module TcSimplify (
tcSimplify, tcSimplifyAndCheck, tcSimplifyToDicts,
tcSimplifyTop, tcSimplifyThetas, tcSimplifyCheckThetas,
- bindInstsOfLocalFuns
+ bindInstsOfLocalFuns, partitionPredsOfLIE
) where
#include "HsVersions.h"
import TcMonad
import Inst ( lookupInst, lookupSimpleInst, LookupInstResult(..),
tyVarsOfInst, tyVarsOfInsts,
- isDict, isClassDict, isStdClassTyVarDict,
- isMethodFor, notFunDep,
+ isDict, isClassDict, isMethod, notFunDep,
+ isStdClassTyVarDict, isMethodFor,
instToId, instBindingRequired, instCanBeGeneralised,
- newDictFromOld,
- getDictClassTys, getIPs,
+ newDictFromOld, newFunDepFromDict,
+ getDictClassTys, getIPs, isTyVarDict,
+ getDictPred_maybe, getMethodTheta_maybe,
instLoc, pprInst, zonkInst, tidyInst, tidyInsts,
Inst, LIE, pprInsts, pprInstsInFull,
- mkLIE, emptyLIE, plusLIE, lieToList
+ mkLIE, emptyLIE, unitLIE, consLIE, plusLIE,
+ lieToList, listToLIE
)
-import TcEnv ( tcGetGlobalTyVars )
-import TcType ( TcType, TcTyVarSet, typeToTcType )
+import TcEnv ( tcGetGlobalTyVars, tcGetInstEnv,
+ InstEnv, lookupInstEnv, InstLookupResult(..)
+ )
+import TcType ( TcType, TcTyVarSet )
import TcUnify ( unifyTauTy )
import Id ( idType )
-import Class ( Class, classBigSig, classInstEnv )
+import Class ( Class, classBigSig )
import PrelInfo ( isNumericClass, isCreturnableClass, isCcallishClass )
import Type ( Type, ThetaType, TauType, ClassContext,
mkTyVarTy, getTyVar,
isTyVarTy, splitSigmaTy, tyVarsOfTypes
)
-import InstEnv ( InstEnv )
import Subst ( mkTopTyVarSubst, substClasses )
import PprType ( pprConstraint )
import TysWiredIn ( unitTy )
import VarSet
import FiniteMap
-import BasicTypes ( TopLevelFlag(..) )
import CmdLineOpts ( opt_GlasgowExts )
import Outputable
import Util
import List ( partition )
+import Maybe ( fromJust )
+import Maybes ( maybeToBool )
\end{code}
LIE) -- Remaining wanteds; no dups
tcSimplify str local_tvs wanted_lie
-{-
+{- this is just an optimization, and interferes with implicit params,
+ disable it for now. same goes for tcSimplifyAndCheck
| isEmptyVarSet local_tvs
= returnTc (wanted_lie, EmptyMonoBinds, emptyLIE)
-- Finished
returnTc (mkLIE frees, binds, mkLIE irreds')
where
- -- the idea behind filtering out the dependencies here is that
- -- they've already served their purpose, and can be reconstructed
- -- at a later point from the retained class predicates.
- -- however, there *is* the possibility that a dependency
- -- out-lives the predicate from which it arose.
- -- I don't have any examples of this, but if they show up,
- -- we'd want to consider the possibility of saving the
- -- dependencies as hidden constraints (i.e. they'd only
- -- show up in interface files) -- or maybe they'd be useful
- -- as first class predicates...
- wanteds = filter notFunDep (lieToList wanted_lie)
+ wanteds = lieToList wanted_lie
try_me inst
-- Does not constrain a local tyvar
-- We're infering (not checking) the type, and
-- the inst constrains a local type variable
- | isDict inst = DontReduce -- Dicts
- | otherwise = ReduceMe AddToIrreds -- Lits and Methods
+ | isClassDict inst = DontReduceUnlessConstant -- Dicts
+ | otherwise = ReduceMe AddToIrreds -- Lits and Methods
\end{code}
@tcSimplifyAndCheck@ is similar to the above, except that it checks
TcDictBinds) -- Bindings
tcSimplifyAndCheck str local_tvs given_lie wanted_lie
+{-
| isEmptyVarSet local_tvs
-- This can happen quite legitimately; for example in
-- instance Num Int where ...
= returnTc (wanted_lie, EmptyMonoBinds)
| otherwise
+-}
= reduceContext str try_me givens wanteds `thenTc` \ (binds, frees, irreds) ->
-- Complain about any irreducible ones
returnTc (mkLIE frees, binds)
where
givens = lieToList given_lie
- -- see comment on wanteds in tcSimplify
- wanteds = filter notFunDep (lieToList wanted_lie)
+ wanteds = lieToList wanted_lie
given_dicts = filter isClassDict givens
try_me inst
-- Does not constrain a local tyvar
| isEmptyVarSet (tyVarsOfInst inst `intersectVarSet` local_tvs)
+ && (not (isMethod inst) || null (getIPs inst))
= Free
-- When checking against a given signature we always reduce
ASSERT( null frees )
returnTc (mkLIE irreds, binds)
where
- -- see comment on wanteds in tcSimplify
- wanteds = filter notFunDep (lieToList wanted_lie)
+ wanteds = lieToList wanted_lie
-- Reduce methods and lits only; stop as soon as we get a dictionary
try_me inst | isDict inst = DontReduce
| otherwise = ReduceMe AddToIrreds
\end{code}
+The following function partitions a LIE by a predicate defined
+over `Pred'icates (an unfortunate overloading of terminology!).
+This means it sometimes has to split up `Methods', in which case
+a binding is generated.
+
+It is used in `with' bindings to extract from the LIE the implicit
+parameters being bound.
+
+\begin{code}
+partitionPredsOfLIE pred lie
+ = foldlTc (partPreds pred) (emptyLIE, emptyLIE, EmptyMonoBinds) insts
+ where insts = lieToList lie
+
+-- warning: the term `pred' is overloaded here!
+partPreds pred (lie1, lie2, binds) inst
+ | maybeToBool maybe_pred
+ = if pred p then
+ returnTc (consLIE inst lie1, lie2, binds)
+ else
+ returnTc (lie1, consLIE inst lie2, binds)
+ where maybe_pred = getDictPred_maybe inst
+ Just p = maybe_pred
+
+-- the assumption is that those satisfying `pred' are being extracted,
+-- so we leave the method untouched when nothing satisfies `pred'
+partPreds pred (lie1, lie2, binds1) inst
+ | maybeToBool maybe_theta
+ = if any pred theta then
+ zonkInst inst `thenTc` \ inst' ->
+ tcSimplifyToDicts (unitLIE inst') `thenTc` \ (lie3, binds2) ->
+ partitionPredsOfLIE pred lie3 `thenTc` \ (lie1', lie2', EmptyMonoBinds) ->
+ returnTc (lie1 `plusLIE` lie1',
+ lie2 `plusLIE` lie2',
+ binds1 `AndMonoBinds` binds2)
+ else
+ returnTc (lie1, consLIE inst lie2, binds1)
+ where maybe_theta = getMethodTheta_maybe inst
+ Just theta = maybe_theta
+
+partPreds pred (lie1, lie2, binds) inst
+ = returnTc (lie1, consLIE inst lie2, binds)
+\end{code}
%************************************************************************
= ReduceMe -- Try to reduce this
NoInstanceAction -- What to do if there's no such instance
- | DontReduce -- Return as irreducible
+ | DontReduce -- Return as irreducible
+
+ | DontReduceUnlessConstant -- Return as irreducible unless it can
+ -- be reduced to a constant in one step
| Free -- Return as free
pprAvails avails = vcat (map pprAvail (eltsFM avails))
-
+
pprAvail (Avail main_id rhs ids)
= ppr main_id <> colon <+> brackets (ppr ids) <+> pprRhs rhs
+instance Outputable Avail where
+ ppr = pprAvail
+
pprRhs NoRhs = text "<no rhs>"
pprRhs (Rhs rhs b) = ppr rhs
pprRhs (PassiveScSel rhs is) = text "passive" <+> ppr rhs
= -- Zonking first
mapNF_Tc zonkInst givens `thenNF_Tc` \ givens ->
mapNF_Tc zonkInst wanteds `thenNF_Tc` \ wanteds ->
+ -- JRL - process fundeps last. We eliminate fundeps by seeing
+ -- what available classes generate them, so we need to process the
+ -- classes first. (would it be useful to make LIEs ordered in the first place?)
+ let (wantedOther, wantedFds) = partition notFunDep wanteds
+ wanteds' = wantedOther ++ wantedFds in
{-
pprTrace "reduceContext" (vcat [
]) $
-}
-- Build the Avail mapping from "givens"
- foldlNF_Tc addGiven emptyFM givens `thenNF_Tc` \ avails ->
+ foldlNF_Tc addGiven emptyFM givens `thenNF_Tc` \ avails ->
-- Do the real work
- reduceList (0,[]) try_me wanteds (avails, [], []) `thenTc` \ (avails, frees, irreds) ->
+ reduceList (0,[]) try_me wanteds' (avails, [], []) `thenNF_Tc` \ (avails, frees, irreds) ->
-- Extract the bindings from avails
let
text "wanted" <+> ppr wanteds,
text "----",
text "avails" <+> pprAvails avails,
+ text "frees" <+> ppr frees,
text "irreds" <+> ppr irreds,
text "----------------------"
]) $
-}
- returnTc (binds, frees, irreds)
+ returnNF_Tc (binds, frees, irreds)
\end{code}
The main context-reduction function is @reduce@. Here's its game plan.
;
- DontReduce -> -- It's irreducible (or at least should not be reduced)
+
+ DontReduce -> add_to_irreds
+ ;
+
+ DontReduceUnlessConstant -> -- It's irreducible (or at least should not be reduced)
-- See if the inst can be reduced to a constant in one step
lookupInst wanted `thenNF_Tc` \ lookup_result ->
case lookup_result of
addWanted avails wanted rhs_expr
= ASSERT( not (wanted `elemFM` avails) )
- returnNF_Tc (addToFM avails wanted avail)
+ addFunDeps (addToFM avails wanted avail) wanted
-- NB: we don't add the thing's superclasses too!
-- Why not? Because addWanted is used when we've successfully used an
-- instance decl to reduce something; e.g.
= returnNF_Tc avails
| otherwise -- It is a dictionary
- = foldlNF_Tc add_sc avails (zipEqual "addSuperClasses" sc_theta' sc_sels)
+ = foldlNF_Tc add_sc avails (zipEqual "addSuperClasses" sc_theta' sc_sels) `thenNF_Tc` \ avails' ->
+ addFunDeps avails' dict
where
(clas, tys) = getDictClassTys dict
-
(tyvars, sc_theta, sc_sels, _) = classBigSig clas
sc_theta' = substClasses (mkTopTyVarSubst tyvars tys) sc_theta
avail = Avail (instToId super_dict)
(PassiveScSel sc_sel_rhs [dict])
[]
+
+addFunDeps :: Avails s -> Inst -> NF_TcM s (Avails s)
+ -- Add in the functional dependencies generated by the inst
+addFunDeps avails inst
+ = newFunDepFromDict inst `thenNF_Tc` \ fdInst_maybe ->
+ case fdInst_maybe of
+ Nothing -> returnNF_Tc avails
+ Just fdInst ->
+ let fdAvail = Avail (instToId (fromJust fdInst_maybe)) NoRhs [] in
+ addAvail avails fdInst fdAvail
\end{code}
%************************************************************************
instance declarations.
\begin{code}
-tcSimplifyThetas :: (Class -> InstEnv) -- How to find the InstEnv
- -> ClassContext -- Wanted
+tcSimplifyThetas :: ClassContext -- Wanted
-> TcM s ClassContext -- Needed
-tcSimplifyThetas inst_mapper wanteds
- = reduceSimple inst_mapper [] wanteds `thenNF_Tc` \ irreds ->
+tcSimplifyThetas wanteds
+ = reduceSimple [] wanteds `thenNF_Tc` \ irreds ->
let
-- For multi-param Haskell, check that the returned dictionaries
-- don't have any of the form (C Int Bool) for which
-> TcM s ()
tcSimplifyCheckThetas givens wanteds
- = reduceSimple classInstEnv givens wanteds `thenNF_Tc` \ irreds ->
+ = reduceSimple givens wanteds `thenNF_Tc` \ irreds ->
if null irreds then
returnTc ()
else
-- True => irreducible
-- False => given, or can be derived from a given or from an irreducible
-reduceSimple :: (Class -> InstEnv)
- -> ClassContext -- Given
+reduceSimple :: ClassContext -- Given
-> ClassContext -- Wanted
-> NF_TcM s ClassContext -- Irreducible
-reduceSimple inst_mapper givens wanteds
- = reduce_simple (0,[]) inst_mapper givens_fm wanteds `thenNF_Tc` \ givens_fm' ->
+reduceSimple givens wanteds
+ = reduce_simple (0,[]) givens_fm wanteds `thenNF_Tc` \ givens_fm' ->
returnNF_Tc [ct | (ct,True) <- fmToList givens_fm']
where
givens_fm = foldl addNonIrred emptyFM givens
reduce_simple :: (Int,ClassContext) -- Stack
- -> (Class -> InstEnv)
-> AvailsSimple
-> ClassContext
-> NF_TcM s AvailsSimple
-reduce_simple (n,stack) inst_mapper avails wanteds
+reduce_simple (n,stack) avails wanteds
= go avails wanteds
where
go avails [] = returnNF_Tc avails
- go avails (w:ws) = reduce_simple_help (n+1,w:stack) inst_mapper avails w `thenNF_Tc` \ avails' ->
+ go avails (w:ws) = reduce_simple_help (n+1,w:stack) avails w `thenNF_Tc` \ avails' ->
go avails' ws
-reduce_simple_help stack inst_mapper givens wanted@(clas,tys)
+reduce_simple_help stack givens wanted@(clas,tys)
| wanted `elemFM` givens
= returnNF_Tc givens
| otherwise
- = lookupSimpleInst (inst_mapper clas) clas tys `thenNF_Tc` \ maybe_theta ->
+ = lookupSimpleInst clas tys `thenNF_Tc` \ maybe_theta ->
case maybe_theta of
Nothing -> returnNF_Tc (addIrred givens wanted)
- Just theta -> reduce_simple stack inst_mapper (addNonIrred givens wanted) theta
+ Just theta -> reduce_simple stack (addNonIrred givens wanted) theta
addIrred :: AvailsSimple -> (Class,[Type]) -> AvailsSimple
addIrred givens ct@(clas,tys)
returnTc (binds1 `andMonoBinds` andMonoBindList binds_ambig)
where
- -- see comment on wanteds in tcSimplify
- wanteds = filter notFunDep (lieToList wanted_lie)
+ wanteds = lieToList wanted_lie
try_me inst = ReduceMe AddToIrreds
d1 `cmp_by_tyvar` d2 = get_tv d1 `compare` get_tv d2
try_default default_tys `thenTc` \ chosen_default_ty ->
-- Bind the type variable and reduce the context, for real this time
- let
- chosen_default_tc_ty = typeToTcType chosen_default_ty -- Tiresome!
- in
- unifyTauTy chosen_default_tc_ty (mkTyVarTy tyvar) `thenTc_`
+ unifyTauTy chosen_default_ty (mkTyVarTy tyvar) `thenTc_`
reduceContext (text "disambig" <+> ppr dicts)
try_me [] dicts `thenTc` \ (binds, frees, ambigs) ->
ASSERT( null frees && null ambigs )
addAmbigErr ambig_tv_fn dict
= addInstErrTcM (instLoc dict)
(tidy_env,
- sep [text "Ambiguous type variable(s)" <+>
- hsep (punctuate comma (map (quotes . ppr) ambig_tvs)),
+ sep [text "Ambiguous type variable(s)" <+> pprQuotedList ambig_tvs,
nest 4 (text "in the constraint" <+> quotes (pprInst tidy_dict))])
where
ambig_tvs = varSetElems (ambig_tv_fn tidy_dict)
where
(tidy_env, tidy_dict) = tidyInst emptyTidyEnv dict
+-- The error message when we don't find a suitable instance
+-- is complicated by the fact that sometimes this is because
+-- there is no instance, and sometimes it's because there are
+-- too many instances (overlap). See the comments in TcEnv.lhs
+-- with the InstEnv stuff.
addNoInstanceErr str givens dict
- = addInstErrTcM (instLoc dict)
- (tidy_env,
- sep [ptext SLIT("Could not deduce") <+> quotes (pprInst tidy_dict),
- nest 4 $ ptext SLIT("from the context:") <+> pprInsts tidy_givens]
- $$
- ptext SLIT("Probable cause:") <+>
- vcat [sep [ptext SLIT("missing") <+> quotes (pprInst tidy_dict),
- ptext SLIT("in") <+> str],
- if isClassDict dict && all_tyvars then empty else
- ptext SLIT("or missing instance declaration for") <+> quotes (pprInst tidy_dict)]
- )
- where
- all_tyvars = all isTyVarTy tys
- (_, tys) = getDictClassTys dict
- (tidy_env, tidy_dict:tidy_givens) = tidyInsts emptyTidyEnv (dict:givens)
+ = tcGetInstEnv `thenNF_Tc` \ inst_env ->
+ let
+ doc = vcat [herald <+> quotes (pprInst tidy_dict),
+ nest 4 $ ptext SLIT("from the context") <+> pprInsts tidy_givens,
+ ambig_doc,
+ ptext SLIT("Probable fix:"),
+ nest 4 fix1,
+ nest 4 fix2]
+
+ herald = ptext SLIT("Could not") <+> unambig_doc <+> ptext SLIT("deduce")
+ unambig_doc | ambig_overlap = ptext SLIT("unambiguously")
+ | otherwise = empty
+
+ ambig_doc
+ | not ambig_overlap = empty
+ | otherwise
+ = vcat [ptext SLIT("The choice of (overlapping) instance declaration"),
+ nest 4 (ptext SLIT("depends on the instantiation of") <+>
+ quotes (pprWithCommas ppr (varSetElems (tyVarsOfInst tidy_dict))))]
+
+ fix1 = sep [ptext SLIT("Add") <+> quotes (pprInst tidy_dict),
+ ptext SLIT("to the") <+> str]
+
+ fix2 | isTyVarDict dict || ambig_overlap
+ = empty
+ | otherwise
+ = ptext SLIT("Or add an instance declaration for") <+> quotes (pprInst tidy_dict)
+
+ (tidy_env, tidy_dict:tidy_givens) = tidyInsts emptyTidyEnv (dict:givens)
+
+ -- Checks for the ambiguous case when we have overlapping instances
+ ambig_overlap | isClassDict dict
+ = case lookupInstEnv inst_env clas tys of
+ NoMatch ambig -> ambig
+ other -> False
+ | otherwise = False
+ where
+ (clas,tys) = getDictClassTys dict
+ in
+ addInstErrTcM (instLoc dict) (tidy_env, doc)
-- Used for the ...Thetas variants; all top level
addNoInstErr (c,ts)
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