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 CmdLineOpts ( DynFlag(..), DynFlags(..), dopt, opt_SccProfilingOn )
12 import HscTypes ( ModGuts(..), ModGuts, HscEnv(..), GhciMode(..),
13 Dependencies(..), TypeEnv, IsBootInterface, unQualInScope )
14 import HsSyn ( RuleDecl(..), RuleBndr(..), HsExpr(..), LHsExpr,
15 HsBindGroup(..), LRuleDecl, HsBind(..) )
16 import TcRnTypes ( TcGblEnv(..), ImportAvails(..) )
17 import MkIface ( mkUsageInfo )
18 import Id ( Id, setIdLocalExported, idName, idIsFrom, isLocalId )
19 import Name ( Name, isExternalName )
21 import PprCore ( pprIdRules, pprCoreExpr )
22 import Subst ( SubstResult(..), substExpr, mkSubst, extendIdSubstList )
24 import DsExpr ( dsLExpr )
25 import DsBinds ( dsHsBinds, 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 )
31 import RdrName ( GlobalRdrEnv )
35 import Bag ( Bag, isEmptyBag, mapBag, emptyBag, bagToList )
36 import CoreLint ( showPass, endPass )
37 import CoreFVs ( ruleRhsFreeVars )
38 import Packages ( PackageState(thPackageId) )
39 import ErrUtils ( doIfSet, dumpIfSet_dyn, pprBagOfWarnings,
40 mkWarnMsg, errorsFound, WarnMsg )
41 import ListSetOps ( insertList )
43 import UniqSupply ( mkSplitUniqSupply )
44 import SrcLoc ( Located(..), SrcSpan, unLoc )
45 import DATA_IOREF ( readIORef )
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,
62 tcg_type_env = type_env,
63 tcg_imports = imports,
64 tcg_exports = exports,
66 tcg_inst_uses = dfun_uses_var,
69 tcg_rdr_env = rdr_env,
70 tcg_fix_env = fix_env,
71 tcg_deprecs = deprecs,
76 = do { showPass dflags "Desugar"
78 -- Desugar the program
79 ; ((all_prs, ds_rules, ds_fords), warns)
80 <- initDs hsc_env mod rdr_env type_env $ do
81 { core_prs <- dsHsBinds auto_scc binds []
82 ; (ds_fords, foreign_prs) <- dsForeigns fords
83 ; let all_prs = foreign_prs ++ core_prs
84 local_bndrs = mkVarSet (map fst all_prs)
85 ; ds_rules <- mappM (dsRule mod local_bndrs) rules
86 ; return (all_prs, 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 | Just 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 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_exports = exports,
152 mg_dir_imps = [m | (m,_,_) <- moduleEnvElts dir_imp_mods],
153 mg_rdr_env = rdr_env,
154 mg_fix_env = fix_env,
155 mg_deprecs = deprecs,
160 mg_foreign = ds_fords }
162 ; return (warns, Just mod_guts)
166 dflags = hsc_dflags hsc_env
167 ghci_mode = hsc_mode hsc_env
168 auto_scc | opt_SccProfilingOn = TopLevel
171 deSugarExpr :: HscEnv
172 -> Module -> GlobalRdrEnv -> TypeEnv
175 deSugarExpr hsc_env this_mod rdr_env type_env tc_expr
176 = do { showPass dflags "Desugar"
177 ; us <- mkSplitUniqSupply 'd'
180 ; (core_expr, ds_warns) <- initDs hsc_env this_mod rdr_env type_env $
183 -- Display any warnings
184 -- Note: if -Werror is used, we don't signal an error here.
185 ; doIfSet (not (isEmptyBag ds_warns))
186 (printErrs (pprBagOfWarnings ds_warns))
189 ; dumpIfSet_dyn dflags Opt_D_dump_ds "Desugared" (pprCoreExpr core_expr)
194 dflags = hsc_dflags hsc_env
198 -- Set the no-discard flag if either
199 -- a) the Id is exported
200 -- b) it's mentioned in the RHS of an orphan rule
201 -- c) it's in the keep-alive set
203 -- It means that the binding won't be discarded EVEN if the binding
204 -- ends up being trivial (v = w) -- the simplifier would usually just
205 -- substitute w for v throughout, but we don't apply the substitution to
206 -- the rules (maybe we should?), so this substitution would make the rule
209 -- You might wonder why exported Ids aren't already marked as such;
210 -- it's just because the type checker is rather busy already and
211 -- I didn't want to pass in yet another mapping.
213 addExportFlags ghci_mode exports keep_alive prs rules
214 = [(add_export bndr, rhs) | (bndr,rhs) <- prs]
217 | isLocalId bndr && dont_discard bndr = setIdLocalExported bndr
218 -- The isLocalId check is to avoid fiddling with
219 -- locally-defined Ids like data cons and class ops
220 -- which are "born" as GlobalIds
223 orph_rhs_fvs = unionVarSets [ ruleRhsFreeVars rule
224 | IdCoreRule _ is_orphan_rule rule <- rules,
226 -- An orphan rule keeps alive the free vars of its right-hand side.
227 -- Non-orphan 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 IdCoreRule
263 dsRule mod in_scope (L loc (HsRule name act vars lhs rhs))
265 ds_lhs all_vars lhs `thenDs` \ (fn, args) ->
266 dsLExpr rhs `thenDs` \ core_rhs ->
267 returnDs (IdCoreRule fn (is_orphan fn) (Rule name act tpl_vars args core_rhs))
269 tpl_vars = [var | RuleBndr (L _ var) <- vars]
270 all_vars = mkInScopeSet (extendVarSetList in_scope tpl_vars)
271 is_orphan id = not (idIsFrom mod id)
272 -- NB we can't use isLocalId in the orphan test,
273 -- because isLocalId isn't true of class methods
279 (HsLet [HsBindGroup dict_binds _ _] body) -> (dict_binds, body)
280 other -> (emptyBag, lhs)
282 mappM ds_dict_bind (bagToList dict_binds) `thenDs` \ dict_binds' ->
283 dsLExpr body `thenDs` \ body' ->
285 -- Substitute the dict bindings eagerly,
286 -- and take the body apart into a (f args) form
288 subst = extendIdSubstList (mkSubst all_vars) pairs
289 pairs = [(id, ContEx subst rhs) | (id,rhs) <- dict_binds']
290 -- Note recursion here... substitution won't terminate
291 -- if there is genuine recursion... which there isn't
292 body'' = substExpr subst body'
295 -- Now unpack the resulting body
297 pair = case collectArgs body'' of
298 (Var fn, args) -> (fn, args)
299 other -> pprPanic "dsRule" (ppr lhs)
303 ds_dict_bind (L _ (VarBind id rhs)) =
304 dsLExpr rhs `thenDs` \ rhs' ->