%
% (c) The University of Glasgow 2006
% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
The Desugarer: turning HsSyn into Core.
\begin{code}
module Desugar ( deSugar, deSugarExpr ) where
import DynFlags
import StaticFlags
import HscTypes
import HsSyn
import TcRnTypes
import MkIface
import Id
import Name
import CoreSyn
import CoreSubst
import PprCore
import DsMonad
import DsExpr
import DsBinds
import DsForeign
import DsExpr ()
import Module
import RdrName
import NameSet
import NameEnv
import Rules
import CoreMonad ( endPass, CoreToDo(..) )
import ErrUtils
import Outputable
import SrcLoc
import Coverage
import Util
import MonadUtils
import OrdList
import Data.List
import Data.IORef
\end{code}
%************************************************************************
%* *
%* The main function: deSugar
%* *
%************************************************************************
\begin{code}
deSugar :: HscEnv -> ModLocation -> TcGblEnv -> IO (Messages, Maybe ModGuts)
deSugar hsc_env
mod_loc
tcg_env@(TcGblEnv { tcg_mod = mod,
tcg_src = hsc_src,
tcg_type_env = type_env,
tcg_imports = imports,
tcg_exports = exports,
tcg_keep = keep_var,
tcg_th_splice_used = tc_splice_used,
tcg_rdr_env = rdr_env,
tcg_fix_env = fix_env,
tcg_inst_env = inst_env,
tcg_fam_inst_env = fam_inst_env,
tcg_warns = warns,
tcg_anns = anns,
tcg_binds = binds,
tcg_imp_specs = imp_specs,
tcg_ev_binds = ev_binds,
tcg_fords = fords,
tcg_rules = rules,
tcg_vects = vects,
tcg_insts = insts,
tcg_fam_insts = fam_insts,
tcg_hpc = other_hpc_info })
= do { let dflags = hsc_dflags hsc_env
; showPass dflags "Desugar"
; let export_set = availsToNameSet exports
; let auto_scc = mkAutoScc dflags mod export_set
; let target = hscTarget dflags
; let hpcInfo = emptyHpcInfo other_hpc_info
; (msgs, mb_res)
<- case target of
HscNothing ->
return (emptyMessages,
Just ([], nilOL, [], [], NoStubs, hpcInfo, emptyModBreaks))
_ -> do
(binds_cvr,ds_hpc_info, modBreaks)
<- if (opt_Hpc
|| target == HscInterpreted)
&& (not (isHsBoot hsc_src))
then addCoverageTicksToBinds dflags mod mod_loc
(typeEnvTyCons type_env) binds
else return (binds, hpcInfo, emptyModBreaks)
initDs hsc_env mod rdr_env type_env $ do
do { ds_ev_binds <- dsEvBinds ev_binds
; core_prs <- dsTopLHsBinds auto_scc binds_cvr
; (spec_prs, spec_rules) <- dsImpSpecs imp_specs
; (ds_fords, foreign_prs) <- dsForeigns fords
; ds_rules <- mapMaybeM dsRule rules
; ds_vects <- mapM dsVect vects
; let hpc_init
| opt_Hpc = hpcInitCode mod ds_hpc_info
| otherwise = empty
; return ( ds_ev_binds
, foreign_prs `appOL` core_prs `appOL` spec_prs
, spec_rules ++ ds_rules, ds_vects
, ds_fords `appendStubC` hpc_init
, ds_hpc_info, modBreaks) }
; case mb_res of {
Nothing -> return (msgs, Nothing) ;
Just (ds_ev_binds, all_prs, all_rules, vects0, ds_fords, ds_hpc_info, modBreaks) -> do
{
keep_alive <- readIORef keep_var
; let (rules_for_locals, rules_for_imps)
= partition isLocalRule all_rules
final_prs = addExportFlagsAndRules target
export_set keep_alive rules_for_locals (fromOL all_prs)
final_pgm = combineEvBinds ds_ev_binds final_prs
; dumpIfSet_dyn dflags Opt_D_dump_ds "Desugared, before opt" $
(vcat [ pprCoreBindings final_pgm
, pprRules rules_for_imps ])
; (ds_binds, ds_rules_for_imps, ds_vects)
<- simpleOptPgm dflags mod final_pgm rules_for_imps vects0
; endPass dflags CoreDesugar ds_binds ds_rules_for_imps
; let used_names = mkUsedNames tcg_env
; deps <- mkDependencies tcg_env
; used_th <- readIORef tc_splice_used
; let mod_guts = ModGuts {
mg_module = mod,
mg_boot = isHsBoot hsc_src,
mg_exports = exports,
mg_deps = deps,
mg_used_names = used_names,
mg_used_th = used_th,
mg_dir_imps = imp_mods imports,
mg_rdr_env = rdr_env,
mg_fix_env = fix_env,
mg_warns = warns,
mg_anns = anns,
mg_types = type_env,
mg_insts = insts,
mg_fam_insts = fam_insts,
mg_inst_env = inst_env,
mg_fam_inst_env = fam_inst_env,
mg_rules = ds_rules_for_imps,
mg_binds = ds_binds,
mg_foreign = ds_fords,
mg_hpc_info = ds_hpc_info,
mg_modBreaks = modBreaks,
mg_vect_decls = ds_vects,
mg_vect_info = noVectInfo,
mg_trust_pkg = imp_trust_own_pkg imports
}
; return (msgs, Just mod_guts)
}}}
dsImpSpecs :: [LTcSpecPrag] -> DsM (OrdList (Id,CoreExpr), [CoreRule])
dsImpSpecs imp_specs
= do { spec_prs <- mapMaybeM (dsSpec Nothing) imp_specs
; let (spec_binds, spec_rules) = unzip spec_prs
; return (concatOL spec_binds, spec_rules) }
combineEvBinds :: [DsEvBind] -> [(Id,CoreExpr)] -> [CoreBind]
combineEvBinds [] val_prs
= [Rec val_prs]
combineEvBinds (LetEvBind (NonRec b r) : bs) val_prs
| isId b = combineEvBinds bs ((b,r):val_prs)
| otherwise = NonRec b r : combineEvBinds bs val_prs
combineEvBinds (LetEvBind (Rec prs) : bs) val_prs
= combineEvBinds bs (prs ++ val_prs)
combineEvBinds (CaseEvBind x _ _ : _) _
= pprPanic "topEvBindPairs" (ppr x)
\end{code}
Note [Top-level evidence]
~~~~~~~~~~~~~~~~~~~~~~~~~
Top-level evidence bindings may be mutually recursive with the top-level value
bindings, so we must put those in a Rec. But we can't put them *all* in a Rec
because the occurrence analyser doesn't teke account of type/coercion variables
when computing dependencies.
So we pull out the type/coercion variables (which are in dependency order),
and Rec the rest.
\begin{code}
mkAutoScc :: DynFlags -> Module -> NameSet -> AutoScc
mkAutoScc dflags mod exports
| not opt_SccProfilingOn
= NoSccs
| dopt Opt_AutoSccsOnAllToplevs dflags
= AddSccs mod (\id -> not $ isDerivedOccName $ getOccName id)
| dopt Opt_AutoSccsOnExportedToplevs dflags
= AddSccs mod (\id -> idName id `elemNameSet` exports)
| otherwise
= NoSccs
deSugarExpr :: HscEnv
-> Module -> GlobalRdrEnv -> TypeEnv
-> LHsExpr Id
-> IO (Messages, Maybe CoreExpr)
deSugarExpr hsc_env this_mod rdr_env type_env tc_expr = do
let dflags = hsc_dflags hsc_env
showPass dflags "Desugar"
(msgs, mb_core_expr) <- initDs hsc_env this_mod rdr_env type_env $
dsLExpr tc_expr
case mb_core_expr of
Nothing -> return (msgs, Nothing)
Just expr -> do
dumpIfSet_dyn dflags Opt_D_dump_ds "Desugared" (pprCoreExpr expr)
return (msgs, Just expr)
\end{code}
%************************************************************************
%* *
%* Add rules and export flags to binders
%* *
%************************************************************************
\begin{code}
addExportFlagsAndRules
:: HscTarget -> NameSet -> NameSet -> [CoreRule]
-> [(Id, t)] -> [(Id, t)]
addExportFlagsAndRules target exports keep_alive rules prs
= mapFst add_one prs
where
add_one bndr = add_rules name (add_export name bndr)
where
name = idName bndr
add_rules name bndr
| Just rules <- lookupNameEnv rule_base name
= bndr `addIdSpecialisations` rules
| otherwise
= bndr
rule_base = extendRuleBaseList emptyRuleBase rules
add_export name bndr
| dont_discard name = setIdExported bndr
| otherwise = bndr
dont_discard :: Name -> Bool
dont_discard name = is_exported name
|| name `elemNameSet` keep_alive
is_exported :: Name -> Bool
is_exported | target == HscInterpreted = isExternalName
| otherwise = (`elemNameSet` exports)
\end{code}
Note [Adding export flags]
~~~~~~~~~~~~~~~~~~~~~~~~~~
Set the no-discard flag if either
a) the Id is exported
b) it's mentioned in the RHS of an orphan rule
c) it's in the keep-alive set
It means that the binding won't be discarded EVEN if the binding
ends up being trivial (v = w) -- the simplifier would usually just
substitute w for v throughout, but we don't apply the substitution to
the rules (maybe we should?), so this substitution would make the rule
bogus.
You might wonder why exported Ids aren't already marked as such;
it's just because the type checker is rather busy already and
I didn't want to pass in yet another mapping.
Note [Attach rules to local ids]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Find the rules for locally-defined Ids; then we can attach them
to the binders in the top-level bindings
Reason
- It makes the rules easier to look up
- It means that transformation rules and specialisations for
locally defined Ids are handled uniformly
- It keeps alive things that are referred to only from a rule
(the occurrence analyser knows about rules attached to Ids)
- It makes sure that, when we apply a rule, the free vars
of the RHS are more likely to be in scope
- The imported rules are carried in the in-scope set
which is extended on each iteration by the new wave of
local binders; any rules which aren't on the binding will
thereby get dropped
%************************************************************************
%* *
%* Desugaring transformation rules
%* *
%************************************************************************
\begin{code}
dsRule :: LRuleDecl Id -> DsM (Maybe CoreRule)
dsRule (L loc (HsRule name act vars lhs _tv_lhs rhs _fv_rhs))
= putSrcSpanDs loc $
do { let bndrs' = [var | RuleBndr (L _ var) <- vars]
; lhs' <- unsetDOptM Opt_EnableRewriteRules $
unsetWOptM Opt_WarnIdentities $
dsLExpr lhs
; rhs' <- dsLExpr rhs
; case decomposeRuleLhs bndrs' lhs' of {
Left msg -> do { warnDs msg; return Nothing } ;
Right (final_bndrs, fn_id, args) -> do
{ let is_local = isLocalId fn_id
fn_name = idName fn_id
final_rhs = simpleOptExpr rhs'
rule = mkRule False is_local
name act fn_name final_bndrs args final_rhs
; return (Just rule)
} } }
\end{code}
Note [Desugaring RULE left hand sides]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
For the LHS of a RULE we do *not* want to desugar
[x] to build (\cn. x `c` n)
We want to leave explicit lists simply as chains
of cons's. We can achieve that slightly indirectly by
switching off EnableRewriteRules. See DsExpr.dsExplicitList.
That keeps the desugaring of list comprehensions simple too.
Nor do we want to warn of conversion identities on the LHS;
the rule is precisly to optimise them:
{-# RULES "fromRational/id" fromRational = id :: Rational -> Rational #-}
%************************************************************************
%* *
%* Desugaring vectorisation declarations
%* *
%************************************************************************
\begin{code}
dsVect :: LVectDecl Id -> DsM CoreVect
dsVect (L loc (HsVect (L _ v) rhs))
= putSrcSpanDs loc $
do { rhs' <- fmapMaybeM dsLExpr rhs
; return $ Vect v rhs'
}
dsVect (L _loc (HsNoVect (L _ v)))
= return $ NoVect v
\end{code}