%
% (c) The University of Glasgow 2006
% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
\section[TcBinds]{TcBinds}
\begin{code}
module TcBinds ( tcLocalBinds, tcTopBinds,
tcHsBootSigs, tcPolyBinds,
PragFun, tcSpecPrags, mkPragFun,
TcSigInfo(..), SigFun, mkSigFun,
badBootDeclErr ) where
import TcMatches ( tcGRHSsPat, tcMatchesFun )
import TcExpr ( tcMonoExpr )
import DynFlags
import HsSyn
import TcRnMonad
import TcEnv
import TcUnify
import TcSimplify
import TcHsType
import TcPat
import TcMType
import TcType
import RnBinds( misplacedSigErr )
import Coercion
import TysPrim
import Id
import Var
import Name
import NameSet
import NameEnv
import SrcLoc
import Bag
import ErrUtils
import Digraph
import Maybes
import Util
import BasicTypes
import Outputable
import FastString
import Data.List( partition )
import Control.Monad
#include "HsVersions.h"
\end{code}
%************************************************************************
%* *
\subsection{Type-checking bindings}
%* *
%************************************************************************
@tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because
it needs to know something about the {\em usage} of the things bound,
so that it can create specialisations of them. So @tcBindsAndThen@
takes a function which, given an extended environment, E, typechecks
the scope of the bindings returning a typechecked thing and (most
important) an LIE. It is this LIE which is then used as the basis for
specialising the things bound.
@tcBindsAndThen@ also takes a "combiner" which glues together the
bindings and the "thing" to make a new "thing".
The real work is done by @tcBindWithSigsAndThen@.
Recursive and non-recursive binds are handled in essentially the same
way: because of uniques there are no scoping issues left. The only
difference is that non-recursive bindings can bind primitive values.
Even for non-recursive binding groups we add typings for each binder
to the LVE for the following reason. When each individual binding is
checked the type of its LHS is unified with that of its RHS; and
type-checking the LHS of course requires that the binder is in scope.
At the top-level the LIE is sure to contain nothing but constant
dictionaries, which we resolve at the module level.
\begin{code}
tcTopBinds :: HsValBinds Name
-> TcM ( LHsBinds TcId
, [LTcSpecPrag]
, TcLclEnv)
tcTopBinds binds
= do { (ValBindsOut prs sigs, env) <- tcValBinds TopLevel binds getLclEnv
; let binds = foldr (unionBags . snd) emptyBag prs
; specs <- tcImpPrags sigs
; return (binds, specs, env) }
tcHsBootSigs :: HsValBinds Name -> TcM [Id]
tcHsBootSigs (ValBindsOut binds sigs)
= do { checkTc (null binds) badBootDeclErr
; mapM (addLocM tc_boot_sig) (filter isTypeLSig sigs) }
where
tc_boot_sig (TypeSig (L _ name) ty)
= do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
; return (mkVanillaGlobal name sigma_ty) }
tc_boot_sig s = pprPanic "tcHsBootSigs/tc_boot_sig" (ppr s)
tcHsBootSigs groups = pprPanic "tcHsBootSigs" (ppr groups)
badBootDeclErr :: Message
badBootDeclErr = ptext (sLit "Illegal declarations in an hs-boot file")
tcLocalBinds :: HsLocalBinds Name -> TcM thing
-> TcM (HsLocalBinds TcId, thing)
tcLocalBinds EmptyLocalBinds thing_inside
= do { thing <- thing_inside
; return (EmptyLocalBinds, thing) }
tcLocalBinds (HsValBinds binds) thing_inside
= do { (binds', thing) <- tcValBinds NotTopLevel binds thing_inside
; return (HsValBinds binds', thing) }
tcLocalBinds (HsIPBinds (IPBinds ip_binds _)) thing_inside
= do { (given_ips, ip_binds') <- mapAndUnzipM (wrapLocSndM tc_ip_bind) ip_binds
; (ev_binds, result) <- checkConstraints (IPSkol ips)
[] given_ips thing_inside
; return (HsIPBinds (IPBinds ip_binds' ev_binds), result) }
where
ips = [ip | L _ (IPBind ip _) <- ip_binds]
tc_ip_bind (IPBind ip expr)
= do { ty <- newFlexiTyVarTy argTypeKind
; ip_id <- newIP ip ty
; expr' <- tcMonoExpr expr ty
; return (ip_id, (IPBind (IPName ip_id) expr')) }
\end{code}
Note [Implicit parameter untouchables]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We add the type variables in the types of the implicit parameters
as untouchables, not so much because we really must not unify them,
but rather because we otherwise end up with constraints like this
Num alpha, Implic { wanted = alpha ~ Int }
The constraint solver solves alpha~Int by unification, but then
doesn't float that solved constraint out (it's not an unsolved
wanted. Result disaster: the (Num alpha) is again solved, this
time by defaulting. No no no.
However [Oct 10] this is all handled automatically by the
untouchable-range idea.
\begin{code}
tcValBinds :: TopLevelFlag
-> HsValBinds Name -> TcM thing
-> TcM (HsValBinds TcId, thing)
tcValBinds _ (ValBindsIn binds _) _
= pprPanic "tcValBinds" (ppr binds)
tcValBinds top_lvl (ValBindsOut binds sigs) thing_inside
= do {
; let { prag_fn = mkPragFun sigs (foldr (unionBags . snd) emptyBag binds)
; ty_sigs = filter isTypeLSig sigs
; sig_fn = mkSigFun ty_sigs }
; poly_ids <- checkNoErrs (mapAndRecoverM tcTySig ty_sigs)
; (binds', thing) <- tcExtendIdEnv poly_ids $
tcBindGroups top_lvl sig_fn prag_fn
binds thing_inside
; return (ValBindsOut binds' sigs, thing) }
tcBindGroups :: TopLevelFlag -> SigFun -> PragFun
-> [(RecFlag, LHsBinds Name)] -> TcM thing
-> TcM ([(RecFlag, LHsBinds TcId)], thing)
tcBindGroups _ _ _ [] thing_inside
= do { thing <- thing_inside
; return ([], thing) }
tcBindGroups top_lvl sig_fn prag_fn (group : groups) thing_inside
= do { (group', (groups', thing))
<- tc_group top_lvl sig_fn prag_fn group $
tcBindGroups top_lvl sig_fn prag_fn groups thing_inside
; return (group' ++ groups', thing) }
tc_group :: forall thing.
TopLevelFlag -> SigFun -> PragFun
-> (RecFlag, LHsBinds Name) -> TcM thing
-> TcM ([(RecFlag, LHsBinds TcId)], thing)
tc_group top_lvl sig_fn prag_fn (NonRecursive, binds) thing_inside
= do { (binds1, ids) <- tcPolyBinds top_lvl sig_fn prag_fn NonRecursive NonRecursive
(bagToList binds)
; thing <- tcExtendIdEnv ids thing_inside
; return ( [(NonRecursive, binds1)], thing) }
tc_group top_lvl sig_fn prag_fn (Recursive, binds) thing_inside
=
do { traceTc "tc_group rec" (pprLHsBinds binds)
; (binds1, _ids, thing) <- go sccs
; return ([(Recursive, binds1)], thing) }
where
sccs :: [SCC (LHsBind Name)]
sccs = stronglyConnCompFromEdgedVertices (mkEdges sig_fn binds)
go :: [SCC (LHsBind Name)] -> TcM (LHsBinds TcId, [TcId], thing)
go (scc:sccs) = do { (binds1, ids1) <- tc_scc scc
; (binds2, ids2, thing) <- tcExtendIdEnv ids1 $ go sccs
; return (binds1 `unionBags` binds2, ids1 ++ ids2, thing) }
go [] = do { thing <- thing_inside; return (emptyBag, [], thing) }
tc_scc (AcyclicSCC bind) = tc_sub_group NonRecursive [bind]
tc_scc (CyclicSCC binds) = tc_sub_group Recursive binds
tc_sub_group = tcPolyBinds top_lvl sig_fn prag_fn Recursive
mkEdges :: SigFun -> LHsBinds Name
-> [(LHsBind Name, BKey, [BKey])]
type BKey = Int
mkEdges sig_fn binds
= [ (bind, key, [key | n <- nameSetToList (bind_fvs (unLoc bind)),
Just key <- [lookupNameEnv key_map n], no_sig n ])
| (bind, key) <- keyd_binds
]
where
no_sig :: Name -> Bool
no_sig n = isNothing (sig_fn n)
keyd_binds = bagToList binds `zip` [0::BKey ..]
key_map :: NameEnv BKey
key_map = mkNameEnv [(bndr, key) | (L _ bind, key) <- keyd_binds
, bndr <- bindersOfHsBind bind ]
bindersOfHsBind :: HsBind Name -> [Name]
bindersOfHsBind (PatBind { pat_lhs = pat }) = collectPatBinders pat
bindersOfHsBind (FunBind { fun_id = L _ f }) = [f]
bindersOfHsBind (AbsBinds {}) = panic "bindersOfHsBind AbsBinds"
bindersOfHsBind (VarBind {}) = panic "bindersOfHsBind VarBind"
tcPolyBinds :: TopLevelFlag -> SigFun -> PragFun
-> RecFlag
-> RecFlag
-> [LHsBind Name]
-> TcM (LHsBinds TcId, [TcId])
tcPolyBinds top_lvl sig_fn prag_fn rec_group rec_tc bind_list
= setSrcSpan loc $
recoverM (recoveryCode binder_names sig_fn) $ do
{ traceTc "------------------------------------------------" empty
; traceTc "Bindings for" (ppr binder_names)
; tc_sig_fn <- tcInstSigs sig_fn binder_names
; dflags <- getDOpts
; let plan = decideGeneralisationPlan dflags top_lvl binder_names bind_list tc_sig_fn
; traceTc "Generalisation plan" (ppr plan)
; (binds, poly_ids) <- case plan of
NoGen -> tcPolyNoGen tc_sig_fn prag_fn rec_tc bind_list
InferGen mono -> tcPolyInfer top_lvl mono tc_sig_fn prag_fn rec_tc bind_list
CheckGen sig -> tcPolyCheck sig prag_fn rec_tc bind_list
; checkStrictBinds top_lvl rec_group bind_list poly_ids
; return (binds, poly_ids) }
where
binder_names = collectHsBindListBinders bind_list
loc = getLoc (head bind_list)
tcPolyNoGen
:: TcSigFun -> PragFun
-> RecFlag
-> [LHsBind Name]
-> TcM (LHsBinds TcId, [TcId])
tcPolyNoGen tc_sig_fn prag_fn rec_tc bind_list
= do { (binds', mono_infos) <- tcMonoBinds tc_sig_fn (LetGblBndr prag_fn)
rec_tc bind_list
; mono_ids' <- mapM tc_mono_info mono_infos
; return (binds', mono_ids') }
where
tc_mono_info (name, _, mono_id)
= do { mono_ty' <- zonkTcTypeCarefully (idType mono_id)
; let mono_id' = setIdType mono_id mono_ty'
; _specs <- tcSpecPrags mono_id' (prag_fn name)
; return mono_id' }
tcPolyCheck :: TcSigInfo -> PragFun
-> RecFlag
-> [LHsBind Name]
-> TcM (LHsBinds TcId, [TcId])
tcPolyCheck sig@(TcSigInfo { sig_id = id, sig_tvs = tvs, sig_scoped = scoped
, sig_theta = theta, sig_tau = tau, sig_loc = loc })
prag_fn rec_tc bind_list
= do { ev_vars <- newEvVars theta
; let skol_info = SigSkol (FunSigCtxt (idName id)) (mkPhiTy theta tau)
; (ev_binds, (binds', [mono_info]))
<- checkConstraints skol_info tvs ev_vars $
tcExtendTyVarEnv2 (scoped `zip` mkTyVarTys tvs) $
tcMonoBinds (\_ -> Just sig) LetLclBndr rec_tc bind_list
; export <- mkExport prag_fn tvs theta mono_info
; let (_, poly_id, _, _) = export
abs_bind = L loc $ AbsBinds
{ abs_tvs = tvs
, abs_ev_vars = ev_vars, abs_ev_binds = ev_binds
, abs_exports = [export], abs_binds = binds' }
; return (unitBag abs_bind, [poly_id]) }
tcPolyInfer
:: TopLevelFlag
-> Bool
-> TcSigFun -> PragFun
-> RecFlag
-> [LHsBind Name]
-> TcM (LHsBinds TcId, [TcId])
tcPolyInfer top_lvl mono sig_fn prag_fn rec_tc bind_list
= do { ((binds', mono_infos), wanted)
<- captureConstraints $
tcMonoBinds sig_fn LetLclBndr rec_tc bind_list
; unifyCtxts [sig | (_, Just sig, _) <- mono_infos]
; let name_taus = [(name, idType mono_id) | (name, _, mono_id) <- mono_infos]
; (qtvs, givens, ev_binds) <- simplifyInfer top_lvl mono name_taus wanted
; exports <- mapM (mkExport prag_fn qtvs (map evVarPred givens))
mono_infos
; let poly_ids = [poly_id | (_, poly_id, _, _) <- exports]
; traceTc "Binding:" (ppr (poly_ids `zip` map idType poly_ids))
; loc <- getSrcSpanM
; let abs_bind = L loc $ AbsBinds { abs_tvs = qtvs
, abs_ev_vars = givens, abs_ev_binds = ev_binds
, abs_exports = exports, abs_binds = binds' }
; return (unitBag abs_bind, poly_ids)
}
mkExport :: PragFun -> [TyVar] -> TcThetaType
-> MonoBindInfo
-> TcM ([TyVar], Id, Id, TcSpecPrags)
mkExport prag_fn inferred_tvs theta
(poly_name, mb_sig, mono_id)
= do { (tvs, poly_id) <- mk_poly_id mb_sig
; poly_id' <- addInlinePrags poly_id prag_sigs
; spec_prags <- tcSpecPrags poly_id prag_sigs
; return (tvs, poly_id', mono_id, SpecPrags spec_prags) }
where
prag_sigs = prag_fn poly_name
poly_ty = mkSigmaTy inferred_tvs theta (idType mono_id)
mk_poly_id Nothing = do { poly_ty' <- zonkTcTypeCarefully poly_ty
; return (inferred_tvs, mkLocalId poly_name poly_ty') }
mk_poly_id (Just sig) = do { tvs <- mapM zonk_tv (sig_tvs sig)
; return (tvs, sig_id sig) }
zonk_tv tv = do { ty <- zonkTcTyVar tv; return (tcGetTyVar "mkExport" ty) }
type PragFun = Name -> [LSig Name]
mkPragFun :: [LSig Name] -> LHsBinds Name -> PragFun
mkPragFun sigs binds = \n -> lookupNameEnv prag_env n `orElse` []
where
prs = mapCatMaybes get_sig sigs
get_sig :: LSig Name -> Maybe (Located Name, LSig Name)
get_sig (L l (SpecSig nm ty inl)) = Just (nm, L l $ SpecSig nm ty (add_arity nm inl))
get_sig (L l (InlineSig nm inl)) = Just (nm, L l $ InlineSig nm (add_arity nm inl))
get_sig _ = Nothing
add_arity (L _ n) inl_prag
| Just ar <- lookupNameEnv ar_env n,
Inline <- inl_inline inl_prag = inl_prag { inl_sat = Just ar }
| otherwise = inl_prag
prag_env :: NameEnv [LSig Name]
prag_env = foldl add emptyNameEnv prs
add env (L _ n,p) = extendNameEnv_Acc (:) singleton env n p
ar_env :: NameEnv Arity
ar_env = foldrBag lhsBindArity emptyNameEnv binds
lhsBindArity :: LHsBind Name -> NameEnv Arity -> NameEnv Arity
lhsBindArity (L _ (FunBind { fun_id = id, fun_matches = ms })) env
= extendNameEnv env (unLoc id) (matchGroupArity ms)
lhsBindArity _ env = env
tcSpecPrags :: Id -> [LSig Name]
-> TcM [LTcSpecPrag]
tcSpecPrags poly_id prag_sigs
= do { unless (null bad_sigs) warn_discarded_sigs
; mapAndRecoverM (wrapLocM (tcSpec poly_id)) spec_sigs }
where
spec_sigs = filter isSpecLSig prag_sigs
bad_sigs = filter is_bad_sig prag_sigs
is_bad_sig s = not (isSpecLSig s || isInlineLSig s)
warn_discarded_sigs = warnPrags poly_id bad_sigs $
ptext (sLit "Discarding unexpected pragmas for")
tcSpec :: TcId -> Sig Name -> TcM TcSpecPrag
tcSpec poly_id prag@(SpecSig _ hs_ty inl)
= addErrCtxt (spec_ctxt prag) $
do { spec_ty <- tcHsSigType sig_ctxt hs_ty
; warnIf (not (isOverloadedTy poly_ty || isInlinePragma inl))
(ptext (sLit "SPECIALISE pragma for non-overloaded function") <+> quotes (ppr poly_id))
; wrap <- tcSubType origin sig_ctxt (idType poly_id) spec_ty
; return (SpecPrag poly_id wrap inl) }
where
name = idName poly_id
poly_ty = idType poly_id
origin = SpecPragOrigin name
sig_ctxt = FunSigCtxt name
spec_ctxt prag = hang (ptext (sLit "In the SPECIALISE pragma")) 2 (ppr prag)
tcSpec _ prag = pprPanic "tcSpec" (ppr prag)
tcImpPrags :: [LSig Name] -> TcM [LTcSpecPrag]
tcImpPrags prags
= do { this_mod <- getModule
; let is_imp prag
= case sigName prag of
Nothing -> False
Just name -> not (nameIsLocalOrFrom this_mod name)
(spec_prags, others) = partition isSpecLSig $
filter is_imp prags
; mapM_ misplacedSigErr others
; mapAndRecoverM (wrapLocM tcImpSpec) spec_prags }
tcImpSpec :: Sig Name -> TcM TcSpecPrag
tcImpSpec prag@(SpecSig (L _ name) _ _)
= do { id <- tcLookupId name
; checkTc (isAnyInlinePragma (idInlinePragma id))
(impSpecErr name)
; tcSpec id prag }
tcImpSpec p = pprPanic "tcImpSpec" (ppr p)
impSpecErr :: Name -> SDoc
impSpecErr name
= hang (ptext (sLit "You cannot SPECIALISE") <+> quotes (ppr name))
2 (ptext (sLit "because its definition has no INLINE/INLINABLE pragma"))
recoveryCode :: [Name] -> SigFun -> TcM (LHsBinds TcId, [Id])
recoveryCode binder_names sig_fn
= do { traceTc "tcBindsWithSigs: error recovery" (ppr binder_names)
; poly_ids <- mapM mk_dummy binder_names
; return (emptyBag, poly_ids) }
where
mk_dummy name
| isJust (sig_fn name) = tcLookupId name
| otherwise = return (mkLocalId name forall_a_a)
forall_a_a :: TcType
forall_a_a = mkForAllTy openAlphaTyVar (mkTyVarTy openAlphaTyVar)
\end{code}
Note [SPECIALISE pragmas]
~~~~~~~~~~~~~~~~~~~~~~~~~
There is no point in a SPECIALISE pragma for a non-overloaded function:
reverse :: [a] -> [a]
{-# SPECIALISE reverse :: [Int] -> [Int] #-}
But SPECIALISE INLINE *can* make sense for GADTS:
data Arr e where
ArrInt :: !Int -> ByteArray# -> Arr Int
ArrPair :: !Int -> Arr e1 -> Arr e2 -> Arr (e1, e2)
(!:) :: Arr e -> Int -> e
{-# SPECIALISE INLINE (!:) :: Arr Int -> Int -> Int #-}
{-# SPECIALISE INLINE (!:) :: Arr (a, b) -> Int -> (a, b) #-}
(ArrInt _ ba) !: (I# i) = I# (indexIntArray# ba i)
(ArrPair _ a1 a2) !: i = (a1 !: i, a2 !: i)
When (!:) is specialised it becomes non-recursive, and can usefully
be inlined. Scary! So we only warn for SPECIALISE *without* INLINE
for a non-overloaded function.
%************************************************************************
%* *
\subsection{tcMonoBind}
%* *
%************************************************************************
@tcMonoBinds@ deals with a perhaps-recursive group of HsBinds.
The signatures have been dealt with already.
\begin{code}
tcMonoBinds :: TcSigFun -> LetBndrSpec
-> RecFlag
-> [LHsBind Name]
-> TcM (LHsBinds TcId, [MonoBindInfo])
tcMonoBinds sig_fn no_gen is_rec
[ L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf,
fun_matches = matches, bind_fvs = fvs })]
| NonRecursive <- is_rec
, Nothing <- sig_fn name
=
setSrcSpan b_loc $
do { ((co_fn, matches'), rhs_ty) <- tcInfer (tcMatchesFun name inf matches)
; mono_id <- newNoSigLetBndr no_gen name rhs_ty
; return (unitBag (L b_loc (FunBind { fun_id = L nm_loc mono_id, fun_infix = inf,
fun_matches = matches', bind_fvs = fvs,
fun_co_fn = co_fn, fun_tick = Nothing })),
[(name, Nothing, mono_id)]) }
tcMonoBinds sig_fn no_gen _ binds
= do { tc_binds <- mapM (wrapLocM (tcLhs sig_fn no_gen)) binds
; let mono_info = getMonoBindInfo tc_binds
rhs_id_env = [(name,mono_id) | (name, Nothing, mono_id) <- mono_info]
; binds' <- tcExtendIdEnv2 rhs_id_env $ do
traceTc "tcMonoBinds" $ vcat [ ppr n <+> ppr id <+> ppr (idType id)
| (n,id) <- rhs_id_env]
mapM (wrapLocM tcRhs) tc_binds
; return (listToBag binds', mono_info) }
data TcMonoBind
= TcFunBind MonoBindInfo SrcSpan Bool (MatchGroup Name)
| TcPatBind [MonoBindInfo] (LPat TcId) (GRHSs Name) TcSigmaType
type MonoBindInfo = (Name, Maybe TcSigInfo, TcId)
tcLhs :: TcSigFun -> LetBndrSpec -> HsBind Name -> TcM TcMonoBind
tcLhs sig_fn no_gen (FunBind { fun_id = L nm_loc name, fun_infix = inf, fun_matches = matches })
| Just sig <- sig_fn name
= do { mono_id <- newSigLetBndr no_gen name sig
; return (TcFunBind (name, Just sig, mono_id) nm_loc inf matches) }
| otherwise
= do { mono_ty <- newFlexiTyVarTy argTypeKind
; mono_id <- newNoSigLetBndr no_gen name mono_ty
; return (TcFunBind (name, Nothing, mono_id) nm_loc inf matches) }
tcLhs sig_fn no_gen (PatBind { pat_lhs = pat, pat_rhs = grhss })
= do { let tc_pat exp_ty = tcLetPat sig_fn no_gen pat exp_ty $
mapM lookup_info (collectPatBinders pat)
lookup_info :: Name -> TcM MonoBindInfo
lookup_info name = do { mono_id <- tcLookupId name
; return (name, sig_fn name, mono_id) }
; ((pat', infos), pat_ty) <- addErrCtxt (patMonoBindsCtxt pat grhss) $
tcInfer tc_pat
; return (TcPatBind infos pat' grhss pat_ty) }
tcLhs _ _ other_bind = pprPanic "tcLhs" (ppr other_bind)
tcRhs :: TcMonoBind -> TcM (HsBind TcId)
tcRhs (TcFunBind (_,_,mono_id) loc inf matches)
= do { (co_fn, matches') <- tcMatchesFun (idName mono_id) inf
matches (idType mono_id)
; return (FunBind { fun_id = L loc mono_id, fun_infix = inf
, fun_matches = matches'
, fun_co_fn = co_fn
, bind_fvs = placeHolderNames, fun_tick = Nothing }) }
tcRhs (TcPatBind _ pat' grhss pat_ty)
= do { grhss' <- addErrCtxt (patMonoBindsCtxt pat' grhss) $
tcGRHSsPat grhss pat_ty
; return (PatBind { pat_lhs = pat', pat_rhs = grhss', pat_rhs_ty = pat_ty
, bind_fvs = placeHolderNames }) }
getMonoBindInfo :: [Located TcMonoBind] -> [MonoBindInfo]
getMonoBindInfo tc_binds
= foldr (get_info . unLoc) [] tc_binds
where
get_info (TcFunBind info _ _ _) rest = info : rest
get_info (TcPatBind infos _ _ _) rest = infos ++ rest
\end{code}
%************************************************************************
%* *
Generalisation
%* *
%************************************************************************
unifyCtxts checks that all the signature contexts are the same
The type signatures on a mutually-recursive group of definitions
must all have the same context (or none).
The trick here is that all the signatures should have the same
context, and we want to share type variables for that context, so that
all the right hand sides agree a common vocabulary for their type
constraints
We unify them because, with polymorphic recursion, their types
might not otherwise be related. This is a rather subtle issue.
\begin{code}
unifyCtxts :: [TcSigInfo] -> TcM ()
unifyCtxts [] = return ()
unifyCtxts (sig1 : sigs)
= do { traceTc "unifyCtxts" (ppr (sig1 : sigs))
; mapM_ unify_ctxt sigs }
where
theta1 = sig_theta sig1
unify_ctxt :: TcSigInfo -> TcM ()
unify_ctxt sig@(TcSigInfo { sig_theta = theta })
= setSrcSpan (sig_loc sig) $
addErrCtxt (sigContextsCtxt sig1 sig) $
do { cois <- unifyTheta theta1 theta
;
checkTc (all isIdentityCoI cois)
(ptext (sLit "Mutually dependent functions have syntactically distinct contexts"))
}
\end{code}
@getTyVarsToGen@ decides what type variables to generalise over.
For a "restricted group" -- see the monomorphism restriction
for a definition -- we bind no dictionaries, and
remove from tyvars_to_gen any constrained type variables
*Don't* simplify dicts at this point, because we aren't going
to generalise over these dicts. By the time we do simplify them
we may well know more. For example (this actually came up)
f :: Array Int Int
f x = array ... xs where xs = [1,2,3,4,5]
We don't want to generate lots of (fromInt Int 1), (fromInt Int 2)
stuff. If we simplify only at the f-binding (not the xs-binding)
we'll know that the literals are all Ints, and we can just produce
Int literals!
Find all the type variables involved in overloading, the
"constrained_tyvars". These are the ones we *aren't* going to
generalise. We must be careful about doing this:
(a) If we fail to generalise a tyvar which is not actually
constrained, then it will never, ever get bound, and lands
up printed out in interface files! Notorious example:
instance Eq a => Eq (Foo a b) where ..
Here, b is not constrained, even though it looks as if it is.
Another, more common, example is when there's a Method inst in
the LIE, whose type might very well involve non-overloaded
type variables.
[NOTE: Jan 2001: I don't understand the problem here so I'm doing
the simple thing instead]
(b) On the other hand, we mustn't generalise tyvars which are constrained,
because we are going to pass on out the unmodified LIE, with those
tyvars in it. They won't be in scope if we've generalised them.
So we are careful, and do a complete simplification just to find the
constrained tyvars. We don't use any of the results, except to
find which tyvars are constrained.
Note [Polymorphic recursion]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The game plan for polymorphic recursion in the code above is
* Bind any variable for which we have a type signature
to an Id with a polymorphic type. Then when type-checking
the RHSs we'll make a full polymorphic call.
This fine, but if you aren't a bit careful you end up with a horrendous
amount of partial application and (worse) a huge space leak. For example:
f :: Eq a => [a] -> [a]
f xs = ...f...
If we don't take care, after typechecking we get
f = /\a -> \d::Eq a -> let f' = f a d
in
\ys:[a] -> ...f'...
Notice the the stupid construction of (f a d), which is of course
identical to the function we're executing. In this case, the
polymorphic recursion isn't being used (but that's a very common case).
This can lead to a massive space leak, from the following top-level defn
(post-typechecking)
ff :: [Int] -> [Int]
ff = f Int dEqInt
Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but
f' is another thunk which evaluates to the same thing... and you end
up with a chain of identical values all hung onto by the CAF ff.
ff = f Int dEqInt
= let f' = f Int dEqInt in \ys. ...f'...
= let f' = let f' = f Int dEqInt in \ys. ...f'...
in \ys. ...f'...
Etc.
NOTE: a bit of arity anaysis would push the (f a d) inside the (\ys...),
which would make the space leak go away in this case
Solution: when typechecking the RHSs we always have in hand the
*monomorphic* Ids for each binding. So we just need to make sure that
if (Method f a d) shows up in the constraints emerging from (...f...)
we just use the monomorphic Id. We achieve this by adding monomorphic Ids
to the "givens" when simplifying constraints. That's what the "lies_avail"
is doing.
Then we get
f = /\a -> \d::Eq a -> letrec
fm = \ys:[a] -> ...fm...
in
fm
%************************************************************************
%* *
Signatures
%* *
%************************************************************************
Type signatures are tricky. See Note [Signature skolems] in TcType
@tcSigs@ checks the signatures for validity, and returns a list of
{\em freshly-instantiated} signatures. That is, the types are already
split up, and have fresh type variables installed. All non-type-signature
"RenamedSigs" are ignored.
The @TcSigInfo@ contains @TcTypes@ because they are unified with
the variable's type, and after that checked to see whether they've
been instantiated.
Note [Scoped tyvars]
~~~~~~~~~~~~~~~~~~~~
The -XScopedTypeVariables flag brings lexically-scoped type variables
into scope for any explicitly forall-quantified type variables:
f :: forall a. a -> a
f x = e
Then 'a' is in scope inside 'e'.
However, we do *not* support this
- For pattern bindings e.g
f :: forall a. a->a
(f,g) = e
- For multiple function bindings, unless Opt_RelaxedPolyRec is on
f :: forall a. a -> a
f = g
g :: forall b. b -> b
g = ...f...
Reason: we use mutable variables for 'a' and 'b', since they may
unify to each other, and that means the scoped type variable would
not stand for a completely rigid variable.
Currently, we simply make Opt_ScopedTypeVariables imply Opt_RelaxedPolyRec
Note [More instantiated than scoped]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
There may be more instantiated type variables than lexically-scoped
ones. For example:
type T a = forall b. b -> (a,b)
f :: forall c. T c
Here, the signature for f will have one scoped type variable, c,
but two instantiated type variables, c' and b'.
We assume that the scoped ones are at the *front* of sig_tvs,
and remember the names from the original HsForAllTy in the TcSigFun.
Note [Signature skolems]
~~~~~~~~~~~~~~~~~~~~~~~~
When instantiating a type signature, we do so with either skolems or
SigTv meta-type variables depending on the use_skols boolean. This
variable is set True when we are typechecking a single function
binding; and False for pattern bindings and a group of several
function bindings.
Reason: in the latter cases, the "skolems" can be unified together,
so they aren't properly rigid in the type-refinement sense.
NB: unless we are doing H98, each function with a sig will be done
separately, even if it's mutually recursive, so use_skols will be True
Note [Only scoped tyvars are in the TyVarEnv]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We are careful to keep only the *lexically scoped* type variables in
the type environment. Why? After all, the renamer has ensured
that only legal occurrences occur, so we could put all type variables
into the type env.
But we want to check that two distinct lexically scoped type variables
do not map to the same internal type variable. So we need to know which
the lexically-scoped ones are... and at the moment we do that by putting
only the lexically scoped ones into the environment.
Note [Instantiate sig with fresh variables]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
It's vital to instantiate a type signature with fresh variables.
For example:
type T = forall a. [a] -> [a]
f :: T;
f = g where { g :: T; g = }
We must not use the same 'a' from the defn of T at both places!!
(Instantiation is only necessary because of type synonyms. Otherwise,
it's all cool; each signature has distinct type variables from the renamer.)
\begin{code}
type SigFun = Name -> Maybe ([Name], SrcSpan)
mkSigFun :: [LSig Name] -> SigFun
mkSigFun sigs = lookupNameEnv env
where
env = mkNameEnv (mapCatMaybes mk_pair sigs)
mk_pair (L loc (TypeSig (L _ name) lhs_ty)) = Just (name, (hsExplicitTvs lhs_ty, loc))
mk_pair (L loc (IdSig id)) = Just (idName id, ([], loc))
mk_pair _ = Nothing
\end{code}
\begin{code}
tcTySig :: LSig Name -> TcM TcId
tcTySig (L span (TypeSig (L _ name) ty))
= setSrcSpan span $
do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
; return (mkLocalId name sigma_ty) }
tcTySig (L _ (IdSig id))
= return id
tcTySig s = pprPanic "tcTySig" (ppr s)
tcInstSigs :: SigFun -> [Name] -> TcM TcSigFun
tcInstSigs sig_fn bndrs
= do { prs <- mapMaybeM (tcInstSig sig_fn use_skols) bndrs
; return (lookupNameEnv (mkNameEnv prs)) }
where
use_skols = isSingleton bndrs
tcInstSig :: SigFun -> Bool -> Name -> TcM (Maybe (Name, TcSigInfo))
tcInstSig sig_fn use_skols name
| Just (scoped_tvs, loc) <- sig_fn name
= do { poly_id <- tcLookupId name
; let poly_ty = idType poly_id
; (tvs, theta, tau) <- if use_skols
then tcInstType tcInstSkolTyVars poly_ty
else tcInstType tcInstSigTyVars poly_ty
; let sig = TcSigInfo { sig_id = poly_id
, sig_scoped = scoped_tvs
, sig_tvs = tvs, sig_theta = theta, sig_tau = tau
, sig_loc = loc }
; return (Just (name, sig)) }
| otherwise
= return Nothing
data GeneralisationPlan
= NoGen
| InferGen Bool
| CheckGen TcSigInfo
instance Outputable GeneralisationPlan where
ppr NoGen = ptext (sLit "NoGen")
ppr (InferGen b) = ptext (sLit "InferGen") <+> ppr b
ppr (CheckGen s) = ptext (sLit "CheckGen") <+> ppr s
decideGeneralisationPlan
:: DynFlags -> TopLevelFlag -> [Name] -> [LHsBind Name] -> TcSigFun -> GeneralisationPlan
decideGeneralisationPlan dflags top_lvl _bndrs binds sig_fn
| bang_pat_binds = NoGen
| mono_pat_binds = NoGen
| Just sig <- one_funbind_with_sig binds = if null (sig_tvs sig) && null (sig_theta sig)
then NoGen
else CheckGen sig
| (xopt Opt_MonoLocalBinds dflags
&& isNotTopLevel top_lvl) = NoGen
| otherwise = InferGen mono_restriction
where
bang_pat_binds = any (isBangHsBind . unLoc) binds
mono_pat_binds = xopt Opt_MonoPatBinds dflags
&& any (is_pat_bind . unLoc) binds
mono_restriction = xopt Opt_MonomorphismRestriction dflags
&& any (restricted . unLoc) binds
no_sig n = isNothing (sig_fn n)
one_funbind_with_sig [L _ FunBind { fun_id = v }] = sig_fn (unLoc v)
one_funbind_with_sig _ = Nothing
restricted (PatBind {}) = True
restricted (VarBind { var_id = v }) = no_sig v
restricted (FunBind { fun_id = v, fun_matches = m }) = restricted_match m
&& no_sig (unLoc v)
restricted (AbsBinds {}) = panic "isRestrictedGroup/unrestricted AbsBinds"
restricted_match (MatchGroup (L _ (Match [] _ _) : _) _) = True
restricted_match _ = False
is_pat_bind (PatBind {}) = True
is_pat_bind _ = False
checkStrictBinds :: TopLevelFlag -> RecFlag
-> [LHsBind Name] -> [Id]
-> TcM ()
checkStrictBinds top_lvl rec_group binds poly_ids
| unlifted || bang_pat
= do { checkTc (isNotTopLevel top_lvl)
(strictBindErr "Top-level" unlifted binds)
; checkTc (isNonRec rec_group)
(strictBindErr "Recursive" unlifted binds)
; checkTc (isSingleton binds)
(strictBindErr "Multiple" unlifted binds)
; warnUnlifted <- doptM Opt_WarnLazyUnliftedBindings
; warnTc (warnUnlifted && not bang_pat)
(unliftedMustBeBang binds) }
| otherwise
= return ()
where
unlifted = any is_unlifted poly_ids
bang_pat = any (isBangHsBind . unLoc) binds
is_unlifted id = case tcSplitForAllTys (idType id) of
(_, rho) -> isUnLiftedType rho
unliftedMustBeBang :: [LHsBind Name] -> SDoc
unliftedMustBeBang binds
= hang (text "Bindings containing unlifted types should use an outermost bang pattern:")
2 (pprBindList binds)
strictBindErr :: String -> Bool -> [LHsBind Name] -> SDoc
strictBindErr flavour unlifted binds
= hang (text flavour <+> msg <+> ptext (sLit "aren't allowed:"))
2 (pprBindList binds)
where
msg | unlifted = ptext (sLit "bindings for unlifted types")
| otherwise = ptext (sLit "bang-pattern bindings")
pprBindList :: [LHsBind Name] -> SDoc
pprBindList binds = vcat (map ppr binds)
\end{code}
%************************************************************************
%* *
\subsection[TcBinds-errors]{Error contexts and messages}
%* *
%************************************************************************
\begin{code}
patMonoBindsCtxt :: OutputableBndr id => LPat id -> GRHSs Name -> SDoc
patMonoBindsCtxt pat grhss
= hang (ptext (sLit "In a pattern binding:")) 2 (pprPatBind pat grhss)
sigContextsCtxt :: TcSigInfo -> TcSigInfo -> SDoc
sigContextsCtxt sig1 sig2
= vcat [ptext (sLit "When matching the contexts of the signatures for"),
nest 2 (vcat [ppr id1 <+> dcolon <+> ppr (idType id1),
ppr id2 <+> dcolon <+> ppr (idType id2)]),
ptext (sLit "The signature contexts in a mutually recursive group should all be identical")]
where
id1 = sig_id sig1
id2 = sig_id sig2
\end{code}