import Var ( TyVar )
import Name ( getOccName, getSrcLoc )
import NameSet ( NameSet, mkNameSet, elemNameSet )
-import Class ( classBigSig )
+import Class ( classBigSig, classKey )
import FunDeps ( oclose, grow, improve, pprEquationDoc )
import PrelInfo ( isNumericClass, isCreturnableClass, isCcallishClass )
-import PrelNames ( splitName, fstName, sndName )
+import PrelNames ( splitName, fstName, sndName, showClassKey, eqClassKey, ordClassKey)
+import HscTypes ( GhciMode(Interactive) )
import Subst ( mkTopTyVarSubst, substTheta, substTy )
import TysWiredIn ( unitTy, pairTyCon )
import FiniteMap
import Outputable
import ListSetOps ( equivClasses )
+import Unique ( hasKey )
import Util ( zipEqual, isSingleton )
import List ( partition )
import CmdLineOpts
| isClassDict inst = DontReduceUnlessConstant -- Dicts
| otherwise = ReduceMe -- Lits and Methods
in
+ traceTc (text "infloop" <+> vcat [ppr tau_tvs', ppr wanteds', ppr preds, ppr (grow preds tau_tvs'), ppr qtvs]) `thenM_`
-- Step 2
reduceContext doc try_me [] wanteds' `thenM` \ (no_improvement, frees, binds, irreds) ->
= -- Step 1
mappM zonkInst givens `thenM` \ givens' ->
mappM zonkInst wanteds `thenM` \ wanteds' ->
- get_qtvs `thenM` \ qtvs' ->
+ get_qtvs `thenM` \ qtvs' ->
-- Step 2
let
-- foo = f (3::Int)
-- We want to infer the polymorphic type
-- foo :: forall b. b -> b
- let
- try_me inst = ReduceMe -- Reduce as far as we can. Don't stop at
- -- dicts; the idea is to get rid of as many type
- -- variables as possible, and we don't want to stop
- -- at (say) Monad (ST s), because that reduces
- -- immediately, with no constraint on s.
- in
- simpleReduceLoop doc try_me wanteds `thenM` \ (_, _, constrained_dicts) ->
+
+ -- 'reduceMe': Reduce as far as we can. Don't stop at
+ -- dicts; the idea is to get rid of as many type
+ -- variables as possible, and we don't want to stop
+ -- at (say) Monad (ST s), because that reduces
+ -- immediately, with no constraint on s.
+ simpleReduceLoop doc reduceMe wanteds `thenM` \ (foo_frees, foo_binds, constrained_dicts) ->
-- Next, figure out the tyvars we will quantify over
zonkTcTyVarsAndFV (varSetElems tau_tvs) `thenM` \ tau_tvs' ->
qtvs = (tau_tvs' `minusVarSet` oclose (fdPredsOfInsts constrained_dicts) gbl_tvs)
`minusVarSet` constrained_tvs
in
+ traceTc (text "tcSimplifyRestricted" <+> vcat [
+ pprInsts wanteds, pprInsts foo_frees, pprInsts constrained_dicts,
+ ppr foo_binds,
+ ppr constrained_tvs, ppr tau_tvs', ppr qtvs ]) `thenM_`
-- The first step may have squashed more methods than
-- necessary, so try again, this time knowing the exact
-- Remember that we may need to do *some* simplification, to
-- (for example) squash {Monad (ST s)} into {}. It's not enough
-- just to float all constraints
- mappM zonkInst wanteds `thenM` \ wanteds' ->
+ restrict_loop doc qtvs wanteds
+ -- We still need a loop because improvement can take place
+ -- E.g. if we have (C (T a)) and the instance decl
+ -- instance D Int b => C (T a) where ...
+ -- and there's a functional dependency for D. Then we may improve
+ -- the tyep variable 'b'.
+
+restrict_loop doc qtvs wanteds
+ = mappM zonkInst wanteds `thenM` \ wanteds' ->
+ zonkTcTyVarsAndFV (varSetElems qtvs) `thenM` \ qtvs' ->
let
- try_me inst | isFreeWrtTyVars qtvs inst = Free
- | otherwise = ReduceMe
+ try_me inst | isFreeWrtTyVars qtvs' inst = Free
+ | otherwise = ReduceMe
in
reduceContext doc try_me [] wanteds' `thenM` \ (no_improvement, frees, binds, irreds) ->
- ASSERT( no_improvement )
- ASSERT( null irreds )
- -- No need to loop because simpleReduceLoop will have
- -- already done any improvement necessary
-
- extendLIEs frees `thenM_`
- returnM (varSetElems qtvs, binds)
+ if no_improvement then
+ ASSERT( null irreds )
+ extendLIEs frees `thenM_`
+ returnM (varSetElems qtvs', binds)
+ else
+ restrict_loop doc qtvs' (irreds ++ frees) `thenM` \ (qtvs1, binds1) ->
+ returnM (qtvs1, binds `AndMonoBinds` binds1)
\end{code}
\begin{code}
tcSimplifyBracket :: [Inst] -> TcM ()
tcSimplifyBracket wanteds
- = simpleReduceLoop doc try_me wanteds `thenM_`
+ = simpleReduceLoop doc reduceMe wanteds `thenM_`
returnM ()
-
where
- doc = text "tcSimplifyBracket"
- try_me inst = ReduceMe
+ doc = text "tcSimplifyBracket"
\end{code}
(tidy_env, tidy_dicts) = tidyInsts bad_guys
(bad_ips, non_ips) = partition isIPDict tidy_dicts
(no_insts, ambigs) = partition no_inst non_ips
- no_inst d = not (isTyVarDict d) || tyVarsOfInst d `subVarSet` fixed_tvs
- fixed_tvs = oclose (fdPredsOfInsts tidy_dicts) emptyVarSet
+ no_inst d = not (isTyVarDict d)
+ -- Previously, there was a more elaborate no_inst definition:
+ -- no_inst d = not (isTyVarDict d) || tyVarsOfInst d `subVarSet` fixed_tvs
+ -- fixed_tvs = oclose (fdPredsOfInsts tidy_dicts) emptyVarSet
+ -- But that seems over-elaborate to me; it only bites for class decls with
+ -- fundeps like this: class C a b | -> b where ...
in
-- Report definite errors
addTopAmbigErrs (tidy_env, ambigs) `thenM_`
-- Disambiguate the ones that look feasible
- mappM disambigGroup std_oks
+ getGhciMode `thenM` \ mode ->
+ mappM (disambigGroup mode) std_oks
) `thenM` \ binds_ambig ->
returnM (binds `andMonoBinds` andMonoBindList binds_ambig)
@void@.
\begin{code}
-disambigGroup :: [Inst] -- All standard classes of form (C a)
+disambigGroup :: GhciMode
+ -> [Inst] -- All standard classes of form (C a)
-> TcM TcDictBinds
-disambigGroup dicts
- | any isNumericClass classes -- Guaranteed all standard classes
- -- see comment at the end of function for reasons as to
+disambigGroup ghci_mode dicts
+ | any std_default_class classes -- Guaranteed all standard classes
+ -- See comment at the end of function for reasons as to
-- why the defaulting mechanism doesn't apply to groups that
-- include CCallable or CReturnable dicts.
&& not (any isCcallishClass classes)
in
-- See if any default works
tryM (try_default default_tys) `thenM` \ mb_ty ->
- case mb_ty of {
- Left _ -> -- If not, add an AmbigErr
- addTopAmbigErrs (tidyInsts dicts) `thenM_`
- returnM EmptyMonoBinds ;
+ case mb_ty of
+ Left _ -> bomb_out
+ Right chosen_default_ty -> choose_default chosen_default_ty
- Right chosen_default_ty ->
+ | all isCreturnableClass classes -- Default CCall stuff to ()
+ = choose_default unitTy
- -- If so, bind the type variable
+ | otherwise -- No defaults
+ = bomb_out
+
+ where
+ tyvar = get_tv (head dicts) -- Should be non-empty
+ classes = map get_clas dicts
+
+ std_default_class cls
+ = isNumericClass cls
+ || (ghci_mode == Interactive &&
+ classKey cls `elem` [showClassKey, eqClassKey, ordClassKey])
+ -- In interactive mode, we default Show a to Show ()
+ -- to avoid graututious errors on "show []"
+
+ choose_default default_ty -- Commit to tyvar = default_ty
+ = -- Bind the type variable
+ unifyTauTy default_ty (mkTyVarTy tyvar) `thenM_`
-- and reduce the context, for real this time
- unifyTauTy chosen_default_ty (mkTyVarTy tyvar) `thenM_`
- simpleReduceLoop (text "disambig" <+> ppr dicts)
+ simpleReduceLoop (text "disambig" <+> ppr dicts)
reduceMe dicts `thenM` \ (frees, binds, ambigs) ->
- WARN( not (null frees && null ambigs), ppr frees $$ ppr ambigs )
- warnDefault dicts chosen_default_ty `thenM_`
- returnM binds }
-
- | all isCreturnableClass classes
- = -- Default CCall stuff to (); we don't even both to check that () is an
- -- instance of CReturnable, because we know it is.
- unifyTauTy (mkTyVarTy tyvar) unitTy `thenM_`
- returnM EmptyMonoBinds
-
- | otherwise -- No defaults
- = addTopAmbigErrs (tidyInsts dicts) `thenM_`
- returnM EmptyMonoBinds
+ WARN( not (null frees && null ambigs), ppr frees $$ ppr ambigs )
+ warnDefault dicts default_ty `thenM_`
+ returnM binds
- where
- tyvar = get_tv (head dicts) -- Should be non-empty
- classes = map get_clas dicts
+ bomb_out = addTopAmbigErrs (tidyInsts dicts) `thenM_`
+ returnM EmptyMonoBinds
\end{code}
[Aside - why the defaulting mechanism is turned off when
projects / ghc-hetmet.git / blobdiff