TcSimplify
\begin{code}
-{-# OPTIONS -w #-}
--- The above warning supression flag is a temporary kludge.
--- While working on this module you are encouraged to remove it and fix
--- any warnings in the module. See
--- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
--- for details
-
module TcSimplify (
tcSimplifyInfer, tcSimplifyInferCheck,
tcSimplifyCheck, tcSimplifyRestricted,
import HsSyn
import TcRnMonad
+import TcHsSyn ( hsLPatType )
import Inst
import TcEnv
import InstEnv
-import TcGadt
import TcType
import TcMType
import TcIface
import TcTyFuns
-import TypeRep
+import DsUtils -- Big-tuple functions
import Var
import Name
import NameSet
import BasicTypes
import VarSet
import VarEnv
-import Module
import FiniteMap
import Bag
import Outputable
import Maybes
import ListSetOps
import Util
-import UniqSet
import SrcLoc
import DynFlags
+import FastString
+import Control.Monad
import Data.List
\end{code}
Here is a more complicated example:
-| > class Foo a b | a->b
-| >
-| > class Bar a b | a->b
-| >
-| > data Obj = Obj
-| >
-| > instance Bar Obj Obj
-| >
-| > instance (Bar a b) => Foo a b
-| >
-| > foo:: (Foo a b) => a -> String
-| > foo _ = "works"
-| >
-| > runFoo:: (forall a b. (Foo a b) => a -> w) -> w
-| > runFoo f = f Obj
-|
-| *Test> runFoo foo
-|
-| <interactive>:1:
-| Could not deduce (Bar a b) from the context (Foo a b)
-| arising from use of `foo' at <interactive>:1
-| Probable fix:
-| Add (Bar a b) to the expected type of an expression
-| In the first argument of `runFoo', namely `foo'
-| In the definition of `it': it = runFoo foo
-|
-| Why all of the sudden does GHC need the constraint Bar a b? The
-| function foo didn't ask for that...
+@
+ > class Foo a b | a->b
+ >
+ > class Bar a b | a->b
+ >
+ > data Obj = Obj
+ >
+ > instance Bar Obj Obj
+ >
+ > instance (Bar a b) => Foo a b
+ >
+ > foo:: (Foo a b) => a -> String
+ > foo _ = "works"
+ >
+ > runFoo:: (forall a b. (Foo a b) => a -> w) -> w
+ > runFoo f = f Obj
+
+ *Test> runFoo foo
+
+ <interactive>:1:
+ Could not deduce (Bar a b) from the context (Foo a b)
+ arising from use of `foo' at <interactive>:1
+ Probable fix:
+ Add (Bar a b) to the expected type of an expression
+ In the first argument of `runFoo', namely `foo'
+ In the definition of `it': it = runFoo foo
+
+ Why all of the sudden does GHC need the constraint Bar a b? The
+ function foo didn't ask for that...
+@
The trouble is that to type (runFoo foo), GHC has to solve the problem:
&& isFreeWrtIPs ips inst
-}
+isFreeWrtTyVars :: VarSet -> Inst -> Bool
isFreeWrtTyVars qtvs inst = tyVarsOfInst inst `disjointVarSet` qtvs
+isFreeWrtIPs :: NameSet -> Inst -> Bool
isFreeWrtIPs ips inst = not (any (`elemNameSet` ips) (ipNamesOfInst inst))
\end{code}
-----------------------------------------------------------
-- tcSimplifyCheckPat is used for existential pattern match
tcSimplifyCheckPat :: InstLoc
- -> [CoVar]
-> [TcTyVar] -- Quantify over these
-> [Inst] -- Given
-> [Inst] -- Wanted
-> TcM TcDictBinds -- Bindings
-tcSimplifyCheckPat loc co_vars qtvs givens wanteds
+tcSimplifyCheckPat loc qtvs givens wanteds
= ASSERT( all isTcTyVar qtvs && all isSkolemTyVar qtvs )
do { traceTc (text "tcSimplifyCheckPat")
; (irreds, binds) <- gentleCheckLoop loc givens wanteds
- ; implic_bind <- bindIrredsR loc qtvs co_vars emptyRefinement
- givens irreds
+ ; implic_bind <- bindIrredsR loc qtvs givens irreds
; return (binds `unionBags` implic_bind) }
-----------------------------------------------------------
-> [Inst] -> [Inst]
-> TcM TcDictBinds
bindIrreds loc qtvs givens irreds
- = bindIrredsR loc qtvs [] emptyRefinement givens irreds
+ = bindIrredsR loc qtvs givens irreds
-bindIrredsR :: InstLoc -> [TcTyVar] -> [CoVar]
- -> Refinement -> [Inst] -> [Inst]
- -> TcM TcDictBinds
+bindIrredsR :: InstLoc -> [TcTyVar] -> [Inst] -> [Inst] -> TcM TcDictBinds
-- Make a binding that binds 'irreds', by generating an implication
-- constraint for them, *and* throwing the constraint into the LIE
-bindIrredsR loc qtvs co_vars reft givens irreds
+bindIrredsR loc qtvs givens irreds
| null irreds
= return emptyBag
| otherwise
-- There should be no implicadtion constraints
-- See Note [Pruning the givens in an implication constraint]
- -- If there are no 'givens' *and* the refinement is empty
- -- (the refinement is like more givens), then it's safe to
+ -- If there are no 'givens', then it's safe to
-- partition the 'wanteds' by their qtvs, thereby trimming irreds
-- See Note [Freeness and implications]
- ; irreds' <- if null givens' && isEmptyRefinement reft
+ ; irreds' <- if null givens'
then do
{ let qtv_set = mkVarSet qtvs
(frees, real_irreds) = partition (isFreeWrtTyVars qtv_set) irreds
; return real_irreds }
else return irreds
- ; let all_tvs = qtvs ++ co_vars -- Abstract over all these
- ; (implics, bind) <- makeImplicationBind loc all_tvs reft givens' irreds'
+ ; (implics, bind) <- makeImplicationBind loc qtvs givens' irreds'
-- This call does the real work
-- If irreds' is empty, it does something sensible
; extendLIEs implics
; return bind }
-makeImplicationBind :: InstLoc -> [TcTyVar] -> Refinement
+makeImplicationBind :: InstLoc -> [TcTyVar]
-> [Inst] -> [Inst]
-> TcM ([Inst], TcDictBinds)
-- Make a binding that binds 'irreds', by generating an implication
-- qtvs includes coercion variables
--
-- This binding must line up the 'rhs' in reduceImplication
-makeImplicationBind loc all_tvs reft
+makeImplicationBind loc all_tvs
givens -- Guaranteed all Dicts
-- or EqInsts
irreds
-- 'givens' must be a simple CoVar. This MUST be cleaned up.
; let name = mkInternalName uniq (mkVarOcc "ic") span
- implic_inst = ImplicInst { tci_name = name, tci_reft = reft,
+ implic_inst = ImplicInst { tci_name = name,
tci_tyvars = all_tvs,
tci_given = (eq_givens ++ dict_givens),
tci_wanted = irreds, tci_loc = loc }
; let -- only create binder for dict_irreds
- (eq_irreds, dict_irreds) = partition isEqInst irreds
- n_dict_irreds = length dict_irreds
+ (_, dict_irreds) = partition isEqInst irreds
dict_irred_ids = map instToId dict_irreds
- tup_ty = mkTupleTy Boxed n_dict_irreds (map idType dict_irred_ids)
- pat = TuplePat (map nlVarPat dict_irred_ids) Boxed tup_ty
+ lpat = mkBigLHsPatTup (map (L span . VarPat) dict_irred_ids)
rhs = L span (mkHsWrap co (HsVar (instToId implic_inst)))
co = mkWpApps (map instToId dict_givens)
<.> mkWpTyApps eq_tyvar_cos
<.> mkWpTyApps (mkTyVarTys all_tvs)
bind | [dict_irred_id] <- dict_irred_ids = VarBind dict_irred_id rhs
- | otherwise = PatBind { pat_lhs = L span pat,
+ | otherwise = PatBind { pat_lhs = lpat,
pat_rhs = unguardedGRHSs rhs,
- pat_rhs_ty = tup_ty,
+ pat_rhs_ty = hsLPatType lpat,
bind_fvs = placeHolderNames }
; traceTc $ text "makeImplicationBind" <+> ppr implic_inst
; return ([implic_inst], unitBag (L span bind))
; return (irreds,binds)
}
where
- try_me inst = ReduceMe AddSCs
+ try_me _ = ReduceMe AddSCs
-- Here's the try-hard bit
-----------------------------------------------------------
t_a to 'a', where 'a' is the skolem from test5's signatures (due to the
Modular s a predicate in that signature). If we don't zonk (Modular s t_a) in
the givens, we will get into a loop as improveOne uses the unification engine
-TcGadt.tcUnifyTys, which doesn't know about mutable type variables.
+Unify.tcUnifyTys, which doesn't know about mutable type variables.
Note [LOOP]
; return binds1 }
where
env = mkRedEnv (pprInstLoc loc) try_me givens
- try_me inst = ReduceMe NoSCs
+ try_me _ = ReduceMe NoSCs
-- Like tryHardCheckLoop, but with NoSCs
\end{code}
-- BUT do no improvement! See Plan D above
-- HOWEVER, some unification may take place, if we instantiate
-- a method Inst with an equality constraint
- ; let env = mkNoImproveRedEnv doc (\i -> ReduceMe AddSCs)
+ ; let env = mkNoImproveRedEnv doc (\_ -> ReduceMe AddSCs)
; (_imp, _binds, constrained_dicts, elim_skolems)
<- reduceContext env wanteds'
; elim_skolems
-- Warn in the mono
; warn_mono <- doptM Opt_WarnMonomorphism
; warnTc (warn_mono && (constrained_tvs' `intersectsVarSet` qtvs1))
- (vcat[ ptext SLIT("the Monomorphism Restriction applies to the binding")
- <> plural bndrs <+> ptext SLIT("for") <+> pp_bndrs,
- ptext SLIT("Consider giving a type signature for") <+> pp_bndrs])
+ (vcat[ ptext (sLit "the Monomorphism Restriction applies to the binding")
+ <> plural bndrs <+> ptext (sLit "for") <+> pp_bndrs,
+ ptext (sLit "Consider giving a type signature for") <+> pp_bndrs])
; traceTc (text "tcSimplifyRestricted" <+> vcat [
pprInsts wanteds, pprInsts constrained_dicts',
, red_givens :: [Inst] -- All guaranteed rigid
-- Always dicts
-- but see Note [Rigidity]
- , red_reft :: Refinement -- The refinement to apply to the 'givens'
- -- You should think of it as 'given equalities'
, red_stack :: (Int, [Inst]) -- Recursion stack (for err msg)
-- See Note [RedStack]
}
mkRedEnv doc try_me givens
= RedEnv { red_doc = doc, red_try_me = try_me,
red_givens = givens,
- red_reft = emptyRefinement,
red_stack = (0,[]),
red_improve = True }
-- Do not do improvement; no givens
mkNoImproveRedEnv doc try_me
= RedEnv { red_doc = doc, red_try_me = try_me,
- red_givens = [], red_reft = emptyRefinement,
+ red_givens = [],
red_stack = (0,[]),
red_improve = True }
; let givens = red_givens env
(given_eqs0, given_dicts0) = partition isEqInst givens
(wanted_eqs0, wanted_non_eqs) = partition isEqInst wanteds
- (wanted_implics0, wanted_dicts0) = partition isImplicInst wanted_non_eqs
+ (wanted_implics0, wanted_dicts) = partition isImplicInst wanted_non_eqs
-- We want to add as wanted equalities those that (transitively)
-- occur in superclass contexts of wanted class constraints.
-- See Note [Ancestor Equalities]
- ; ancestor_eqs <- ancestorEqualities wanted_dicts0
+ ; ancestor_eqs <- ancestorEqualities wanted_dicts
; let wanted_eqs = wanted_eqs0 ++ ancestor_eqs
; traceTc $ text "reduceContext: ancestor eqs" <+> ppr ancestor_eqs
given_dicts0
-- 5. Build the Avail mapping from "given_dicts"
- -- Add dicts refined by the current type refinement
- ; (init_state, extra_givens) <- getLIE $ do
+ ; (init_state, _) <- getLIE $ do
{ init_state <- foldlM addGiven emptyAvails given_dicts
- ; let reft = red_reft env
- ; if isEmptyRefinement reft then return init_state
- else foldlM (addRefinedGiven reft)
- init_state given_dicts }
+ ; return init_state
+ }
- -- *** ToDo: what to do with the "extra_givens"? For the
+ -- !!! ToDo: what to do with the "extra_givens"? For the
-- moment I'm simply discarding them, which is probably wrong
- -- 7. Normalise the *wanted* *dictionary* constraints
- -- wrt. the toplevel and given equations
- -- NB: normalisation includes zonking as part of what it does
- -- so it's important to do it after any unifications
- -- that happened as a result of the addGivens
- ; (wanted_dicts,normalise_binds1) <- normaliseWantedDicts given_eqs wanted_dicts0
-
-- 6. Solve the *wanted* *dictionary* constraints (not implications)
-- This may expose some further equational constraints...
; (avails, extra_eqs) <- getLIE (reduceList env wanted_dicts init_state)
- ; (dict_binds, bound_dicts, dict_irreds) <- extractResults avails wanted_dicts
+ ; (dict_binds, bound_dicts, dict_irreds)
+ <- extractResults avails wanted_dicts
; traceTc $ text "reduceContext extractresults" <+> vcat
- [ppr avails,ppr wanted_dicts,ppr dict_binds]
-
- -- *** ToDo: what to do with the "extra_eqs"? For the
- -- moment I'm simply discarding them, which is probably wrong
+ [ppr avails, ppr wanted_dicts, ppr dict_binds]
-- Solve the wanted *implications*. In doing so, we can provide
-- as "given" all the dicts that were originally given,
-- *or* for which we now have bindings,
-- *or* which are now irreds
- ; let implic_env = env { red_givens = givens ++ bound_dicts ++ dict_irreds }
- ; (implic_binds_s, implic_irreds_s) <- mapAndUnzipM (reduceImplication implic_env) wanted_implics0
+ ; let implic_env = env { red_givens = givens ++ bound_dicts
+ ++ dict_irreds }
+ ; (implic_binds_s, implic_irreds_s)
+ <- mapAndUnzipM (reduceImplication implic_env) wanted_implics0
; let implic_binds = unionManyBags implic_binds_s
implic_irreds = concat implic_irreds_s
- -- 3. Solve the *wanted* *equation* constraints
- ; eq_irreds0 <- solveWantedEqs given_eqs wanted_eqs
+ -- Normalise the wanted equality constraints
+ ; eq_irreds <- normaliseWantedEqs given_eqs (wanted_eqs ++ extra_eqs)
- -- 4. Normalise the *wanted* equality constraints with respect to
- -- each other
- ; eq_irreds <- normaliseWantedEqs eq_irreds0
-
- -- 8. Substitute the wanted *equations* in the wanted *dictionaries*
+ -- Normalise the wanted dictionaries
; let irreds = dict_irreds ++ implic_irreds
- ; (norm_irreds, normalise_binds2) <- substEqInDictInsts True {-wanted-}
- eq_irreds irreds
+ eqs = eq_irreds ++ given_eqs
+ ; (norm_irreds, normalise_binds) <- normaliseWantedDicts eqs irreds
- -- 9. eliminate the artificial skolem constants introduced in 1.
--- ; eliminate_skolems
-
- -- Figure out whether we should go round again
- -- My current plan is to see if any of the mutable tyvars in
- -- givens or irreds has been filled in by improvement.
- -- If so, there is merit in going around again, because
- -- we may make further progress
+ -- Figure out whether we should go round again. We do so in either
+ -- two cases:
+ -- (1) If any of the mutable tyvars in givens or irreds has been
+ -- filled in by improvement, there is merit in going around
+ -- again, because we may make further progress.
+ -- (2) If we managed to normalise any dicts, there is merit in going
+ -- around gain, because reduceList may be able to get further.
--
- -- ToDo: is it only mutable stuff? We may have exposed new
+ -- ToDo: We may have exposed new
-- equality constraints and should probably go round again
-- then as well. But currently we are dropping them on the
-- floor anyway.
; let all_irreds = norm_irreds ++ eq_irreds
- ; improved <- anyM isFilledMetaTyVar $ varSetElems $
- tyVarsOfInsts (givens ++ all_irreds)
+ ; improvedMetaTy <- anyM isFilledMetaTyVar $ varSetElems $
+ tyVarsOfInsts (givens ++ all_irreds)
+ ; let improvedDicts = not $ isEmptyBag normalise_binds
+ improved = improvedMetaTy || improvedDicts
-- The old plan (fragile)
-- improveed = availsImproved avails
]))
; return (improved,
- given_binds `unionBags` normalise_binds1
- `unionBags` normalise_binds2
+ given_binds `unionBags` normalise_binds
`unionBags` dict_binds
`unionBags` implic_binds,
all_irreds,
-> TcM ImprovementDone
unifyEqns [] = return False
unifyEqns eqns
- = do { traceTc (ptext SLIT("Improve:") <+> vcat (map pprEquationDoc eqns))
+ = do { traceTc (ptext (sLit "Improve:") <+> vcat (map pprEquationDoc eqns))
; mapM_ unify eqns
; return True }
where
mapM_ (unif_pr tenv) pairs
unif_pr tenv (ty1,ty2) = unifyType (substTy tenv ty1) (substTy tenv ty2)
-pprEquationDoc (eqn, (p1,w1), (p2,w2)) = vcat [pprEquation eqn, nest 2 (ppr p1), nest 2 (ppr p2)]
+pprEquationDoc :: (Equation, (PredType, SDoc), (PredType, SDoc)) -> SDoc
+pprEquationDoc (eqn, (p1, _), (p2, _)) = vcat [pprEquation eqn, nest 2 (ppr p1), nest 2 (ppr p2)]
+mkEqnMsg :: (TcPredType, SDoc) -> (TcPredType, SDoc) -> TidyEnv
+ -> TcM (TidyEnv, SDoc)
mkEqnMsg (pred1,from1) (pred2,from2) tidy_env
= do { pred1' <- zonkTcPredType pred1; pred2' <- zonkTcPredType pred2
; let { pred1'' = tidyPred tidy_env pred1'; pred2'' = tidyPred tidy_env pred2' }
- ; let msg = vcat [ptext SLIT("When using functional dependencies to combine"),
+ ; let msg = vcat [ptext (sLit "When using functional dependencies to combine"),
nest 2 (sep [ppr pred1'' <> comma, nest 2 from1]),
nest 2 (sep [ppr pred2'' <> comma, nest 2 from2])]
; return (tidy_env, msg) }
reduceList env@(RedEnv {red_stack = (n,stk)}) wanteds state
= do { traceTc (text "reduceList " <+> (ppr wanteds $$ ppr state))
; dopts <- getDOpts
-#ifdef DEBUG
- ; if n > 8 then
- dumpTcRn (hang (ptext SLIT("Interesting! Context reduction stack depth") <+> int n)
+ ; when (debugIsOn && (n > 8)) $ do
+ debugDumpTcRn (hang (ptext (sLit "Interesting! Context reduction stack depth") <+> int n)
2 (ifPprDebug (nest 2 (pprStack stk))))
- else return ()
-#endif
; if n >= ctxtStkDepth dopts then
failWithTc (reduceDepthErr n stk)
else
; go ws state' }
-- Base case: we're done!
+reduce :: RedEnv -> Inst -> Avails -> TcM Avails
reduce env wanted avails
-- It's the same as an existing inst, or a superclass thereof
- | Just avail <- findAvail avails wanted
+ | Just _ <- findAvail avails wanted
= do { traceTc (text "reduce: found " <+> ppr wanted)
; return avails
}
= do { res <- lookupSimpleInst wanted
; case res of
GenInst [] rhs -> addWanted AddSCs avails wanted rhs []
- other -> do_this_otherwise avails wanted }
+ _ -> do_this_otherwise avails wanted }
\end{code}
\begin{code}
---------------------------------------------
reduceInst :: RedEnv -> Avails -> Inst -> TcM (Avails, LookupInstResult)
-reduceInst env avails other_inst
+reduceInst _ avails other_inst
= do { result <- lookupSimpleInst other_inst
; return (avails, result) }
\end{code}
Suppose we are simplifying the constraint
forall bs. extras => wanted
-in the context of an overall simplification problem with givens 'givens',
-and refinment 'reft'.
+in the context of an overall simplification problem with givens 'givens'.
Note that
- * The refinement is often empty
-
- * The 'extra givens' need not mention any of the quantified type variables
+ * The 'givens' need not mention any of the quantified type variables
e.g. forall {}. Eq a => Eq [a]
forall {}. C Int => D (Tree Int)
--
reduceImplication env
orig_implic@(ImplicInst { tci_name = name, tci_loc = inst_loc,
- tci_tyvars = tvs, tci_reft = reft,
+ tci_tyvars = tvs,
tci_given = extra_givens, tci_wanted = wanteds })
- = do { -- Add refined givens, and the extra givens
- -- Todo fix this
--- (refined_red_givens,refined_avails)
--- <- if isEmptyRefinement reft then return (red_givens env,orig_avails)
--- else foldlM (addRefinedGiven reft) ([],orig_avails) (red_givens env)
--- Commented out SLPJ Sept 07; see comment with extractLocalResults below
- let refined_red_givens = []
-
- -- Solve the sub-problem
- ; let try_me inst = ReduceMe AddSCs -- Note [Freeness and implications]
+ = do { -- Solve the sub-problem
+ ; let try_me _ = ReduceMe AddSCs -- Note [Freeness and implications]
env' = env { red_givens = extra_givens ++ red_givens env
- , red_reft = reft
- , red_doc = sep [ptext SLIT("reduceImplication for") <+> ppr name,
- nest 2 (parens $ ptext SLIT("within") <+> red_doc env)]
+ , red_doc = sep [ptext (sLit "reduceImplication for")
+ <+> ppr name,
+ nest 2 (parens $ ptext (sLit "within")
+ <+> red_doc env)]
, red_try_me = try_me }
; traceTc (text "reduceImplication" <+> vcat
[ ppr (red_givens env), ppr extra_givens,
- ppr reft, ppr wanteds])
+ ppr wanteds])
; (irreds, binds) <- checkLoop env' wanteds
; let (extra_eq_givens, extra_dict_givens) = partition isEqInst extra_givens
-- SLPJ Sept 07: I think this is bogus; currently
-- If there are any irreds, we back off and do nothing
return (emptyBag, [orig_implic])
else do
- { (simpler_implic_insts, bind) <- makeImplicationBind inst_loc tvs reft extra_givens irreds
- -- This binding is useless if the recursive simplification
- -- made no progress; but currently we don't try to optimise that
- -- case. After all, we only try hard to reduce at top level, or
- -- when inferring types.
+ { (simpler_implic_insts, bind)
+ <- makeImplicationBind inst_loc tvs extra_givens irreds
+ -- This binding is useless if the recursive simplification
+ -- made no progress; but currently we don't try to optimise that
+ -- case. After all, we only try hard to reduce at top level, or
+ -- when inferring types.
; let dict_wanteds = filter (not . isEqInst) wanteds
-- TOMDO: given equational constraints bug!
<.> WpLet (binds `unionBags` bind)
wrap_inline | null dict_ids = idHsWrapper
| otherwise = WpInline
- rhs = mkHsWrap co payload
+ rhs = mkLHsWrap co payload
loc = instLocSpan inst_loc
- payload | [dict_wanted] <- dict_wanteds = HsVar (instToId dict_wanted)
- | otherwise = ExplicitTuple (map (L loc . HsVar . instToId) dict_wanteds) Boxed
+ payload = mkBigLHsTup (map (L loc . HsVar . instToId) dict_wanteds)
; traceTc (vcat [text "reduceImplication" <+> ppr name,
ppr simpler_implic_insts,
text "->" <+> ppr rhs])
- ; return (unitBag (L loc (VarBind (instToId orig_implic) (L loc rhs))),
+ ; return (unitBag (L loc (VarBind (instToId orig_implic) rhs)),
simpler_implic_insts)
}
}
+reduceImplication _ i = pprPanic "reduceImplication" (ppr i)
\end{code}
Note [Always inline implication constraints]
to float the (C Int) out, even though it mentions no type variable in
the constraints!
+One more example: the constraint
+ class C a => D a b
+ instance (C a, E c) => E (a,c)
+
+ constraint: forall b. D Int b => E (Int,c)
+
+You might think that the (D Int b) can't possibly contribute
+to solving (E (Int,c)), since the latter mentions 'c'. But
+in fact it can, because solving the (E (Int,c)) constraint needs
+dictionaries
+ C Int, E c
+and the (C Int) can be satisfied from the superclass of (D Int b).
+So we must still not float (E (Int,c)) out.
+
+To think about: special cases for unary type classes?
+
Note [Pruning the givens in an implication constraint]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Suppose we are about to form the implication constraint
forall tvs. Eq a => Ord b
The (Eq a) cannot contribute to the (Ord b), because it has no access to
the type variable 'b'. So we could filter out the (Eq a) from the givens.
+But BE CAREFUL of the examples above in [Freeness and implications].
Doing so would be a bit tidier, but all the implication constraints get
simplified away by the optimiser, so it's no great win. So I don't take
instance Outputable Avails where
ppr = pprAvails
+pprAvails :: Avails -> SDoc
pprAvails (Avails imp avails)
- = vcat [ ptext SLIT("Avails") <> (if imp then ptext SLIT("[improved]") else empty)
+ = vcat [ ptext (sLit "Avails") <> (if imp then ptext (sLit "[improved]") else empty)
, nest 2 $ braces $
vcat [ sep [ppr inst, nest 2 (equals <+> ppr avail)]
| (inst,avail) <- fmToList avails ]]
availsInsts :: Avails -> [Inst]
availsInsts (Avails _ avails) = keysFM avails
-availsImproved (Avails imp _) = imp
-
-updateImprovement :: Avails -> Avails -> Avails
--- (updateImprovement a1 a2) sets a1's improvement flag from a2
-updateImprovement (Avails _ avails1) (Avails imp2 _) = Avails imp2 avails1
+_availsImproved :: Avails -> ImprovementDone
+_availsImproved (Avails imp _) = imp
\end{code}
Extracting the bindings from a bunch of Avails.
-> DoneEnv -- Has an entry for each inst in the above three sets
-> [Inst] -- Wanted
-> TcM (TcDictBinds, [Inst], [Inst])
- go binds bound_dicts irreds done []
+ go binds bound_dicts irreds _ []
= return (binds, bound_dicts, irreds)
go binds bound_dicts irreds done (w:ws)
-- No ASSERT( not (given `elemAvails` avails) ) because in an instance
-- decl for Ord t we can add both Ord t and Eq t as 'givens',
-- so the assert isn't true
-
-addRefinedGiven :: Refinement -> Avails -> Inst -> TcM Avails
-addRefinedGiven reft avails given
- | isDict given -- We sometimes have 'given' methods, but they
- -- are always optional, so we can drop them
- , let pred = dictPred given
- , isRefineablePred pred -- See Note [ImplicInst rigidity]
- , Just (co, pred) <- refinePred reft pred
- = do { new_given <- newDictBndr (instLoc given) pred
- ; let rhs = L (instSpan given) $
- HsWrap (WpCo co) (HsVar (instToId given))
- ; addAvailAndSCs AddSCs avails new_given (Rhs rhs [given]) }
- -- ToDo: the superclasses of the original given all exist in Avails
- -- so we could really just cast them, but it's more awkward to do,
- -- and hopefully the optimiser will spot the duplicated work
- | otherwise
- = return avails
\end{code}
-Note [ImplicInst rigidity]
-~~~~~~~~~~~~~~~~~~~~~~~~~~
-Consider
- C :: forall ab. (Eq a, Ord b) => b -> T a
-
- ...(case x of C v -> <body>)...
-
-From the case (where x::T ty) we'll get an implication constraint
- forall b. (Eq ty, Ord b) => <body-constraints>
-Now suppose <body-constraints> itself has an implication constraint
-of form
- forall c. <reft> => <payload>
-Then, we can certainly apply the refinement <reft> to the Ord b, becuase it is
-existential, but we probably should not apply it to the (Eq ty) because it may
-be wobbly. Hence the isRigidInst
-
-@Insts@ are ordered by their class/type info, rather than by their
-unique. This allows the context-reduction mechanism to use standard finite
-maps to do their stuff. It's horrible that this code is here, rather
-than with the Avails handling stuff in TcSimplify
-
\begin{code}
addIrred :: WantSCs -> Avails -> Inst -> TcM Avails
addIrred want_scs avails irred = ASSERT2( not (irred `elemAvails` avails), ppr irred $$ ppr avails )
-- Watch out, though. Since the avails may contain loops
-- (see Note [RECURSIVE DICTIONARIES]), so we need to track the ones we've seen so far
findAllDeps so_far (Rhs _ kids) = foldl find_all so_far kids
- findAllDeps so_far other = so_far
+ findAllDeps so_far _ = so_far
find_all :: IdSet -> Inst -> IdSet
find_all so_far kid
is_given :: Inst -> Bool
is_given sc_dict = case findAvail avails sc_dict of
Just (Given _) -> True -- Given is cheaper than superclass selection
- other -> False
+ _ -> False
-- From the a set of insts obtain all equalities that (transitively) occur in
-- superclass contexts of class constraints (aka the ancestor equalities).
-- The TcLclEnv should be valid here, solely to improve
-- error message generation for the monomorphism restriction
+tc_simplify_top :: SDoc -> Bool -> [Inst] -> TcM (Bag (LHsBind TcId))
tc_simplify_top doc interactive wanteds
= do { dflags <- getDOpts
; wanteds <- zonkInsts wanteds
; (irreds1, binds1) <- tryHardCheckLoop doc1 wanteds
-- ; (irreds1, binds1) <- gentleInferLoop doc1 wanteds
; traceTc (text "tc_simplify_top 1: " <+> ppr irreds1)
- ; (irreds2, binds2) <- approximateImplications doc2 (\d -> True) irreds1
+ ; (irreds2, binds2) <- approximateImplications doc2 (\_ -> True) irreds1
; traceTc (text "tc_simplify_top 2: " <+> ppr irreds2)
-- Use the defaulting rules to do extra unification
; return (binds1 `unionBags` binds2 `unionBags` binds3) }
where
- doc1 = doc <+> ptext SLIT("(first round)")
- doc2 = doc <+> ptext SLIT("(approximate)")
- doc3 = doc <+> ptext SLIT("(disambiguate)")
+ doc1 = doc <+> ptext (sLit "(first round)")
+ doc2 = doc <+> ptext (sLit "(approximate)")
+ doc3 = doc <+> ptext (sLit "(disambiguate)")
\end{code}
If a dictionary constrains a type variable which is
| extended_defaulting = any isInteractiveClass clss
| otherwise = all is_std_class clss && (any is_num_class clss)
- -- In interactive mode, or with -fextended-default-rules,
+ -- In interactive mode, or with -XExtendedDefaultRules,
-- we default Show a to Show () to avoid graututious errors on "show []"
isInteractiveClass cls
= is_num_class cls || (classKey cls `elem` [showClassKey, eqClassKey, ordClassKey])
opt_deflt ovl_strings string_ty) } } }
where
opt_deflt True ty = [ty]
- opt_deflt False ty = []
+ opt_deflt False _ = []
\end{code}
Note [Default unitTy]
~~~~~~~~~~~~~~~~~~~~~
-In interative mode (or with -fextended-default-rules) we add () as the first type we
+In interative mode (or with -XExtendedDefaultRules) we add () as the first type we
try when defaulting. This has very little real impact, except in the following case.
Consider:
Text.Printf.printf "hello"
; return simpl_theta }
where
- doc = ptext SLIT("deriving classes for a data type")
+ doc = ptext (sLit "deriving classes for a data type")
ok dict | isDict dict = validDerivPred (dictPred dict)
| otherwise = False
if null irreds then
return ()
else
- traceTc (ptext SLIT("tcSimplifyDefault failing")) >> failM
+ traceTc (ptext (sLit "tcSimplifyDefault failing")) >> failM
where
- doc = ptext SLIT("default declaration")
+ doc = ptext (sLit "default declaration")
\end{code}
-- Group together insts with the same origin
-- We want to report them together in error messages
-groupErrs report_err []
+groupErrs _ []
= return ()
groupErrs report_err (inst:insts)
= do { do_one (inst:friends)
addInstLoc insts msg = msg $$ nest 2 (pprInstArising (head insts))
addTopIPErrs :: [Name] -> [Inst] -> TcM ()
-addTopIPErrs bndrs []
+addTopIPErrs _ []
= return ()
addTopIPErrs bndrs ips
= do { dflags <- getDOpts
where
(tidy_env, tidy_ips) = tidyInsts ips
mk_msg dflags ips
- = vcat [sep [ptext SLIT("Implicit parameters escape from"),
- nest 2 (ptext SLIT("the monomorphic top-level binding")
- <> plural bndrs <+> ptext SLIT("of")
+ = vcat [sep [ptext (sLit "Implicit parameters escape from"),
+ nest 2 (ptext (sLit "the monomorphic top-level binding")
+ <> plural bndrs <+> ptext (sLit "of")
<+> pprBinders bndrs <> colon)],
nest 2 (vcat (map ppr_ip ips)),
monomorphism_fix dflags]
where
(tidy_env, tidy_dicts) = tidyInsts dicts
report dicts = addErrTcM (tidy_env, mk_msg dicts)
- mk_msg dicts = addInstLoc dicts (ptext SLIT("Unbound implicit parameter") <>
+ mk_msg dicts = addInstLoc dicts (ptext (sLit "Unbound implicit parameter") <>
plural tidy_dicts <+> pprDictsTheta tidy_dicts)
addNoInstanceErrs :: [Inst] -- Wanted (can include implications)
reportNoInstances tidy_env mb_what insts
= groupErrs (report_no_instances tidy_env mb_what) insts
+report_no_instances :: TidyEnv -> Maybe (InstLoc, [Inst]) -> [Inst] -> TcM ()
report_no_instances tidy_env mb_what insts
= do { inst_envs <- tcGetInstEnvs
; let (implics, insts1) = partition isImplicInst insts
| not (isClassDict wanted) = Left wanted
| otherwise
= case lookupInstEnv inst_envs clas tys of
+ ([], _) -> Left wanted -- No match
-- The case of exactly one match and no unifiers means a
-- successful lookup. That can't happen here, because dicts
-- only end up here if they didn't match in Inst.lookupInst
-#ifdef DEBUG
- ([m],[]) -> pprPanic "reportNoInstance" (ppr wanted)
-#endif
- ([], _) -> Left wanted -- No match
- res -> Right (mk_overlap_msg wanted res)
+ ([_],[])
+ | debugIsOn -> pprPanic "reportNoInstance" (ppr wanted)
+ res -> Right (mk_overlap_msg wanted res)
where
(clas,tys) = getDictClassTys wanted
mk_overlap_msg dict (matches, unifiers)
= ASSERT( not (null matches) )
- vcat [ addInstLoc [dict] ((ptext SLIT("Overlapping instances for")
+ vcat [ addInstLoc [dict] ((ptext (sLit "Overlapping instances for")
<+> pprPred (dictPred dict))),
- sep [ptext SLIT("Matching instances") <> colon,
+ sep [ptext (sLit "Matching instances") <> colon,
nest 2 (vcat [pprInstances ispecs, pprInstances unifiers])],
if not (isSingleton matches)
then -- Two or more matches
empty
else -- One match, plus some unifiers
ASSERT( not (null unifiers) )
- parens (vcat [ptext SLIT("The choice depends on the instantiation of") <+>
+ parens (vcat [ptext (sLit "The choice depends on the instantiation of") <+>
quotes (pprWithCommas ppr (varSetElems (tyVarsOfInst dict))),
- ptext SLIT("To pick the first instance above, use -fallow-incoherent-instances"),
- ptext SLIT("when compiling the other instance declarations")])]
+ ptext (sLit "To pick the first instance above, use -XIncoherentInstances"),
+ ptext (sLit "when compiling the other instance declarations")])]
where
ispecs = [ispec | (ispec, _) <- matches]
| Just (loc, givens) <- mb_what, -- Nested (type signatures, instance decls)
not (isEmptyVarSet (tyVarsOfInsts insts))
= vcat [ addInstLoc insts $
- sep [ ptext SLIT("Could not deduce") <+> pprDictsTheta insts
- , nest 2 $ ptext SLIT("from the context") <+> pprDictsTheta givens]
+ sep [ ptext (sLit "Could not deduce") <+> pprDictsTheta insts
+ , nest 2 $ ptext (sLit "from the context") <+> pprDictsTheta givens]
, show_fixes (fix1 loc : fixes2) ]
| otherwise -- Top level
= vcat [ addInstLoc insts $
- ptext SLIT("No instance") <> plural insts
- <+> ptext SLIT("for") <+> pprDictsTheta insts
+ ptext (sLit "No instance") <> plural insts
+ <+> ptext (sLit "for") <+> pprDictsTheta insts
, show_fixes fixes2 ]
where
- fix1 loc = sep [ ptext SLIT("add") <+> pprDictsTheta insts
- <+> ptext SLIT("to the context of"),
+ fix1 loc = sep [ ptext (sLit "add") <+> pprDictsTheta insts
+ <+> ptext (sLit "to the context of"),
nest 2 (ppr (instLocOrigin loc)) ]
-- I'm not sure it helps to add the location
- -- nest 2 (ptext SLIT("at") <+> ppr (instLocSpan loc)) ]
+ -- nest 2 (ptext (sLit "at") <+> ppr (instLocSpan loc)) ]
fixes2 | null instance_dicts = []
- | otherwise = [sep [ptext SLIT("add an instance declaration for"),
+ | otherwise = [sep [ptext (sLit "add an instance declaration for"),
pprDictsTheta instance_dicts]]
instance_dicts = [d | d <- insts, isClassDict d, not (isTyVarDict d)]
-- Insts for which it is worth suggesting an adding an instance declaration
show_fixes :: [SDoc] -> SDoc
show_fixes [] = empty
- show_fixes (f:fs) = sep [ptext SLIT("Possible fix:"),
- nest 2 (vcat (f : map (ptext SLIT("or") <+>) fs))]
+ show_fixes (f:fs) = sep [ptext (sLit "Possible fix:"),
+ nest 2 (vcat (f : map (ptext (sLit "or") <+>) fs))]
+addTopAmbigErrs :: [Inst] -> TcRn ()
addTopAmbigErrs dicts
-- Divide into groups that share a common set of ambiguous tyvars
= ifErrsM (return ()) $ -- Only report ambiguity if no other errors happened
; return (tidy_env, mk_msg dflags docs) }
where
mk_msg _ _ | any isRuntimeUnk inst_tvs
- = vcat [ptext SLIT("Cannot resolve unknown runtime types:") <+>
+ = vcat [ptext (sLit "Cannot resolve unknown runtime types:") <+>
(pprWithCommas ppr inst_tvs),
- ptext SLIT("Use :print or :force to determine these types")]
- mk_msg _ [] = ptext SLIT("Probable fix: add a type signature that fixes these type variable(s)")
+ ptext (sLit "Use :print or :force to determine these types")]
+ mk_msg _ [] = ptext (sLit "Probable fix: add a type signature that fixes these type variable(s)")
-- This happens in things like
-- f x = show (read "foo")
-- where monomorphism doesn't play any role
mk_msg dflags docs
- = vcat [ptext SLIT("Possible cause: the monomorphism restriction applied to the following:"),
+ = vcat [ptext (sLit "Possible cause: the monomorphism restriction applied to the following:"),
nest 2 (vcat docs),
monomorphism_fix dflags]
monomorphism_fix :: DynFlags -> SDoc
monomorphism_fix dflags
- = ptext SLIT("Probable fix:") <+> vcat
- [ptext SLIT("give these definition(s) an explicit type signature"),
+ = ptext (sLit "Probable fix:") <+> vcat
+ [ptext (sLit "give these definition(s) an explicit type signature"),
if dopt Opt_MonomorphismRestriction dflags
- then ptext SLIT("or use -fno-monomorphism-restriction")
- else empty] -- Only suggest adding "-fno-monomorphism-restriction"
+ then ptext (sLit "or use -XNoMonomorphismRestriction")
+ else empty] -- Only suggest adding "-XNoMonomorphismRestriction"
-- if it is not already set!
+warnDefault :: [(Inst, Class, Var)] -> Type -> TcM ()
warnDefault ups default_ty = do
warn_flag <- doptM Opt_WarnTypeDefaults
addInstCtxt (instLoc (head (dicts))) (warnTc warn_flag warn_msg)
-- Tidy them first
(_, tidy_dicts) = tidyInsts dicts
- warn_msg = vcat [ptext SLIT("Defaulting the following constraint(s) to type") <+>
+ warn_msg = vcat [ptext (sLit "Defaulting the following constraint(s) to type") <+>
quotes (ppr default_ty),
pprDictsInFull tidy_dicts]
+reduceDepthErr :: Int -> [Inst] -> SDoc
reduceDepthErr n stack
- = vcat [ptext SLIT("Context reduction stack overflow; size =") <+> int n,
- ptext SLIT("Use -fcontext-stack=N to increase stack size to N"),
+ = vcat [ptext (sLit "Context reduction stack overflow; size =") <+> int n,
+ ptext (sLit "Use -fcontext-stack=N to increase stack size to N"),
nest 4 (pprStack stack)]
+pprStack :: [Inst] -> SDoc
pprStack stack = vcat (map pprInstInFull stack)
\end{code}
projects / ghc-hetmet.git / blobdiff