , hetmet_pga_id
 184                                    , hetmet_pga_comp
 185                                    , hetmet_pga_first
 186                                    , hetmet_pga_second
 187                                    , hetmet_pga_cancell
 188                                    , hetmet_pga_cancelr
 189                                    , hetmet_pga_uncancell
 190                                    , hetmet_pga_uncancelr
 191                                    , hetmet_pga_assoc
 192                                    , hetmet_pga_unassoc
 193                                    , hetmet_pga_copy
 194                                    , hetmet_pga_drop
 195                                    , hetmet_pga_swap
 196                                    , hetmet_pga_applyl
 197                                    , hetmet_pga_applyr
 198                                    , hetmet_pga_curryl
 199                                    , hetmet_pga_curryr
 200                                    ) }
 201
 202         ; case mb_res of {
 203            Nothing -> return (msgs, Nothing) ;
 204            Just (ds_ev_binds, all_prs, all_rules, ds_vects, ds_fords,ds_hpc_info, modBreaks
 205                                    , hetmet_brak, hetmet_esc
 206                                    , hetmet_flatten
 207                                    , hetmet_unflatten
 208                                    , hetmet_flattened_id
 209                                    , hetmet_PGArrow
 210                                    , hetmet_PGArrow_unit
 211                                    , hetmet_PGArrow_tensor
 212                                    , hetmet_PGArrow_exponent
 213                                    , hetmet_pga_id
 214                                    , hetmet_pga_comp
 215                                    , hetmet_pga_first
 216                                    , hetmet_pga_second
 217                                    , hetmet_pga_cancell
 218                                    , hetmet_pga_cancelr
 219                                    , hetmet_pga_uncancell
 220                                    , hetmet_pga_uncancelr
 221                                    , hetmet_pga_assoc
 222                                    , hetmet_pga_unassoc
 223                                    , hetmet_pga_copy
 224                                    , hetmet_pga_drop
 225                                    , hetmet_pga_swap
 226                                    , hetmet_pga_applyl
 227                                    , hetmet_pga_applyr
 228                                    , hetmet_pga_curryl
 229                                    , hetmet_pga_curryr) -> do
 230
 231         {       -- Add export flags to bindings
 232           keep_alive <- readIORef keep_var
 233         ; let (rules_for_locals, rules_for_imps)
 234                    = partition isLocalRule all_rules
 235               final_prs = addExportFlagsAndRules target
 236                               export_set keep_alive rules_for_locals (fromOL all_prs)
 237
 238               final_pgm = simplifyBinds $ combineEvBinds ds_ev_binds final_prs
 239         -- Notice that we put the whole lot in a big Rec, even the foreign binds
 240         -- When compiling PrelFloat, which defines data Float = F# Float#
 241         -- we want F# to be in scope in the foreign marshalling code!
 242         -- You might think it doesn't matter, but the simplifier brings all top-level
 243         -- things into the in-scope set before simplifying; so we get no unfolding for F#!
 244
 245         -- Lint result if necessary, and print
 246         ; dumpIfSet_dyn dflags Opt_D_dump_ds "Desugared, before opt" $
 247                (vcat [ pprCoreBindings final_pgm
 248                      , pprRules rules_for_imps ])
 249
 250         ; (final_pgm', rules_for_imps') <- if dopt Opt_F_simpleopt_before_flatten dflags
 251                                             then simpleOptPgm dflags final_pgm rules_for_imps
 252                                             else return (final_pgm, rules_for_imps)
 253
 254         ; ds_binds <- if dopt Opt_F_coqpass dflags
 255                        then do { us <- mkSplitUniqSupply '~'
 256                                ; let do_flatten   = dopt Opt_F_flatten dflags
 257                                ; let do_skolemize = dopt Opt_F_skolemize dflags
 258                                ; return (coqPassCoreToCore
 259                                              do_flatten
 260                                              do_skolemize
 261                                              hetmet_brak
 262                                              hetmet_esc
 263                                              hetmet_flatten
 264                                              hetmet_unflatten
 265                                              hetmet_flattened_id
 266                                              us
 267                                              final_pgm'
 268                                              hetmet_PGArrow
 269                                              hetmet_PGArrow_unit
 270                                              hetmet_PGArrow_tensor
 271                                              hetmet_PGArrow_exponent
 272                                              hetmet_pga_id
 273                                              hetmet_pga_comp
 274                                              hetmet_pga_first
 275                                              hetmet_pga_second
 276                                              hetmet_pga_cancell
 277                                              hetmet_pga_cancelr
 278                                              hetmet_pga_uncancell
 279                                              hetmet_pga_uncancelr
 280                                              hetmet_pga_assoc
 281                                              hetmet_pga_unassoc
 282                                              hetmet_pga_copy
 283                                              hetmet_pga_drop
 284                                              hetmet_pga_swap
 285                                              hetmet_pga_applyl
 286                                              hetmet_pga_applyr
 287                                              hetmet_pga_curryl
 288                                              hetmet_pga_curryr)
 289                                }
 290                        else return final_pgm
 291
 292         ; (ds_binds', ds_rules_for_imps) <- if dopt Opt_F_simpleopt_before_flatten dflags
 293                                             then return (ds_binds, rules_for_imps')
 294                                             else simpleOptPgm dflags ds_binds rules_for_imps'
 295                          -- The simpleOptPgm gets rid of type
 296                          -- bindings plus any stupid dead code
 297
 298         ; dumpIfSet_dyn dflags Opt_D_dump_proofs "Coq Pass Output" $ text $ coqPassCoreToString ds_binds'
 299
 300         ; dumpIfSet_dyn dflags Opt_D_coqpass "After Coq Pass" (text $ showSDoc $ pprCoreBindings ds_binds')
 301
 302         ; endPass dflags CoreDesugar ds_binds' ds_rules_for_imps
 303
 304         ; let used_names = mkUsedNames tcg_env
 305         ; deps <- mkDependencies tcg_env
 306
 307         ; let mod_guts = ModGuts {
 308                 mg_module       = mod,
 309                 mg_boot         = isHsBoot hsc_src,
 310                 mg_exports      = exports,
 311                 mg_deps         = deps,
 312                 mg_used_names   = used_names,
 313                 mg_dir_imps     = imp_mods imports,
 314                 mg_rdr_env      = rdr_env,
 315                 mg_fix_env      = fix_env,
 316                 mg_warns        = warns,
 317                 mg_anns         = anns,
 318                 mg_types        = type_env,
 319                 mg_insts        = insts,
 320                 mg_fam_insts    = fam_insts,
 321                 mg_inst_env     = inst_env,
 322                 mg_fam_inst_env = fam_inst_env,
 323                 mg_rules        = ds_rules_for_imps,
 324                 mg_binds        = ds_binds',
 325                 mg_foreign      = ds_fords,
 326                 mg_hpc_info     = ds_hpc_info,
 327                 mg_modBreaks    = modBreaks,
 328                 mg_vect_decls   = ds_vects,
 329                 mg_vect_info    = noVectInfo
 330               }
 331         ; return (msgs, Just mod_guts)
 332         }}}
 333
 334 dsImpSpecs :: [LTcSpecPrag] -> DsM (OrdList (Id,CoreExpr), [CoreRule])
 335 dsImpSpecs imp_specs
 336  = do { spec_prs <- mapMaybeM (dsSpec Nothing) imp_specs
 337       ; let (spec_binds, spec_rules) = unzip spec_prs
 338       ; return (concatOL spec_binds, spec_rules) }
 339
 340 combineEvBinds :: [DsEvBind] -> [(Id,CoreExpr)] -> [CoreBind]
 341 -- Top-level bindings can include coercion bindings, but not via superclasses
 342 -- See Note [Top-level evidence]
 343 combineEvBinds [] val_prs
 344   = [Rec val_prs]
 345 combineEvBinds (LetEvBind (NonRec b r) : bs) val_prs
 346   | isId b    = combineEvBinds bs ((b,r):val_prs)
 347   | otherwise = NonRec b r : combineEvBinds bs val_prs
 348 combineEvBinds (LetEvBind (Rec prs) : bs) val_prs
 349   = combineEvBinds bs (prs ++ val_prs)
 350 combineEvBinds (CaseEvBind x _ _ : _) _
 351   = pprPanic "topEvBindPairs" (ppr x)
 352 \end{code}
 353
 354 Note [Top-level evidence]
 355 ~~~~~~~~~~~~~~~~~~~~~~~~~
 356 Top-level evidence bindings may be mutually recursive with the top-level value
 357 bindings, so we must put those in a Rec.  But we can't put them *all* in a Rec
 358 because the occurrence analyser doesn't teke account of type/coercion variables
 359 when computing dependencies.
 360
 361 So we pull out the type/coercion variables (which are in dependency order),
 362 and Rec the rest.
 363
 364
 365 \begin{code}
 366 mkAutoScc :: DynFlags -> Module -> NameSet -> AutoScc
 367 mkAutoScc dflags mod exports
 368   | not opt_SccProfilingOn      -- No profiling
 369   = NoSccs
 370     -- Add auto-scc on all top-level things
 371   | dopt Opt_AutoSccsOnAllToplevs dflags
 372   = AddSccs mod (\id -> not $ isDerivedOccName $ getOccName id)
 373     -- See #1641.  This is pretty yucky, but I can't see a better way
 374     -- to identify compiler-generated Ids, and at least this should
 375     -- catch them all.
 376     -- Only on exported things
 377   | dopt Opt_AutoSccsOnExportedToplevs dflags
 378   = AddSccs mod (\id -> idName id `elemNameSet` exports)
 379   | otherwise
 380   = NoSccs
 381
 382 deSugarExpr :: HscEnv
 383             -> Module -> GlobalRdrEnv -> TypeEnv
 384             -> LHsExpr Id
 385             -> IO (Messages, Maybe CoreExpr)
 386 -- Prints its own errors; returns Nothing if error occurred
 387
 388 deSugarExpr hsc_env this_mod rdr_env type_env tc_expr = do
 389     let dflags = hsc_dflags hsc_env
 390     showPass dflags "Desugar"
 391
 392     -- Do desugaring
 393     (msgs, mb_core_expr) <- initDs hsc_env this_mod rdr_env type_env $
 394                                    dsLExpr tc_expr
 395
 396     case mb_core_expr of
 397       Nothing   -> return (msgs, Nothing)
 398       Just expr -> do
 399
 400         -- Dump output
 401         dumpIfSet_dyn dflags Opt_D_dump_ds "Desugared" (pprCoreExpr expr)
 402
 403         return (msgs, Just expr)
 404 \end{code}
 405
 406 %************************************************************************
 407 %*                                                                      *
 408 %*              Add rules and export flags to binders
 409 %*                                                                      *
 410 %************************************************************************
 411
 412 \begin{code}
 413 addExportFlagsAndRules
 414     :: HscTarget -> NameSet -> NameSet -> [CoreRule]
 415     -> [(Id, t)] -> [(Id, t)]
 416 addExportFlagsAndRules target exports keep_alive rules prs
 417   = mapFst add_one prs
 418   where
 419     add_one bndr = add_rules name (add_export name bndr)
 420        where
 421          name = idName bndr
 422
 423     ---------- Rules --------
 424         -- See Note [Attach rules to local ids]
 425         -- NB: the binder might have some existing rules,
 426         -- arising from specialisation pragmas
 427     add_rules name bndr
 428         | Just rules <- lookupNameEnv rule_base name
 429         = bndr `addIdSpecialisations` rules
 430         | otherwise
 431         = bndr
 432     rule_base = extendRuleBaseList emptyRuleBase rules
 433
 434     ---------- Export flag --------
 435     -- See Note [Adding export flags]
 436     add_export name bndr
 437         | dont_discard name = setIdExported bndr
 438         | otherwise         = bndr
 439
 440     dont_discard :: Name -> Bool
 441     dont_discard name = is_exported name
 442                      || name `elemNameSet` keep_alive
 443
 444         -- In interactive mode, we don't want to discard any top-level
 445         -- entities at all (eg. do not inline them away during
 446         -- simplification), and retain them all in the TypeEnv so they are
 447         -- available from the command line.
 448         --
 449         -- isExternalName separates the user-defined top-level names from those
 450         -- introduced by the type checker.
 451     is_exported :: Name -> Bool
 452     is_exported | target == HscInterpreted = isExternalName
 453                 | otherwise                = (`elemNameSet` exports)
 454 \end{code}
 455
 456
 457 Note [Adding export flags]
 458 ~~~~~~~~~~~~~~~~~~~~~~~~~~
 459 Set the no-discard flag if either
 460         a) the Id is exported
 461         b) it's mentioned in the RHS of an orphan rule
 462         c) it's in the keep-alive set
 463
 464 It means that the binding won't be discarded EVEN if the binding
 465 ends up being trivial (v = w) -- the simplifier would usually just
 466 substitute w for v throughout, but we don't apply the substitution to
 467 the rules (maybe we should?), so this substitution would make the rule
 468 bogus.
 469
 470 You might wonder why exported Ids aren't already marked as such;
 471 it's just because the type checker is rather busy already and
 472 I didn't want to pass in yet another mapping.
 473
 474 Note [Attach rules to local ids]
 475 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 476 Find the rules for locally-defined Ids; then we can attach them
 477 to the binders in the top-level bindings
 478
 479 Reason
 480   - It makes the rules easier to look up
 481   - It means that transformation rules and specialisations for
 482     locally defined Ids are handled uniformly
 483   - It keeps alive things that are referred to only from a rule
 484     (the occurrence analyser knows about rules attached to Ids)
 485   - It makes sure that, when we apply a rule, the free vars
 486     of the RHS are more likely to be in scope
 487   - The imported rules are carried in the in-scope set
 488     which is extended on each iteration by the new wave of
 489     local binders; any rules which aren't on the binding will
 490     thereby get dropped
 491
 492
 493 %************************************************************************
 494 %*                                                                      *
 495 %*              Desugaring transformation rules
 496 %*                                                                      *
 497 %************************************************************************
 498
 499 \begin{code}
 500 dsRule :: LRuleDecl Id -> DsM (Maybe CoreRule)
 501 dsRule (L loc (HsRule name act vars lhs _tv_lhs rhs _fv_rhs))
 502   = putSrcSpanDs loc $
 503     do  { let bndrs' = [var | RuleBndr (L _ var) <- vars]
 504
 505         ; lhs' <- unsetOptM Opt_EnableRewriteRules $
 506                   unsetOptM Opt_WarnIdentities $
 507                   dsLExpr lhs   -- Note [Desugaring RULE left hand sides]
 508
 509         ; rhs' <- dsLExpr rhs
 510
 511         -- Substitute the dict bindings eagerly,
 512         -- and take the body apart into a (f args) form
 513         ; case decomposeRuleLhs bndrs' lhs' of {
 514                 Left msg -> do { warnDs msg; return Nothing } ;
 515                 Right (final_bndrs, fn_id, args) -> do
 516
 517         { let is_local = isLocalId fn_id
 518                 -- NB: isLocalId is False of implicit Ids.  This is good becuase
 519                 -- we don't want to attach rules to the bindings of implicit Ids,
 520                 -- because they don't show up in the bindings until just before code gen
 521               fn_name   = idName fn_id
 522               final_rhs = simpleOptExpr rhs'    -- De-crap it
 523               rule      = mkRule False {- Not auto -} is_local
 524                                  name act fn_name final_bndrs args final_rhs
 525         ; return (Just rule)
 526         } } }
 527 \end{code}
 528
 529 Note [Desugaring RULE left hand sides]
 530 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 531 For the LHS of a RULE we do *not* want to desugar
 532     [x]   to    build (\cn. x `c` n)
 533 We want to leave explicit lists simply as chains
 534 of cons's. We can achieve that slightly indirectly by
 535 switching off EnableRewriteRules.  See DsExpr.dsExplicitList.
 536
 537 That keeps the desugaring of list comprehensions simple too.
 538
 539
 540
 541 Nor do we want to warn of conversion identities on the LHS;
 542 the rule is precisly to optimise them:
 543   {-# RULES "fromRational/id" fromRational = id :: Rational -> Rational #-}
 544
 545
 546 %************************************************************************
 547 %*                                                                      *
 548 %*              Desugaring vectorisation declarations
 549 %*                                                                      *
 550 %************************************************************************
 551
 552 \begin{code}
 553 dsVect :: LVectDecl Id -> DsM CoreVect
 554 dsVect (L loc (HsVect v rhs))
 555   = putSrcSpanDs loc $
 556     do { rhs' <- fmapMaybeM dsLExpr rhs
 557        ; return $ Vect (unLoc v) rhs'
 558            }
 559 -- dsVect (L loc (HsVect v Nothing))
 560 --   = return $ Vect v Nothing
 561 -- dsVect (L loc (HsVect v (Just rhs)))
 562 --   = putSrcSpanDs loc $
 563 --     do { rhs' <- dsLExpr rhs
 564 --        ; return $ Vect v (Just rhs')
 565 --       }
 566 \end{code}
 567
 568
 569
 570 \begin{code}
 571 --
 572 -- Simplification routines run before the flattener.  We can't use
 573 -- simpleOptPgm -- it doesn't preserve the order of subexpressions or
 574 -- let-binding groups.
 575 --
 576 simplify :: Expr CoreBndr -> Expr CoreBndr
 577 simplify (Var v)                 = Var v
 578 simplify (App e1 e2)             = App (simplify e1) (simplify e2)
 579 simplify (Lit lit)               = Lit lit
 580 simplify (Note note e)           = Note note (simplify e)
 581 simplify (Cast e co)             = if eqType (fst $ unPair $ coercionKind co) (snd $ unPair $ coercionKind co)
 582                                        then simplify e
 583                                        else Cast (simplify e) co
 584 simplify (Lam v e)               = Lam v (simplify e)
 585 simplify (Case e b ty as)        = Case (simplify e) b ty (map (\(a,b,e) -> (a,b,simplify e)) as)
 586 simplify (Let bind body)         = foldr Let (simplify body) (simplifyBind bind)
 587 simplify (Type t)                = Type t
 588 simplify (Coercion co)           = Coercion co
 589
 590 simplifyBind :: Bind CoreBndr -> [Bind CoreBndr]
 591 simplifyBind (NonRec b e)             = [NonRec b (simplify e)]
 592 simplifyBind (Rec [])                 = []
 593 simplifyBind (Rec (rbs@((b,e):rbs'))) =
 594     if or $ map (\x -> elemUFM x (exprFreeIds e)) (map fst rbs)
 595     then [Rec (map (\(v,e) -> (v,simplify e)) rbs)]
 596     else (NonRec b (simplify e)):(simplifyBind $ Rec rbs')
 597
 598 simplifyBinds = concatMap simplifyBind
 599 \end{code}