2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
6 The Desugarer: turning HsSyn into Core.
9 module Desugar ( deSugar, deSugarExpr ) where
11 import TysWiredIn (unitDataConId)
27 import DsExpr () -- Forces DsExpr to be compiled; DsBinds only
28 -- depends on DsExpr.hi-boot.
34 import CoreMonad ( endPass, CoreToDo(..) )
45 import Control.Exception ( catch, ErrorCall, Exception(..) )
48 %************************************************************************
50 %* The main function: deSugar
52 %************************************************************************
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
61 tcg_env@(TcGblEnv { tcg_mod = mod,
63 tcg_type_env = type_env,
64 tcg_imports = imports,
65 tcg_exports = exports,
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,
74 tcg_imp_specs = imp_specs,
75 tcg_ev_binds = ev_binds,
79 tcg_fam_insts = fam_insts,
80 tcg_hpc = other_hpc_info })
82 = do { let dflags = hsc_dflags hsc_env
83 ; showPass dflags "Desugar"
85 -- Desugar the program
86 ; let export_set = availsToNameSet exports
87 ; let auto_scc = mkAutoScc dflags mod export_set
88 ; let target = hscTarget dflags
89 ; let hpcInfo = emptyHpcInfo other_hpc_info
93 return (emptyMessages,
94 Just ([], nilOL, [], NoStubs, hpcInfo, emptyModBreaks))
96 (binds_cvr,ds_hpc_info, modBreaks)
98 || target == HscInterpreted)
99 && (not (isHsBoot hsc_src))
100 then addCoverageTicksToBinds dflags mod mod_loc
101 (typeEnvTyCons type_env) binds
102 else return (binds, hpcInfo, emptyModBreaks)
103 initDs hsc_env mod rdr_env type_env $ do
104 do { ds_ev_binds <- dsEvBinds ev_binds
105 ; core_prs <- dsTopLHsBinds auto_scc binds_cvr
106 ; (spec_prs, spec_rules) <- dsImpSpecs imp_specs
107 ; (ds_fords, foreign_prs) <- dsForeigns fords
108 ; rules <- mapMaybeM dsRule rules
109 ; return ( ds_ev_binds
110 , foreign_prs `appOL` core_prs `appOL` spec_prs
111 , spec_rules ++ rules
112 , ds_fords, ds_hpc_info, modBreaks) }
115 Nothing -> return (msgs, Nothing) ;
116 Just (ds_ev_binds, all_prs, all_rules, ds_fords,ds_hpc_info, modBreaks) -> do
118 { -- Add export flags to bindings
119 keep_alive <- readIORef keep_var
120 ; let (rules_for_locals, rules_for_imps)
121 = partition isLocalRule all_rules
122 final_prs = addExportFlagsAndRules target
123 export_set keep_alive rules_for_locals (fromOL all_prs)
125 final_pgm = combineEvBinds ds_ev_binds final_prs
126 -- Notice that we put the whole lot in a big Rec, even the foreign binds
127 -- When compiling PrelFloat, which defines data Float = F# Float#
128 -- we want F# to be in scope in the foreign marshalling code!
129 -- You might think it doesn't matter, but the simplifier brings all top-level
130 -- things into the in-scope set before simplifying; so we get no unfolding for F#!
132 -- Lint result if necessary, and print
133 ; dumpIfSet_dyn dflags Opt_D_dump_ds "Desugared, before opt" $
134 (vcat [ pprCoreBindings final_pgm
135 , pprRules rules_for_imps ])
137 ; (ds_binds, ds_rules_for_imps) <- simpleOptPgm dflags final_pgm rules_for_imps
138 -- The simpleOptPgm gets rid of type
139 -- bindings plus any stupid dead code
141 ; dumpIfSet_dyn dflags Opt_D_dump_proof "input to flattener" (text $ showSDoc $ pprCoreBindings ds_binds)
142 ; let uhandler (err::ErrorCall)
143 = dumpIfSet_dyn dflags Opt_D_dump_proof "System FC Proof"
144 (text $ "\\begin{verbatim}\n" ++
146 "\\end{verbatim}\n\n")
147 in (dumpIfSet_dyn dflags Opt_D_dump_proof "System FC Proof" $
148 (vcat (map (\ bind -> let e = case bind of
150 Rec lve -> Let (Rec lve) (Var unitDataConId)
151 in text $ "\\begin{verbatim}\n" ++
152 (showSDoc $ pprCoreBindings ds_binds) ++
153 "\\end{verbatim}\n\n" ++
155 (core2proofAndShow e) ++
157 ) ds_binds))) `Control.Exception.catch` uhandler
159 ; endPass dflags CoreDesugar ds_binds ds_rules_for_imps
161 ; let used_names = mkUsedNames tcg_env
162 ; deps <- mkDependencies tcg_env
164 ; let mod_guts = ModGuts {
166 mg_boot = isHsBoot hsc_src,
167 mg_exports = exports,
169 mg_used_names = used_names,
170 mg_dir_imps = imp_mods imports,
171 mg_rdr_env = rdr_env,
172 mg_fix_env = fix_env,
177 mg_fam_insts = fam_insts,
178 mg_inst_env = inst_env,
179 mg_fam_inst_env = fam_inst_env,
180 mg_rules = ds_rules_for_imps,
182 mg_foreign = ds_fords,
183 mg_hpc_info = ds_hpc_info,
184 mg_modBreaks = modBreaks,
185 mg_vect_info = noVectInfo
187 ; return (msgs, Just mod_guts)
190 dsImpSpecs :: [LTcSpecPrag] -> DsM (OrdList (Id,CoreExpr), [CoreRule])
192 = do { spec_prs <- mapMaybeM (dsSpec Nothing) imp_specs
193 ; let (spec_binds, spec_rules) = unzip spec_prs
194 ; return (concatOL spec_binds, spec_rules) }
196 combineEvBinds :: [DsEvBind] -> [(Id,CoreExpr)] -> [CoreBind]
197 -- Top-level bindings can include coercion bindings, but not via superclasses
198 -- See Note [Top-level evidence]
199 combineEvBinds [] val_prs
201 combineEvBinds (LetEvBind (NonRec b r) : bs) val_prs
202 | isId b = combineEvBinds bs ((b,r):val_prs)
203 | otherwise = NonRec b r : combineEvBinds bs val_prs
204 combineEvBinds (LetEvBind (Rec prs) : bs) val_prs
205 = combineEvBinds bs (prs ++ val_prs)
206 combineEvBinds (CaseEvBind x _ _ : _) _
207 = pprPanic "topEvBindPairs" (ppr x)
210 Note [Top-level evidence]
211 ~~~~~~~~~~~~~~~~~~~~~~~~~
212 Top-level evidence bindings may be mutually recursive with the top-level value
213 bindings, so we must put those in a Rec. But we can't put them *all* in a Rec
214 because the occurrence analyser doesn't teke account of type/coercion variables
215 when computing dependencies.
217 So we pull out the type/coercion variables (which are in dependency order),
222 mkAutoScc :: DynFlags -> Module -> NameSet -> AutoScc
223 mkAutoScc dflags mod exports
224 | not opt_SccProfilingOn -- No profiling
226 -- Add auto-scc on all top-level things
227 | dopt Opt_AutoSccsOnAllToplevs dflags
228 = AddSccs mod (\id -> not $ isDerivedOccName $ getOccName id)
229 -- See #1641. This is pretty yucky, but I can't see a better way
230 -- to identify compiler-generated Ids, and at least this should
232 -- Only on exported things
233 | dopt Opt_AutoSccsOnExportedToplevs dflags
234 = AddSccs mod (\id -> idName id `elemNameSet` exports)
238 deSugarExpr :: HscEnv
239 -> Module -> GlobalRdrEnv -> TypeEnv
241 -> IO (Messages, Maybe CoreExpr)
242 -- Prints its own errors; returns Nothing if error occurred
244 deSugarExpr hsc_env this_mod rdr_env type_env tc_expr = do
245 let dflags = hsc_dflags hsc_env
246 showPass dflags "Desugarz"
249 (msgs, mb_core_expr) <- initDs hsc_env this_mod rdr_env type_env $
253 Nothing -> return (msgs, Nothing)
258 dumpIfSet_dyn dflags Opt_D_dump_ds "Desugared" (text $ "$$\n"++(core2proofAndShow expr)++"$$\n")
261 return (msgs, Just expr)
264 %************************************************************************
266 %* Add rules and export flags to binders
268 %************************************************************************
271 addExportFlagsAndRules
272 :: HscTarget -> NameSet -> NameSet -> [CoreRule]
273 -> [(Id, t)] -> [(Id, t)]
274 addExportFlagsAndRules target exports keep_alive rules prs
277 add_one bndr = add_rules name (add_export name bndr)
281 ---------- Rules --------
282 -- See Note [Attach rules to local ids]
283 -- NB: the binder might have some existing rules,
284 -- arising from specialisation pragmas
286 | Just rules <- lookupNameEnv rule_base name
287 = bndr `addIdSpecialisations` rules
290 rule_base = extendRuleBaseList emptyRuleBase rules
292 ---------- Export flag --------
293 -- See Note [Adding export flags]
295 | dont_discard name = setIdExported bndr
298 dont_discard :: Name -> Bool
299 dont_discard name = is_exported name
300 || name `elemNameSet` keep_alive
302 -- In interactive mode, we don't want to discard any top-level
303 -- entities at all (eg. do not inline them away during
304 -- simplification), and retain them all in the TypeEnv so they are
305 -- available from the command line.
307 -- isExternalName separates the user-defined top-level names from those
308 -- introduced by the type checker.
309 is_exported :: Name -> Bool
310 is_exported | target == HscInterpreted = isExternalName
311 | otherwise = (`elemNameSet` exports)
315 Note [Adding export flags]
316 ~~~~~~~~~~~~~~~~~~~~~~~~~~
317 Set the no-discard flag if either
318 a) the Id is exported
319 b) it's mentioned in the RHS of an orphan rule
320 c) it's in the keep-alive set
322 It means that the binding won't be discarded EVEN if the binding
323 ends up being trivial (v = w) -- the simplifier would usually just
324 substitute w for v throughout, but we don't apply the substitution to
325 the rules (maybe we should?), so this substitution would make the rule
328 You might wonder why exported Ids aren't already marked as such;
329 it's just because the type checker is rather busy already and
330 I didn't want to pass in yet another mapping.
332 Note [Attach rules to local ids]
333 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
334 Find the rules for locally-defined Ids; then we can attach them
335 to the binders in the top-level bindings
338 - It makes the rules easier to look up
339 - It means that transformation rules and specialisations for
340 locally defined Ids are handled uniformly
341 - It keeps alive things that are referred to only from a rule
342 (the occurrence analyser knows about rules attached to Ids)
343 - It makes sure that, when we apply a rule, the free vars
344 of the RHS are more likely to be in scope
345 - The imported rules are carried in the in-scope set
346 which is extended on each iteration by the new wave of
347 local binders; any rules which aren't on the binding will
351 %************************************************************************
353 %* Desugaring transformation rules
355 %************************************************************************
358 dsRule :: LRuleDecl Id -> DsM (Maybe CoreRule)
359 dsRule (L loc (HsRule name act vars lhs _tv_lhs rhs _fv_rhs))
361 do { let bndrs' = [var | RuleBndr (L _ var) <- vars]
363 ; lhs' <- unsetOptM Opt_EnableRewriteRules $
364 unsetOptM Opt_WarnIdentities $
365 dsLExpr lhs -- Note [Desugaring RULE left hand sides]
367 ; rhs' <- dsLExpr rhs
369 -- Substitute the dict bindings eagerly,
370 -- and take the body apart into a (f args) form
371 ; case decomposeRuleLhs bndrs' lhs' of {
372 Left msg -> do { warnDs msg; return Nothing } ;
373 Right (final_bndrs, fn_id, args) -> do
375 { let is_local = isLocalId fn_id
376 -- NB: isLocalId is False of implicit Ids. This is good becuase
377 -- we don't want to attach rules to the bindings of implicit Ids,
378 -- because they don't show up in the bindings until just before code gen
379 fn_name = idName fn_id
380 final_rhs = simpleOptExpr rhs' -- De-crap it
381 rule = mkRule False {- Not auto -} is_local
382 name act fn_name final_bndrs args final_rhs
387 Note [Desugaring RULE left hand sides]
388 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
389 For the LHS of a RULE we do *not* want to desugar
390 [x] to build (\cn. x `c` n)
391 We want to leave explicit lists simply as chains
392 of cons's. We can achieve that slightly indirectly by
393 switching off EnableRewriteRules. See DsExpr.dsExplicitList.
395 That keeps the desugaring of list comprehensions simple too.
397 Nor do we want to warn of conversion identities on the LHS;
398 the rule is precisly to optimise them:
399 {-# RULES "fromRational/id" fromRational = id :: Rational -> Rational #-}