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(..), ModGuts, HscEnv(..),
15 Dependencies(..), TypeEnv, IsBootInterface )
16 import HsSyn ( RuleDecl(..), RuleBndr(..), HsExpr(..), LHsExpr,
17 HsBindGroup(..), LRuleDecl, HsBind(..) )
18 import TcRnTypes ( TcGblEnv(..), ImportAvails(..) )
19 import MkIface ( mkUsageInfo )
20 import Id ( Id, setIdExported, idName )
21 import Name ( Name, isExternalName, nameIsLocalOrFrom, nameOccName )
23 import PprCore ( pprRules, pprCoreExpr )
24 import CoreSubst ( substExpr, mkSubst )
26 import DsExpr ( dsLExpr )
27 import DsBinds ( dsHsBinds, AutoScc(..) )
28 import DsForeign ( dsForeigns )
29 import DsExpr () -- Forces DsExpr to be compiled; DsBinds only
30 -- depends on DsExpr.hi-boot.
31 import Module ( Module, moduleEnvElts, delModuleEnv, moduleFS )
33 import RdrName ( GlobalRdrEnv )
37 import Bag ( Bag, isEmptyBag, emptyBag, bagToList )
38 import Rules ( roughTopNames )
39 import CoreLint ( showPass, endPass )
40 import CoreFVs ( ruleRhsFreeVars, exprsFreeNames )
41 import Packages ( PackageState(thPackageId), PackageIdH(..) )
42 import ErrUtils ( doIfSet, dumpIfSet_dyn, pprBagOfWarnings,
43 errorsFound, WarnMsg )
44 import ListSetOps ( insertList )
46 import UniqSupply ( mkSplitUniqSupply )
47 import SrcLoc ( Located(..), unLoc )
48 import DATA_IOREF ( readIORef )
50 import Util ( sortLe )
53 %************************************************************************
55 %* The main function: deSugar
57 %************************************************************************
60 deSugar :: HscEnv -> TcGblEnv -> IO (Bag WarnMsg, Maybe ModGuts)
61 -- Can modify PCS by faulting in more declarations
64 tcg_env@(TcGblEnv { tcg_mod = mod,
66 tcg_type_env = type_env,
67 tcg_imports = imports,
68 tcg_exports = exports,
70 tcg_inst_uses = dfun_uses_var,
73 tcg_rdr_env = rdr_env,
74 tcg_fix_env = fix_env,
75 tcg_deprecs = deprecs,
80 = do { showPass dflags "Desugar"
82 -- Desugar the program
83 ; ((all_prs, ds_rules, ds_fords), warns)
84 <- initDs hsc_env mod rdr_env type_env $ do
85 { core_prs <- dsHsBinds auto_scc binds []
86 ; (ds_fords, foreign_prs) <- dsForeigns fords
87 ; let all_prs = foreign_prs ++ core_prs
88 local_bndrs = mkVarSet (map fst all_prs)
89 ; ds_rules <- mappM (dsRule mod local_bndrs) rules
90 ; return (all_prs, ds_rules, ds_fords) }
94 -- If warnings are considered errors, leave.
95 ; if errorsFound dflags (warns, emptyBag)
96 then return (warns, Nothing)
99 { -- Add export flags to bindings
100 keep_alive <- readIORef keep_var
101 ; let final_prs = addExportFlags ghci_mode exports keep_alive
103 ds_binds = [Rec final_prs]
104 -- Notice that we put the whole lot in a big Rec, even the foreign binds
105 -- When compiling PrelFloat, which defines data Float = F# Float#
106 -- we want F# to be in scope in the foreign marshalling code!
107 -- You might think it doesn't matter, but the simplifier brings all top-level
108 -- things into the in-scope set before simplifying; so we get no unfolding for F#!
110 -- Lint result if necessary
111 ; endPass dflags "Desugar" Opt_D_dump_ds ds_binds
114 ; doIfSet (dopt Opt_D_dump_ds dflags)
115 (printDump (ppr_ds_rules ds_rules))
117 ; dfun_uses <- readIORef dfun_uses_var -- What dfuns are used
118 ; th_used <- readIORef th_var -- Whether TH is used
119 ; let used_names = allUses dus `unionNameSets` dfun_uses
120 thPackage = thPackageId (pkgState dflags)
121 pkgs | ExtPackage th_id <- thPackage, th_used
122 = insertList th_id (imp_dep_pkgs imports)
124 = imp_dep_pkgs imports
126 dep_mods = moduleEnvElts (delModuleEnv (imp_dep_mods imports) mod)
127 -- M.hi-boot can be in the imp_dep_mods, but we must remove
128 -- it before recording the modules on which this one depends!
129 -- (We want to retain M.hi-boot in imp_dep_mods so that
130 -- loadHiBootInterface can see if M's direct imports depend
131 -- on M.hi-boot, and hence that we should do the hi-boot consistency
134 dir_imp_mods = imp_mods imports
136 ; usages <- mkUsageInfo hsc_env dir_imp_mods dep_mods used_names
139 -- Modules don't compare lexicographically usually,
140 -- but we want them to do so here.
141 le_mod :: Module -> Module -> Bool
142 le_mod m1 m2 = moduleFS m1 <= moduleFS m2
143 le_dep_mod :: (Module, IsBootInterface) -> (Module, IsBootInterface) -> Bool
144 le_dep_mod (m1,_) (m2,_) = m1 `le_mod` m2
146 deps = Deps { dep_mods = sortLe le_dep_mod dep_mods,
147 dep_pkgs = sortLe (<=) pkgs,
148 dep_orphs = sortLe le_mod (imp_orphs imports) }
149 -- sort to get into canonical order
153 mg_boot = isHsBoot hsc_src,
154 mg_exports = exports,
157 mg_dir_imps = [m | (m,_,_) <- moduleEnvElts dir_imp_mods],
158 mg_rdr_env = rdr_env,
159 mg_fix_env = fix_env,
160 mg_deprecs = deprecs,
165 mg_foreign = ds_fords }
167 ; return (warns, Just mod_guts)
171 dflags = hsc_dflags hsc_env
172 ghci_mode = ghcMode (hsc_dflags hsc_env)
173 auto_scc | opt_SccProfilingOn = TopLevel
176 deSugarExpr :: HscEnv
177 -> Module -> GlobalRdrEnv -> TypeEnv
180 deSugarExpr hsc_env this_mod rdr_env type_env tc_expr
181 = do { showPass dflags "Desugar"
182 ; us <- mkSplitUniqSupply 'd'
185 ; (core_expr, ds_warns) <- initDs hsc_env this_mod rdr_env type_env $
188 -- Display any warnings
189 -- Note: if -Werror is used, we don't signal an error here.
190 ; doIfSet (not (isEmptyBag ds_warns))
191 (printErrs (pprBagOfWarnings ds_warns))
194 ; dumpIfSet_dyn dflags Opt_D_dump_ds "Desugared" (pprCoreExpr core_expr)
199 dflags = hsc_dflags hsc_env
203 -- Set the no-discard flag if either
204 -- a) the Id is exported
205 -- b) it's mentioned in the RHS of an orphan rule
206 -- c) it's in the keep-alive set
208 -- It means that the binding won't be discarded EVEN if the binding
209 -- ends up being trivial (v = w) -- the simplifier would usually just
210 -- substitute w for v throughout, but we don't apply the substitution to
211 -- the rules (maybe we should?), so this substitution would make the rule
214 -- You might wonder why exported Ids aren't already marked as such;
215 -- it's just because the type checker is rather busy already and
216 -- I didn't want to pass in yet another mapping.
218 addExportFlags ghci_mode exports keep_alive prs rules
219 = [(add_export bndr, rhs) | (bndr,rhs) <- prs]
222 | dont_discard bndr = setIdExported bndr
225 orph_rhs_fvs = unionVarSets [ ruleRhsFreeVars rule
227 not (isLocalRule rule) ]
228 -- A non-local rule keeps alive the free vars of its right-hand side.
229 -- (A "non-local" is one whose head function is not locally defined.)
230 -- Local rules are (later, after gentle simplification)
231 -- attached to the Id, and that keeps the rhs free vars alive.
233 dont_discard bndr = is_exported name
234 || name `elemNameSet` keep_alive
235 || bndr `elemVarSet` orph_rhs_fvs
239 -- In interactive mode, we don't want to discard any top-level
240 -- entities at all (eg. do not inline them away during
241 -- simplification), and retain them all in the TypeEnv so they are
242 -- available from the command line.
244 -- isExternalName separates the user-defined top-level names from those
245 -- introduced by the type checker.
246 is_exported :: Name -> Bool
247 is_exported | ghci_mode == Interactive = isExternalName
248 | otherwise = (`elemNameSet` exports)
250 ppr_ds_rules [] = empty
252 = text "" $$ text "-------------- DESUGARED RULES -----------------" $$
258 %************************************************************************
260 %* Desugaring transformation rules
262 %************************************************************************
265 dsRule :: Module -> IdSet -> LRuleDecl Id -> DsM CoreRule
266 dsRule mod in_scope (L loc (HsRule name act vars lhs rhs))
268 do { let (dict_binds, body)
270 (HsLet [HsBindGroup dbs _ _] body) -> (dbs, body)
271 other -> (emptyBag, lhs)
273 ds_dict_bind (L _ (VarBind id rhs))
274 = do { rhs' <- dsLExpr rhs ; returnDs (id,rhs') }
276 ; dict_binds' <- mappM ds_dict_bind (bagToList dict_binds)
277 ; body' <- dsLExpr body
278 ; rhs' <- dsLExpr rhs
280 -- Substitute the dict bindings eagerly,
281 -- and take the body apart into a (f args) form
282 ; let bndrs = [var | RuleBndr (L _ var) <- vars]
283 in_scope' = mkInScopeSet (extendVarSetList in_scope bndrs)
284 subst = mkSubst in_scope' emptyVarEnv (mkVarEnv id_pairs)
285 id_pairs = [(id, substExpr subst rhs) | (id,rhs) <- dict_binds']
286 -- Note recursion here... substitution won't terminate
287 -- if there is genuine recursion... which there isn't
289 body'' = substExpr subst body'
291 (fn, args) = case collectArgs body'' of
292 (Var fn_id, args) -> (idName fn_id, args)
293 other -> pprPanic "dsRule" (ppr lhs)
295 local_rule = nameIsLocalOrFrom mod fn
296 -- NB we can't use isLocalId in the orphan test,
297 -- because isLocalId isn't true of class methods
298 lhs_names = fn : nameSetToList (exprsFreeNames args)
299 -- No need to delete bndrs, because
300 -- exprsFreeNams finds only External names
301 orph = case filter (nameIsLocalOrFrom mod) lhs_names of
302 (n:ns) -> Just (nameOccName n)
305 ; return (Rule { ru_name = name, ru_fn = fn, ru_act = act,
306 ru_bndrs = bndrs, ru_args = args, ru_rhs = rhs',
307 ru_rough = roughTopNames args,
308 ru_local = local_rule, ru_orph = orph })