2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[Desugar]{@deSugar@: the main function}
7 module Desugar ( deSugar, deSugarExpr ) where
9 #include "HsVersions.h"
11 import DynFlags ( DynFlag(..), DynFlags(..), dopt, GhcMode(..) )
12 import StaticFlags ( opt_SccProfilingOn )
13 import DriverPhases ( isHsBoot )
14 import HscTypes ( ModGuts(..), HscEnv(..),
15 Dependencies(..), TypeEnv, IsBootInterface )
16 import HsSyn ( RuleDecl(..), RuleBndr(..), LHsExpr, LRuleDecl )
17 import TcRnTypes ( TcGblEnv(..), ImportAvails(..) )
18 import MkIface ( mkUsageInfo )
19 import Id ( Id, setIdExported, idName )
20 import Name ( Name, isExternalName, nameIsLocalOrFrom, nameOccName )
22 import PprCore ( pprRules, pprCoreExpr )
24 import DsExpr ( dsLExpr )
25 import DsBinds ( dsTopLHsBinds, decomposeRuleLhs, AutoScc(..) )
26 import DsForeign ( dsForeigns )
27 import DsExpr () -- Forces DsExpr to be compiled; DsBinds only
28 -- depends on DsExpr.hi-boot.
29 import Module ( Module, moduleEnvElts, delModuleEnv, moduleFS )
30 import RdrName ( GlobalRdrEnv )
33 import Bag ( Bag, isEmptyBag, emptyBag )
34 import Rules ( roughTopNames )
35 import CoreLint ( showPass, endPass )
36 import CoreFVs ( ruleRhsFreeVars, exprsFreeNames )
37 import Packages ( PackageState(thPackageId), PackageIdH(..) )
38 import ErrUtils ( doIfSet, dumpIfSet_dyn, pprBagOfWarnings,
39 errorsFound, WarnMsg )
40 import ListSetOps ( insertList )
42 import UniqSupply ( mkSplitUniqSupply )
43 import SrcLoc ( Located(..) )
44 import DATA_IOREF ( readIORef )
45 import Maybes ( catMaybes )
47 import Util ( sortLe )
50 %************************************************************************
52 %* The main function: deSugar
54 %************************************************************************
57 deSugar :: HscEnv -> TcGblEnv -> IO (Bag WarnMsg, Maybe ModGuts)
58 -- 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_home_mods = home_mods,
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_deprecs = deprecs,
78 = do { showPass dflags "Desugar"
80 -- Desugar the program
81 ; ((all_prs, ds_rules, ds_fords), warns)
82 <- initDs hsc_env mod rdr_env type_env $ do
83 { core_prs <- dsTopLHsBinds auto_scc binds
84 ; (ds_fords, foreign_prs) <- dsForeigns fords
85 ; let all_prs = foreign_prs ++ core_prs
86 local_bndrs = mkVarSet (map fst all_prs)
87 ; ds_rules <- mappM (dsRule mod local_bndrs) rules
88 ; return (all_prs, catMaybes ds_rules, ds_fords) }
90 -- If warnings are considered errors, leave.
91 ; if errorsFound dflags (warns, emptyBag)
92 then return (warns, Nothing)
95 { -- Add export flags to bindings
96 keep_alive <- readIORef keep_var
97 ; let final_prs = addExportFlags ghci_mode exports keep_alive
99 ds_binds = [Rec final_prs]
100 -- Notice that we put the whole lot in a big Rec, even the foreign binds
101 -- When compiling PrelFloat, which defines data Float = F# Float#
102 -- we want F# to be in scope in the foreign marshalling code!
103 -- You might think it doesn't matter, but the simplifier brings all top-level
104 -- things into the in-scope set before simplifying; so we get no unfolding for F#!
106 -- Lint result if necessary
107 ; endPass dflags "Desugar" Opt_D_dump_ds ds_binds
110 ; doIfSet (dopt Opt_D_dump_ds dflags)
111 (printDump (ppr_ds_rules ds_rules))
113 ; dfun_uses <- readIORef dfun_uses_var -- What dfuns are used
114 ; th_used <- readIORef th_var -- Whether TH is used
115 ; let used_names = allUses dus `unionNameSets` dfun_uses
116 thPackage = thPackageId (pkgState dflags)
117 pkgs | ExtPackage th_id <- thPackage, th_used
118 = insertList th_id (imp_dep_pkgs imports)
120 = imp_dep_pkgs imports
122 dep_mods = moduleEnvElts (delModuleEnv (imp_dep_mods imports) mod)
123 -- M.hi-boot can be in the imp_dep_mods, but we must remove
124 -- it before recording the modules on which this one depends!
125 -- (We want to retain M.hi-boot in imp_dep_mods so that
126 -- loadHiBootInterface can see if M's direct imports depend
127 -- on M.hi-boot, and hence that we should do the hi-boot consistency
130 dir_imp_mods = imp_mods imports
132 ; usages <- mkUsageInfo hsc_env home_mods dir_imp_mods dep_mods used_names
135 -- Modules don't compare lexicographically usually,
136 -- but we want them to do so here.
137 le_mod :: Module -> Module -> Bool
138 le_mod m1 m2 = moduleFS m1 <= moduleFS m2
139 le_dep_mod :: (Module, IsBootInterface) -> (Module, IsBootInterface) -> Bool
140 le_dep_mod (m1,_) (m2,_) = m1 `le_mod` m2
142 deps = Deps { dep_mods = sortLe le_dep_mod dep_mods,
143 dep_pkgs = sortLe (<=) pkgs,
144 dep_orphs = sortLe le_mod (imp_orphs imports) }
145 -- sort to get into canonical order
149 mg_boot = isHsBoot hsc_src,
150 mg_exports = exports,
152 mg_home_mods = home_mods,
154 mg_dir_imps = [m | (m,_,_) <- moduleEnvElts dir_imp_mods],
155 mg_rdr_env = rdr_env,
156 mg_fix_env = fix_env,
157 mg_deprecs = deprecs,
162 mg_foreign = ds_fords }
164 ; return (warns, Just mod_guts)
168 dflags = hsc_dflags hsc_env
169 ghci_mode = ghcMode (hsc_dflags hsc_env)
170 auto_scc | opt_SccProfilingOn = TopLevel
173 deSugarExpr :: HscEnv
174 -> Module -> GlobalRdrEnv -> TypeEnv
177 deSugarExpr hsc_env this_mod rdr_env type_env tc_expr
178 = do { showPass dflags "Desugar"
179 ; us <- mkSplitUniqSupply 'd'
182 ; (core_expr, ds_warns) <- initDs hsc_env this_mod rdr_env type_env $
185 -- Display any warnings
186 -- Note: if -Werror is used, we don't signal an error here.
187 ; doIfSet (not (isEmptyBag ds_warns))
188 (printErrs (pprBagOfWarnings ds_warns))
191 ; dumpIfSet_dyn dflags Opt_D_dump_ds "Desugared" (pprCoreExpr core_expr)
196 dflags = hsc_dflags hsc_env
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 ghci_mode 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 | ghci_mode == Interactive = 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 rhs))
265 do { let bndrs = [var | RuleBndr (L _ var) <- vars]
266 ; lhs' <- dsLExpr lhs
267 ; rhs' <- dsLExpr rhs
269 ; case decomposeRuleLhs bndrs lhs' of {
270 Nothing -> do { dsWarn msg; return Nothing } ;
271 Just (bndrs', 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 = nameIsLocalOrFrom mod fn_name
276 -- NB we can't use isLocalId in the orphan test,
277 -- because isLocalId isn't true of class methods
278 fn_name = idName fn_id
279 lhs_names = fn_name : nameSetToList (exprsFreeNames args)
280 -- No need to delete bndrs, because
281 -- exprsFreeNames finds only External names
282 orph = case filter (nameIsLocalOrFrom mod) lhs_names of
283 (n:ns) -> Just (nameOccName n)
286 rule = Rule { ru_name = name, ru_fn = fn_name, ru_act = act,
287 ru_bndrs = bndrs', ru_args = args, ru_rhs = rhs',
288 ru_rough = roughTopNames args,
289 ru_local = local_rule, ru_orph = orph }
293 msg = hang (ptext SLIT("RULE left-hand side too complicated to desugar; ignored"))