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 #include "HsVersions.h"
27 import DsExpr () -- Forces DsExpr to be compiled; DsBinds only
28 -- depends on DsExpr.hi-boot.
50 %************************************************************************
52 %* The main function: deSugar
54 %************************************************************************
57 deSugar :: HscEnv -> ModLocation -> TcGblEnv -> IO (Maybe ModGuts)
58 -- Can modify PCS by faulting in more declarations
62 tcg_env@(TcGblEnv { tcg_mod = mod,
64 tcg_type_env = type_env,
65 tcg_imports = imports,
66 tcg_exports = exports,
68 tcg_inst_uses = dfun_uses_var,
71 tcg_rdr_env = rdr_env,
72 tcg_fix_env = fix_env,
73 tcg_fam_inst_env = fam_inst_env,
74 tcg_deprecs = deprecs,
79 tcg_fam_insts = fam_insts })
81 = do { let dflags = hsc_dflags hsc_env
82 ; showPass dflags "Desugar"
84 -- Desugar the program
85 ; let export_set = availsToNameSet exports
86 ; let auto_scc = mkAutoScc mod export_set
87 ; let target = hscTarget dflags
88 ; mb_res <- case target of
89 HscNothing -> return (Just ([], [], NoStubs, noHpcInfo, emptyModBreaks))
90 _ -> do (binds_cvr,ds_hpc_info, modBreaks)
91 <- if opt_Hpc || target == HscInterpreted
92 then addCoverageTicksToBinds dflags mod mod_loc binds
93 else return (binds, noHpcInfo, emptyModBreaks)
94 initDs hsc_env mod rdr_env type_env $ do
95 { core_prs <- dsTopLHsBinds auto_scc binds_cvr
96 ; (ds_fords, foreign_prs) <- dsForeigns fords
97 ; let all_prs = foreign_prs ++ core_prs
98 local_bndrs = mkVarSet (map fst all_prs)
99 ; ds_rules <- mappM (dsRule mod local_bndrs) rules
100 ; return (all_prs, catMaybes ds_rules, ds_fords, ds_hpc_info, modBreaks)
103 Nothing -> return Nothing ;
104 Just (all_prs, ds_rules, ds_fords,ds_hpc_info, modBreaks) -> do
106 { -- Add export flags to bindings
107 keep_alive <- readIORef keep_var
108 ; let final_prs = addExportFlags target export_set
109 keep_alive all_prs ds_rules
110 ds_binds = [Rec final_prs]
111 -- Notice that we put the whole lot in a big Rec, even the foreign binds
112 -- When compiling PrelFloat, which defines data Float = F# Float#
113 -- we want F# to be in scope in the foreign marshalling code!
114 -- You might think it doesn't matter, but the simplifier brings all top-level
115 -- things into the in-scope set before simplifying; so we get no unfolding for F#!
117 -- Lint result if necessary
118 ; endPass dflags "Desugar" Opt_D_dump_ds ds_binds
121 ; doIfSet (dopt Opt_D_dump_ds dflags)
122 (printDump (ppr_ds_rules ds_rules))
124 ; dfun_uses <- readIORef dfun_uses_var -- What dfuns are used
125 ; th_used <- readIORef th_var -- Whether TH is used
126 ; let used_names = allUses dus `unionNameSets` dfun_uses
127 pkgs | th_used = insertList thPackageId (imp_dep_pkgs imports)
128 | otherwise = imp_dep_pkgs imports
130 dep_mods = eltsUFM (delFromUFM (imp_dep_mods imports) (moduleName mod))
131 -- M.hi-boot can be in the imp_dep_mods, but we must remove
132 -- it before recording the modules on which this one depends!
133 -- (We want to retain M.hi-boot in imp_dep_mods so that
134 -- loadHiBootInterface can see if M's direct imports depend
135 -- on M.hi-boot, and hence that we should do the hi-boot consistency
138 dir_imp_mods = imp_mods imports
140 ; usages <- mkUsageInfo hsc_env dir_imp_mods dep_mods used_names
143 -- Modules don't compare lexicographically usually,
144 -- but we want them to do so here.
145 le_mod :: Module -> Module -> Bool
146 le_mod m1 m2 = moduleNameFS (moduleName m1)
147 <= moduleNameFS (moduleName m2)
148 le_dep_mod :: (ModuleName, IsBootInterface) -> (ModuleName, IsBootInterface) -> Bool
149 le_dep_mod (m1,_) (m2,_) = moduleNameFS m1 <= moduleNameFS m2
151 deps = Deps { dep_mods = sortLe le_dep_mod dep_mods,
152 dep_pkgs = sortLe (<=) pkgs,
153 dep_orphs = sortLe le_mod (imp_orphs imports),
154 dep_finsts = sortLe le_mod (imp_finsts imports) }
155 -- sort to get into canonical order
159 mg_boot = isHsBoot hsc_src,
160 mg_exports = exports,
163 mg_dir_imps = [m | (m,_,_) <- moduleEnvElts dir_imp_mods],
164 mg_rdr_env = rdr_env,
165 mg_fix_env = fix_env,
166 mg_deprecs = deprecs,
169 mg_fam_insts = fam_insts,
170 mg_fam_inst_env = fam_inst_env,
173 mg_foreign = ds_fords,
174 mg_hpc_info = ds_hpc_info,
175 mg_modBreaks = modBreaks }
176 ; return (Just mod_guts)
179 mkAutoScc :: Module -> NameSet -> AutoScc
180 mkAutoScc mod exports
181 | not opt_SccProfilingOn -- No profiling
183 | opt_AutoSccsOnAllToplevs -- Add auto-scc on all top-level things
184 = AddSccs mod (\id -> True)
185 | opt_AutoSccsOnExportedToplevs -- Only on exported things
186 = AddSccs mod (\id -> idName id `elemNameSet` exports)
191 deSugarExpr :: HscEnv
192 -> Module -> GlobalRdrEnv -> TypeEnv
194 -> IO (Maybe CoreExpr)
195 -- Prints its own errors; returns Nothing if error occurred
197 deSugarExpr hsc_env this_mod rdr_env type_env tc_expr
198 = do { let dflags = hsc_dflags hsc_env
199 ; showPass dflags "Desugar"
202 ; mb_core_expr <- initDs hsc_env this_mod rdr_env type_env $
205 ; case mb_core_expr of {
206 Nothing -> return Nothing ;
210 dumpIfSet_dyn dflags Opt_D_dump_ds "Desugared" (pprCoreExpr expr)
212 ; return (Just expr) } } }
215 -- Set the no-discard flag if either
216 -- a) the Id is exported
217 -- b) it's mentioned in the RHS of an orphan rule
218 -- c) it's in the keep-alive set
220 -- It means that the binding won't be discarded EVEN if the binding
221 -- ends up being trivial (v = w) -- the simplifier would usually just
222 -- substitute w for v throughout, but we don't apply the substitution to
223 -- the rules (maybe we should?), so this substitution would make the rule
226 -- You might wonder why exported Ids aren't already marked as such;
227 -- it's just because the type checker is rather busy already and
228 -- I didn't want to pass in yet another mapping.
230 addExportFlags target exports keep_alive prs rules
231 = [(add_export bndr, rhs) | (bndr,rhs) <- prs]
234 | dont_discard bndr = setIdExported bndr
237 orph_rhs_fvs = unionVarSets [ ruleRhsFreeVars rule
239 not (isLocalRule rule) ]
240 -- A non-local rule keeps alive the free vars of its right-hand side.
241 -- (A "non-local" is one whose head function is not locally defined.)
242 -- Local rules are (later, after gentle simplification)
243 -- attached to the Id, and that keeps the rhs free vars alive.
245 dont_discard bndr = is_exported name
246 || name `elemNameSet` keep_alive
247 || bndr `elemVarSet` orph_rhs_fvs
251 -- In interactive mode, we don't want to discard any top-level
252 -- entities at all (eg. do not inline them away during
253 -- simplification), and retain them all in the TypeEnv so they are
254 -- available from the command line.
256 -- isExternalName separates the user-defined top-level names from those
257 -- introduced by the type checker.
258 is_exported :: Name -> Bool
259 is_exported | target == HscInterpreted = isExternalName
260 | otherwise = (`elemNameSet` exports)
262 ppr_ds_rules [] = empty
264 = text "" $$ text "-------------- DESUGARED RULES -----------------" $$
270 %************************************************************************
272 %* Desugaring transformation rules
274 %************************************************************************
277 dsRule :: Module -> IdSet -> LRuleDecl Id -> DsM (Maybe CoreRule)
278 dsRule mod in_scope (L loc (HsRule name act vars lhs tv_lhs rhs fv_rhs))
280 do { let bndrs = [var | RuleBndr (L _ var) <- vars]
281 ; lhs' <- dsLExpr lhs
282 ; rhs' <- dsLExpr rhs
284 ; case decomposeRuleLhs bndrs lhs' of {
285 Nothing -> do { warnDs msg; return Nothing } ;
286 Just (bndrs', fn_id, args) -> do
288 -- Substitute the dict bindings eagerly,
289 -- and take the body apart into a (f args) form
290 { let local_rule = isLocalId fn_id
291 -- NB: isLocalId is False of implicit Ids. This is good becuase
292 -- we don't want to attach rules to the bindings of implicit Ids,
293 -- because they don't show up in the bindings until just before code gen
294 fn_name = idName fn_id
296 rule = Rule { ru_name = name, ru_fn = fn_name, ru_act = act,
297 ru_bndrs = bndrs', ru_args = args, ru_rhs = rhs',
298 ru_rough = roughTopNames args,
299 ru_local = local_rule }
303 msg = hang (ptext SLIT("RULE left-hand side too complicated to desugar; ignored"))