#include "HsVersions.h"
-import CmdLineOpts ( opt_MaxContextReductionDepth, opt_GlasgowExts, opt_WarnTypeDefaults )
import HsSyn ( MonoBinds(..), HsExpr(..), andMonoBinds, andMonoBindList )
import TcHsSyn ( TcExpr, TcId,
TcMonoBinds, TcDictBinds
import TcMonad
import Inst ( lookupInst, lookupSimpleInst, LookupInstResult(..),
- tyVarsOfInst, tyVarsOfInsts,
- isDict, isClassDict, isMethod, isStdClassTyVarDict,
- isMethodFor, notFunDep,
+ tyVarsOfInst,
+ 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, unitLIE, consLIE, plusLIE,
- lieToList, listToLIE
+ lieToList
)
-import TcEnv ( tcGetGlobalTyVars )
-import TcType ( TcType, TcTyVarSet, typeToTcType )
+import TcEnv ( tcGetGlobalTyVars, tcGetInstEnv )
+import InstEnv ( lookupInstEnv, InstLookupResult(..) )
+
+import 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,
+import Type ( Type, 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 ListSetOps ( equivClasses )
+import Util ( zipEqual, mapAccumL )
import List ( partition )
+import Maybe ( fromJust )
import Maybes ( maybeToBool )
+import CmdLineOpts
\end{code}
-> TcTyVarSet -- ``Local'' type variables
-- ASSERT: this tyvar set is already zonked
-> LIE -- Wanted
- -> TcM s (LIE, -- Free
+ -> TcM (LIE, -- Free
TcDictBinds, -- Bindings
LIE) -- Remaining wanteds; no dups
-- 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
-- ASSERT: this tyvar set is already zonked
-> LIE -- Given; constrain only local tyvars
-> LIE -- Wanted
- -> TcM s (LIE, -- Free
+ -> TcM (LIE, -- Free
TcDictBinds) -- Bindings
tcSimplifyAndCheck str local_tvs given_lie wanted_lie
returnTc (mkLIE frees, binds)
where
givens = lieToList given_lie
- -- see comment on wanteds in tcSimplify
- -- JRL nope - it's too early to throw away fundeps here...
- wanteds = {- filter notFunDep -} (lieToList wanted_lie)
+ wanteds = lieToList wanted_lie
given_dicts = filter isClassDict givens
try_me inst
So tcSimplifyToDicts squeezes out all Methods.
\begin{code}
-tcSimplifyToDicts :: LIE -> TcM s (LIE, TcDictBinds)
+tcSimplifyToDicts :: LIE -> TcM (LIE, TcDictBinds)
tcSimplifyToDicts wanted_lie
= reduceContext (text "tcSimplifyToDicts") try_me [] wanteds `thenTc` \ (binds, frees, irreds) ->
ASSERT( null frees )
returnTc (mkLIE irreds, binds)
where
- -- see comment on wanteds in tcSimplify
- -- ZZ waitaminute - doesn't appear that any funDeps should even be here...
- -- wanteds = filter notFunDep (lieToList wanted_lie)
wanteds = lieToList wanted_lie
-- Reduce methods and lits only; stop as soon as we get a dictionary
reduceContext :: SDoc -> (Inst -> WhatToDo)
-> [Inst] -- Given
-> [Inst] -- Wanted
- -> TcM s (TcDictBinds,
+ -> TcM (TcDictBinds,
[Inst], -- Free
[Inst]) -- Irreducible
= -- 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 "----------------------"
]) $
-}
- returnTc (binds, frees, irreds)
+ returnNF_Tc (binds, frees, irreds)
\end{code}
The main context-reduction function is @reduce@. Here's its game plan.
-> (Inst -> WhatToDo)
-> [Inst]
-> RedState s
- -> TcM s (RedState s)
+ -> TcM (RedState s)
\end{code}
@reduce@ is passed
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.
| isDict free = addToFM avails free (Avail (instToId free) NoRhs [])
| otherwise = avails
-addGiven :: Avails s -> Inst -> NF_TcM s (Avails s)
+addGiven :: Avails s -> Inst -> NF_TcM (Avails s)
addGiven avails given
= -- ASSERT( not (given `elemFM` avails) )
-- This assertion isn't necessarily true. It's permitted
addAvail avails wanted avail
= addSuperClasses (addToFM avails wanted avail) wanted
-addSuperClasses :: Avails s -> Inst -> NF_TcM s (Avails s)
+addSuperClasses :: Avails s -> Inst -> NF_TcM (Avails s)
-- Add all the superclasses of the Inst to Avails
-- Invariant: the Inst is already in Avails.
= 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 (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
- -> TcM s ClassContext -- Needed
+tcSimplifyThetas :: ClassContext -- Wanted
+ -> TcM ClassContext -- Needed
-tcSimplifyThetas inst_mapper wanteds
- = reduceSimple inst_mapper [] wanteds `thenNF_Tc` \ irreds ->
+tcSimplifyThetas wanteds
+ = doptsTc Opt_GlasgowExts `thenNF_Tc` \ glaExts ->
+ 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
-- we expect an instance here
-- For Haskell 98, check that all the constraints are of the form C a,
-- where a is a type variable
- bad_guys | opt_GlasgowExts = [ct | ct@(clas,tys) <- irreds,
- isEmptyVarSet (tyVarsOfTypes tys)]
- | otherwise = [ct | ct@(clas,tys) <- irreds,
- not (all isTyVarTy tys)]
+ bad_guys | glaExts = [ct | ct@(clas,tys) <- irreds,
+ isEmptyVarSet (tyVarsOfTypes tys)]
+ | otherwise = [ct | ct@(clas,tys) <- irreds,
+ not (all isTyVarTy tys)]
in
if null bad_guys then
returnTc irreds
\begin{code}
tcSimplifyCheckThetas :: ClassContext -- Given
-> ClassContext -- Wanted
- -> TcM s ()
+ -> TcM ()
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
+ -> NF_TcM 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
+ -> NF_TcM 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)
@LIE@), as well as the @HsBinds@ generated.
\begin{code}
-bindInstsOfLocalFuns :: LIE -> [TcId] -> TcM s (LIE, TcMonoBinds)
+bindInstsOfLocalFuns :: LIE -> [TcId] -> TcM (LIE, TcMonoBinds)
bindInstsOfLocalFuns init_lie local_ids
| null overloaded_ids || null lie_for_here
all the constant and ambiguous Insts.
\begin{code}
-tcSimplifyTop :: LIE -> TcM s TcDictBinds
+tcSimplifyTop :: LIE -> TcM TcDictBinds
tcSimplifyTop wanted_lie
= reduceContext (text "tcSimplTop") try_me [] wanteds `thenTc` \ (binds1, frees, irreds) ->
ASSERT( null frees )
-- Collect together all the bad guys
bad_guys = non_stds ++ concat std_bads
in
-
-- Disambiguate the ones that look feasible
mapTc disambigGroup std_oks `thenTc` \ binds_ambig ->
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
\begin{code}
disambigGroup :: [Inst] -- All standard classes of form (C a)
- -> TcM s TcDictBinds
+ -> TcM TcDictBinds
disambigGroup dicts
| any isNumericClass classes -- Guaranteed all standard classes
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 )
(tidy_env, tidy_dict) = tidyInst emptyTidyEnv dict
warnDefault dicts default_ty
- | not opt_WarnTypeDefaults
- = returnNF_Tc ()
+ = doptsTc Opt_WarnTypeDefaults `thenTc` \ warn_flag ->
+ if warn_flag
+ then mapNF_Tc warn groups `thenNF_Tc_` returnNF_Tc ()
+ else returnNF_Tc ()
- | otherwise
- = warnTc True msg
where
- msg | length dicts > 1
- = (ptext SLIT("Defaulting the following constraint(s) to type") <+> quotes (ppr default_ty))
- $$ pprInstsInFull tidy_dicts
- | otherwise
- = ptext SLIT("Defaulting") <+> quotes (pprInst (head tidy_dicts)) <+>
- ptext SLIT("to type") <+> quotes (ppr default_ty)
-
+ -- Tidy them first
(_, tidy_dicts) = mapAccumL tidyInst emptyTidyEnv dicts
-addRuleLhsErr dict
- = addInstErrTcM (instLoc dict)
- (tidy_env,
- vcat [ptext SLIT("Could not deduce") <+> quotes (pprInst tidy_dict),
- nest 4 (ptext SLIT("LHS of a rule must have no overloading"))])
- where
- (tidy_env, tidy_dict) = tidyInst emptyTidyEnv dict
+ -- Group the dictionaries by source location
+ groups = equivClasses cmp tidy_dicts
+ i1 `cmp` i2 = get_loc i1 `compare` get_loc i2
+ get_loc i = case instLoc i of { (_,loc,_) -> loc }
+
+ warn [dict] = tcAddSrcLoc (get_loc dict) $
+ warnTc True (ptext SLIT("Defaulting") <+> quotes (pprInst dict) <+>
+ ptext SLIT("to type") <+> quotes (ppr default_ty))
+
+ warn dicts = tcAddSrcLoc (get_loc (head dicts)) $
+ warnTc True (vcat [ptext SLIT("Defaulting the following constraint(s) to type") <+> quotes (ppr default_ty),
+ pprInstsInFull dicts])
addTopIPErr dict
= addInstErrTcM (instLoc dict)
where
(tidy_env, tidy_dict) = tidyInst emptyTidyEnv dict
+-- The error message when we don't find a suitable instance
+-- is complicated by the fact that sometimes this is because
+-- there is no instance, and sometimes it's because there are
+-- too many instances (overlap). See the comments in TcEnv.lhs
+-- with the InstEnv stuff.
addNoInstanceErr str givens dict
- = addInstErrTcM (instLoc dict)
- (tidy_env,
- sep [ptext SLIT("Could not deduce") <+> quotes (pprInst tidy_dict),
- nest 4 $ ptext SLIT("from the context:") <+> pprInsts tidy_givens]
- $$
- 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 [sep [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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