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"
28 import DsExpr () -- Forces DsExpr to be compiled; DsBinds only
29 -- depends on DsExpr.hi-boot.
48 %************************************************************************
50 %* The main function: deSugar
52 %************************************************************************
55 deSugar :: HscEnv -> ModLocation -> TcGblEnv -> IO (Maybe ModGuts)
56 -- Can modify PCS by faulting in more declarations
60 tcg_env@(TcGblEnv { tcg_mod = mod,
62 tcg_type_env = type_env,
63 tcg_imports = imports,
64 tcg_exports = exports,
66 tcg_rdr_env = rdr_env,
67 tcg_fix_env = fix_env,
68 tcg_inst_env = inst_env,
69 tcg_fam_inst_env = fam_inst_env,
70 tcg_deprecs = deprecs,
75 tcg_fam_insts = fam_insts,
76 tcg_hpc = other_hpc_info })
78 = do { let dflags = hsc_dflags hsc_env
79 ; showPass dflags "Desugar"
81 -- Desugar the program
82 ; let export_set = availsToNameSet exports
83 ; let auto_scc = mkAutoScc mod export_set
84 ; let target = hscTarget dflags
85 ; let hpcInfo = emptyHpcInfo other_hpc_info
86 ; mb_res <- case target of
87 HscNothing -> return (Just ([], [], NoStubs, hpcInfo, emptyModBreaks))
88 _ -> do (binds_cvr,ds_hpc_info, modBreaks)
90 || target == HscInterpreted)
91 && (not (isHsBoot hsc_src))
92 then addCoverageTicksToBinds dflags mod mod_loc (typeEnvTyCons type_env) binds
93 else return (binds, hpcInfo, 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 ; ds_rules <- mappM dsRule rules
99 ; return (all_prs, catMaybes ds_rules, ds_fords, ds_hpc_info, modBreaks)
102 Nothing -> return Nothing ;
103 Just (all_prs, ds_rules, ds_fords,ds_hpc_info, modBreaks) -> do
105 { -- Add export flags to bindings
106 keep_alive <- readIORef keep_var
107 ; let final_prs = addExportFlags target export_set
108 keep_alive all_prs ds_rules
109 ds_binds = [Rec final_prs]
110 -- Notice that we put the whole lot in a big Rec, even the foreign binds
111 -- When compiling PrelFloat, which defines data Float = F# Float#
112 -- we want F# to be in scope in the foreign marshalling code!
113 -- You might think it doesn't matter, but the simplifier brings all top-level
114 -- things into the in-scope set before simplifying; so we get no unfolding for F#!
116 -- Lint result if necessary
117 ; endPass dflags "Desugar" Opt_D_dump_ds ds_binds
120 ; doIfSet (dopt Opt_D_dump_ds dflags)
121 (printDump (ppr_ds_rules ds_rules))
123 ; used_names <- mkUsedNames tcg_env
124 ; deps <- mkDependencies tcg_env
126 ; let mod_guts = ModGuts {
128 mg_boot = isHsBoot hsc_src,
129 mg_exports = exports,
131 mg_used_names = used_names,
132 mg_dir_imps = imp_mods imports,
133 mg_rdr_env = rdr_env,
134 mg_fix_env = fix_env,
135 mg_deprecs = deprecs,
138 mg_fam_insts = fam_insts,
139 mg_inst_env = inst_env,
140 mg_fam_inst_env = fam_inst_env,
143 mg_foreign = ds_fords,
144 mg_hpc_info = ds_hpc_info,
145 mg_modBreaks = modBreaks,
146 mg_vect_info = noVectInfo
148 ; return (Just mod_guts)
151 mkAutoScc :: Module -> NameSet -> AutoScc
152 mkAutoScc mod exports
153 | not opt_SccProfilingOn -- No profiling
155 | opt_AutoSccsOnAllToplevs -- Add auto-scc on all top-level things
156 = AddSccs mod (\_ -> True)
157 | opt_AutoSccsOnExportedToplevs -- Only on exported things
158 = AddSccs mod (\id -> idName id `elemNameSet` exports)
163 deSugarExpr :: HscEnv
164 -> Module -> GlobalRdrEnv -> TypeEnv
166 -> IO (Maybe CoreExpr)
167 -- Prints its own errors; returns Nothing if error occurred
169 deSugarExpr hsc_env this_mod rdr_env type_env tc_expr
170 = do { let dflags = hsc_dflags hsc_env
171 ; showPass dflags "Desugar"
174 ; mb_core_expr <- initDs hsc_env this_mod rdr_env type_env $
177 ; case mb_core_expr of {
178 Nothing -> return Nothing ;
182 dumpIfSet_dyn dflags Opt_D_dump_ds "Desugared" (pprCoreExpr expr)
184 ; return (Just expr) } } }
187 -- Set the no-discard flag if either
188 -- a) the Id is exported
189 -- b) it's mentioned in the RHS of an orphan rule
190 -- c) it's in the keep-alive set
192 -- It means that the binding won't be discarded EVEN if the binding
193 -- ends up being trivial (v = w) -- the simplifier would usually just
194 -- substitute w for v throughout, but we don't apply the substitution to
195 -- the rules (maybe we should?), so this substitution would make the rule
198 -- You might wonder why exported Ids aren't already marked as such;
199 -- it's just because the type checker is rather busy already and
200 -- I didn't want to pass in yet another mapping.
202 addExportFlags :: HscTarget -> NameSet -> NameSet -> [(Id, t)] -> [CoreRule]
204 addExportFlags target exports keep_alive prs rules
205 = [(add_export bndr, rhs) | (bndr,rhs) <- prs]
208 | dont_discard bndr = setIdExported bndr
211 orph_rhs_fvs = unionVarSets [ ruleRhsFreeVars rule
213 not (isLocalRule rule) ]
214 -- A non-local rule keeps alive the free vars of its right-hand side.
215 -- (A "non-local" is one whose head function is not locally defined.)
216 -- Local rules are (later, after gentle simplification)
217 -- attached to the Id, and that keeps the rhs free vars alive.
219 dont_discard bndr = is_exported name
220 || name `elemNameSet` keep_alive
221 || bndr `elemVarSet` orph_rhs_fvs
225 -- In interactive mode, we don't want to discard any top-level
226 -- entities at all (eg. do not inline them away during
227 -- simplification), and retain them all in the TypeEnv so they are
228 -- available from the command line.
230 -- isExternalName separates the user-defined top-level names from those
231 -- introduced by the type checker.
232 is_exported :: Name -> Bool
233 is_exported | target == HscInterpreted = isExternalName
234 | otherwise = (`elemNameSet` exports)
236 ppr_ds_rules :: [CoreRule] -> PprStyle -> Doc
237 ppr_ds_rules [] = empty
239 = text "" $$ text "-------------- DESUGARED RULES -----------------" $$
245 %************************************************************************
247 %* Desugaring transformation rules
249 %************************************************************************
252 dsRule :: LRuleDecl Id -> DsM (Maybe CoreRule)
253 dsRule (L loc (HsRule name act vars lhs _tv_lhs rhs _fv_rhs))
255 do { let bndrs = [var | RuleBndr (L _ var) <- vars]
256 ; lhs' <- dsLExpr lhs
257 ; rhs' <- dsLExpr rhs
259 ; case decomposeRuleLhs (occurAnalyseExpr lhs') of {
260 Nothing -> do { warnDs msg; return Nothing } ;
261 Just (fn_id, args) -> do
263 -- Substitute the dict bindings eagerly,
264 -- and take the body apart into a (f args) form
265 { let local_rule = isLocalId fn_id
266 -- NB: isLocalId is False of implicit Ids. This is good becuase
267 -- we don't want to attach rules to the bindings of implicit Ids,
268 -- because they don't show up in the bindings until just before code gen
269 fn_name = idName fn_id
271 rule = Rule { ru_name = name, ru_fn = fn_name, ru_act = act,
272 ru_bndrs = bndrs, ru_args = args, ru_rhs = rhs',
273 ru_rough = roughTopNames args,
274 ru_local = local_rule }
278 msg = hang (ptext SLIT("RULE left-hand side too complicated to desugar; ignored"))