2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
6 The Desugarer: turning HsSyn into Core.
10 -- The above warning supression flag is a temporary kludge.
11 -- While working on this module you are encouraged to remove it and fix
12 -- any warnings in the module. See
13 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
16 module Desugar ( deSugar, deSugarExpr ) where
18 #include "HsVersions.h"
35 import DsExpr () -- Forces DsExpr to be compiled; DsBinds only
36 -- depends on DsExpr.hi-boot.
58 %************************************************************************
60 %* The main function: deSugar
62 %************************************************************************
65 deSugar :: HscEnv -> ModLocation -> TcGblEnv -> IO (Maybe ModGuts)
66 -- Can modify PCS by faulting in more declarations
70 tcg_env@(TcGblEnv { tcg_mod = mod,
72 tcg_type_env = type_env,
73 tcg_imports = imports,
74 tcg_exports = exports,
75 tcg_inst_uses = dfun_uses_var,
78 tcg_rdr_env = rdr_env,
79 tcg_fix_env = fix_env,
80 tcg_inst_env = inst_env,
81 tcg_fam_inst_env = fam_inst_env,
82 tcg_deprecs = deprecs,
87 tcg_fam_insts = fam_insts,
88 tcg_hpc = other_hpc_info })
90 = do { let dflags = hsc_dflags hsc_env
91 ; showPass dflags "Desugar"
93 -- Desugar the program
94 ; let export_set = availsToNameSet exports
95 ; let auto_scc = mkAutoScc mod export_set
96 ; let target = hscTarget dflags
97 ; let hpcInfo = emptyHpcInfo other_hpc_info
98 ; mb_res <- case target of
99 HscNothing -> return (Just ([], [], NoStubs, hpcInfo, emptyModBreaks))
100 _ -> do (binds_cvr,ds_hpc_info, modBreaks)
102 || target == HscInterpreted)
103 && (not (isHsBoot hsc_src))
104 then addCoverageTicksToBinds dflags mod mod_loc (typeEnvTyCons type_env) binds
105 else return (binds, hpcInfo, emptyModBreaks)
106 initDs hsc_env mod rdr_env type_env $ do
107 { core_prs <- dsTopLHsBinds auto_scc binds_cvr
108 ; (ds_fords, foreign_prs) <- dsForeigns fords
109 ; let all_prs = foreign_prs ++ core_prs
110 local_bndrs = mkVarSet (map fst all_prs)
111 ; ds_rules <- mappM (dsRule mod local_bndrs) rules
112 ; return (all_prs, catMaybes ds_rules, ds_fords, ds_hpc_info, modBreaks)
115 Nothing -> return Nothing ;
116 Just (all_prs, ds_rules, ds_fords,ds_hpc_info, modBreaks) -> do
118 { -- Add export flags to bindings
119 keep_alive <- readIORef keep_var
120 ; let final_prs = addExportFlags target export_set
121 keep_alive all_prs ds_rules
122 ds_binds = [Rec final_prs]
123 -- Notice that we put the whole lot in a big Rec, even the foreign binds
124 -- When compiling PrelFloat, which defines data Float = F# Float#
125 -- we want F# to be in scope in the foreign marshalling code!
126 -- You might think it doesn't matter, but the simplifier brings all top-level
127 -- things into the in-scope set before simplifying; so we get no unfolding for F#!
129 -- Lint result if necessary
130 ; endPass dflags "Desugar" Opt_D_dump_ds ds_binds
133 ; doIfSet (dopt Opt_D_dump_ds dflags)
134 (printDump (ppr_ds_rules ds_rules))
136 ; used_names <- mkUsedNames tcg_env
137 ; deps <- mkDependencies tcg_env
139 ; let mod_guts = ModGuts {
141 mg_boot = isHsBoot hsc_src,
142 mg_exports = exports,
144 mg_used_names = used_names,
145 mg_dir_imps = imp_mods imports,
146 mg_rdr_env = rdr_env,
147 mg_fix_env = fix_env,
148 mg_deprecs = deprecs,
151 mg_fam_insts = fam_insts,
152 mg_inst_env = inst_env,
153 mg_fam_inst_env = fam_inst_env,
156 mg_foreign = ds_fords,
157 mg_hpc_info = ds_hpc_info,
158 mg_modBreaks = modBreaks,
159 mg_vect_info = noVectInfo
161 ; return (Just mod_guts)
164 mkAutoScc :: Module -> NameSet -> AutoScc
165 mkAutoScc mod exports
166 | not opt_SccProfilingOn -- No profiling
168 | opt_AutoSccsOnAllToplevs -- Add auto-scc on all top-level things
169 = AddSccs mod (\id -> True)
170 | opt_AutoSccsOnExportedToplevs -- Only on exported things
171 = AddSccs mod (\id -> idName id `elemNameSet` exports)
176 deSugarExpr :: HscEnv
177 -> Module -> GlobalRdrEnv -> TypeEnv
179 -> IO (Maybe CoreExpr)
180 -- Prints its own errors; returns Nothing if error occurred
182 deSugarExpr hsc_env this_mod rdr_env type_env tc_expr
183 = do { let dflags = hsc_dflags hsc_env
184 ; showPass dflags "Desugar"
187 ; mb_core_expr <- initDs hsc_env this_mod rdr_env type_env $
190 ; case mb_core_expr of {
191 Nothing -> return Nothing ;
195 dumpIfSet_dyn dflags Opt_D_dump_ds "Desugared" (pprCoreExpr expr)
197 ; return (Just expr) } } }
200 -- Set the no-discard flag if either
201 -- a) the Id is exported
202 -- b) it's mentioned in the RHS of an orphan rule
203 -- c) it's in the keep-alive set
205 -- It means that the binding won't be discarded EVEN if the binding
206 -- ends up being trivial (v = w) -- the simplifier would usually just
207 -- substitute w for v throughout, but we don't apply the substitution to
208 -- the rules (maybe we should?), so this substitution would make the rule
211 -- You might wonder why exported Ids aren't already marked as such;
212 -- it's just because the type checker is rather busy already and
213 -- I didn't want to pass in yet another mapping.
215 addExportFlags target exports keep_alive prs rules
216 = [(add_export bndr, rhs) | (bndr,rhs) <- prs]
219 | dont_discard bndr = setIdExported bndr
222 orph_rhs_fvs = unionVarSets [ ruleRhsFreeVars rule
224 not (isLocalRule rule) ]
225 -- A non-local rule keeps alive the free vars of its right-hand side.
226 -- (A "non-local" is one whose head function is not locally defined.)
227 -- Local rules are (later, after gentle simplification)
228 -- attached to the Id, and that keeps the rhs free vars alive.
230 dont_discard bndr = is_exported name
231 || name `elemNameSet` keep_alive
232 || bndr `elemVarSet` orph_rhs_fvs
236 -- In interactive mode, we don't want to discard any top-level
237 -- entities at all (eg. do not inline them away during
238 -- simplification), and retain them all in the TypeEnv so they are
239 -- available from the command line.
241 -- isExternalName separates the user-defined top-level names from those
242 -- introduced by the type checker.
243 is_exported :: Name -> Bool
244 is_exported | target == HscInterpreted = isExternalName
245 | otherwise = (`elemNameSet` exports)
247 ppr_ds_rules [] = empty
249 = text "" $$ text "-------------- DESUGARED RULES -----------------" $$
255 %************************************************************************
257 %* Desugaring transformation rules
259 %************************************************************************
262 dsRule :: Module -> IdSet -> LRuleDecl Id -> DsM (Maybe CoreRule)
263 dsRule mod in_scope (L loc (HsRule name act vars lhs tv_lhs rhs fv_rhs))
265 do { let bndrs = [var | RuleBndr (L _ var) <- vars]
266 ; lhs' <- dsLExpr lhs
267 ; rhs' <- dsLExpr rhs
269 ; case decomposeRuleLhs (occurAnalyseExpr lhs') of {
270 Nothing -> do { warnDs msg; return Nothing } ;
271 Just (fn_id, args) -> do
273 -- Substitute the dict bindings eagerly,
274 -- and take the body apart into a (f args) form
275 { let local_rule = isLocalId fn_id
276 -- NB: isLocalId is False of implicit Ids. This is good becuase
277 -- we don't want to attach rules to the bindings of implicit Ids,
278 -- because they don't show up in the bindings until just before code gen
279 fn_name = idName fn_id
281 rule = Rule { ru_name = name, ru_fn = fn_name, ru_act = act,
282 ru_bndrs = bndrs, ru_args = args, ru_rhs = rhs',
283 ru_rough = roughTopNames args,
284 ru_local = local_rule }
288 msg = hang (ptext SLIT("RULE left-hand side too complicated to desugar; ignored"))