%
-% (c) The GRASP/AQUA Project, Glasgow University, 1992-1995
+% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
\section[TcBinds]{TcBinds}
\begin{code}
-#include "HsVersions.h"
-
-module TcBinds (
- tcTopBindsAndThen, tcLocalBindsAndThen,
- tcSigs, doSpecPragma
- ) where
-
---IMPORT_Trace -- ToDo:rm (debugging)
+module TcBinds ( tcLocalBinds, tcTopBinds,
+ tcHsBootSigs, tcMonoBinds,
+ TcPragFun, tcSpecPrag, tcPrags, mkPragFun,
+ TcSigInfo(..),
+ badBootDeclErr ) where
-import TcMonad -- typechecking monad machinery
-import TcMonadFns ( newLocalsWithOpenTyVarTys,
- newLocalsWithPolyTyVarTys,
- newSpecPragmaId, newSpecId,
- applyTcSubstAndCollectTyVars
- )
-import AbsSyn -- the stuff being typechecked
+#include "HsVersions.h"
-import AbsUniType ( isTyVarTy, isGroundTy, isUnboxedDataType,
- isGroundOrTyVarTy, extractTyVarsFromTy,
- UniType
- )
-import BackSubst ( applyTcSubstToBinds )
-import E
-import Errors ( topLevelUnboxedDeclErr, specGroundnessErr,
- specCtxtGroundnessErr, Error(..), UnifyErrContext(..)
+import {-# SOURCE #-} TcMatches ( tcGRHSsPat, tcMatchesFun )
+import {-# SOURCE #-} TcExpr ( tcMonoExpr )
+
+import DynFlags ( DynFlag(Opt_MonomorphismRestriction, Opt_GlasgowExts) )
+import HsSyn ( HsExpr(..), HsBind(..), LHsBinds, LHsBind, Sig(..),
+ HsLocalBinds(..), HsValBinds(..), HsIPBinds(..),
+ LSig, Match(..), IPBind(..), Prag(..),
+ HsType(..), LHsType, HsExplicitForAll(..), hsLTyVarNames,
+ isVanillaLSig, sigName, placeHolderNames, isPragLSig,
+ LPat, GRHSs, MatchGroup(..), pprLHsBinds, mkHsCoerce,
+ collectHsBindBinders, collectPatBinders, pprPatBind, isBangHsBind
)
-import GenSpecEtc ( checkSigTyVars, genBinds, SignatureInfo(..) )
-import Id ( getIdUniType, mkInstId )
-import IdInfo ( SpecInfo(..) )
-import Inst
-import LIE ( nullLIE, mkLIE, plusLIE, LIE )
-import Maybes ( assocMaybe, catMaybes, Maybe(..) )
-import Spec ( specTy )
-import TVE ( nullTVE, TVE(..), UniqFM )
-import TcMonoBnds ( tcMonoBinds )
-import TcPolyType ( tcPolyType )
+import TcHsSyn ( zonkId )
+
+import TcRnMonad
+import Inst ( newDictsAtLoc, newIPDict, instToId )
+import TcEnv ( tcExtendIdEnv, tcExtendIdEnv2, tcExtendTyVarEnv2,
+ pprBinders, tcLookupLocalId_maybe, tcLookupId,
+ tcGetGlobalTyVars )
+import TcUnify ( tcInfer, tcSubExp, unifyTheta,
+ bleatEscapedTvs, sigCtxt )
+import TcSimplify ( tcSimplifyInfer, tcSimplifyInferCheck,
+ tcSimplifyRestricted, tcSimplifyIPs )
+import TcHsType ( tcHsSigType, UserTypeCtxt(..) )
+import TcPat ( tcPat, PatCtxt(..) )
import TcSimplify ( bindInstsOfLocalFuns )
-import Unify ( unifyTauTy )
-import UniqFM ( emptyUFM ) -- profiling, pragmas only
-import Util
+import TcMType ( newFlexiTyVarTy, zonkQuantifiedTyVar, zonkSigTyVar,
+ tcInstSigTyVars, tcInstSkolTyVars, tcInstType,
+ zonkTcType, zonkTcTypes, zonkTcTyVars )
+import TcType ( TcType, TcTyVar, TcThetaType,
+ SkolemInfo(SigSkol), UserTypeCtxt(FunSigCtxt),
+ TcTauType, TcSigmaType, isUnboxedTupleType,
+ mkTyVarTy, mkForAllTys, mkFunTys, exactTyVarsOfType,
+ mkForAllTy, isUnLiftedType, tcGetTyVar,
+ mkTyVarTys, tidyOpenTyVar )
+import Kind ( argTypeKind )
+import VarEnv ( TyVarEnv, emptyVarEnv, lookupVarEnv, extendVarEnv )
+import TysWiredIn ( unitTy )
+import TysPrim ( alphaTyVar )
+import Id ( Id, mkLocalId, mkVanillaGlobal )
+import IdInfo ( vanillaIdInfo )
+import Var ( TyVar, idType, idName )
+import Name ( Name )
+import NameSet
+import NameEnv
+import VarSet
+import SrcLoc ( Located(..), unLoc, getLoc )
+import Bag
+import ErrUtils ( Message )
+import Digraph ( SCC(..), stronglyConnComp )
+import Maybes ( expectJust, isJust, isNothing, orElse )
+import Util ( singleton )
+import BasicTypes ( TopLevelFlag(..), isTopLevel, isNotTopLevel,
+ RecFlag(..), isNonRec, InlineSpec, defaultInlineSpec )
+import Outputable
\end{code}
-%************************************************************************
-%* *
-\subsection{Type-checking top-level bindings}
-%* *
-%************************************************************************
-
-@tcBindsAndThen@ takes a boolean which indicates whether the binding
-group is at top level or not. The difference from inner bindings is
-that
-\begin{enumerate}
-\item
-we zero the substitution before each group
-\item
-we back-substitute after each group.
-\end{enumerate}
-We still return an LIE, but it is sure to contain nothing but constant
-dictionaries, which we resolve at the module level.
-
-@tcTopBinds@ returns an LVE, not, as you might expect, a GVE. Why?
-Because the monomorphism restriction means that is might return some
-monomorphic things, with free type variables. Hence it must be an LVE.
-
-The LIE returned by @tcTopBinds@ may constrain some type variables,
-but they are guaranteed to be a subset of those free in the
-corresponding returned LVE.
%************************************************************************
%* *
%* *
%************************************************************************
-@tcBindsAndThen@ typechecks a @Binds@. The "and then" part is because
+@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
@tcBindsAndThen@ also takes a "combiner" which glues together the
bindings and the "thing" to make a new "thing".
-The real work is done by @tcBindAndThen@.
+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
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}
-tcBindsAndThen
- :: Bool
- -> E
- -> (TypecheckedBinds -> thing -> thing) -- Combinator
- -> RenamedBinds
- -> (E -> TcM (thing, LIE, thing_ty))
- -> TcM (thing, LIE, thing_ty)
-
-tcBindsAndThen top_level e combiner EmptyBinds do_next
- = do_next e `thenTc` \ (thing, lie, thing_ty) ->
- returnTc (combiner EmptyBinds thing, lie, thing_ty)
-
-tcBindsAndThen top_level e combiner (SingleBind bind) do_next
- = tcBindAndThen top_level e combiner bind [] do_next
-
-tcBindsAndThen top_level e combiner (BindWith bind sigs) do_next
- = tcBindAndThen top_level e combiner bind sigs do_next
-
-tcBindsAndThen top_level e combiner (ThenBinds binds1 binds2) do_next
- = tcBindsAndThen top_level e combiner binds1 new_after
+tcTopBinds :: HsValBinds Name -> TcM (LHsBinds TcId, TcLclEnv)
+ -- Note: returning the TcLclEnv is more than we really
+ -- want. The bit we care about is the local bindings
+ -- and the free type variables thereof
+tcTopBinds binds
+ = do { (ValBindsOut prs _, env) <- tcValBinds TopLevel binds getLclEnv
+ ; return (foldr (unionBags . snd) emptyBag prs, env) }
+ -- The top level bindings are flattened into a giant
+ -- implicitly-mutually-recursive LHsBinds
+
+tcHsBootSigs :: HsValBinds Name -> TcM [Id]
+-- A hs-boot file has only one BindGroup, and it only has type
+-- signatures in it. The renamer checked all this
+tcHsBootSigs (ValBindsOut binds sigs)
+ = do { checkTc (null binds) badBootDeclErr
+ ; mapM (addLocM tc_boot_sig) (filter isVanillaLSig sigs) }
+ where
+ tc_boot_sig (TypeSig (L _ name) ty)
+ = do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty
+ ; return (mkVanillaGlobal name sigma_ty vanillaIdInfo) }
+ -- Notice that we make GlobalIds, not LocalIds
+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 { (thing, lie) <- getLIE thing_inside
+ ; (avail_ips, ip_binds') <- mapAndUnzipM (wrapLocSndM tc_ip_bind) ip_binds
+
+ -- If the binding binds ?x = E, we must now
+ -- discharge any ?x constraints in expr_lie
+ ; dict_binds <- tcSimplifyIPs avail_ips lie
+ ; return (HsIPBinds (IPBinds ip_binds' dict_binds), thing) }
+ where
+ -- I wonder if we should do these one at at time
+ -- Consider ?x = 4
+ -- ?y = ?x + 1
+ tc_ip_bind (IPBind ip expr)
+ = newFlexiTyVarTy argTypeKind `thenM` \ ty ->
+ newIPDict (IPBindOrigin ip) ip ty `thenM` \ (ip', ip_inst) ->
+ tcMonoExpr expr ty `thenM` \ expr' ->
+ returnM (ip_inst, (IPBind ip' expr'))
+
+------------------------
+tcValBinds :: TopLevelFlag
+ -> HsValBinds Name -> TcM thing
+ -> TcM (HsValBinds TcId, thing)
+
+tcValBinds top_lvl (ValBindsIn binds sigs) thing_inside
+ = pprPanic "tcValBinds" (ppr binds)
+
+tcValBinds top_lvl (ValBindsOut binds sigs) thing_inside
+ = do { -- Typecheck the signature
+ ; let { prag_fn = mkPragFun sigs
+ ; ty_sigs = filter isVanillaLSig sigs
+ ; sig_fn = mkSigFun ty_sigs }
+
+ ; poly_ids <- mapM tcTySig ty_sigs
+
+ -- Extend the envt right away with all
+ -- the Ids declared with type signatures
+ ; (binds', thing) <- tcExtendIdEnv poly_ids $
+ tc_val_binds top_lvl sig_fn prag_fn
+ binds thing_inside
+
+ ; return (ValBindsOut binds' sigs, thing) }
+
+------------------------
+tc_val_binds :: TopLevelFlag -> TcSigFun -> TcPragFun
+ -> [(RecFlag, LHsBinds Name)] -> TcM thing
+ -> TcM ([(RecFlag, LHsBinds TcId)], thing)
+-- Typecheck a whole lot of value bindings,
+-- one strongly-connected component at a time
+
+tc_val_binds top_lvl sig_fn prag_fn [] thing_inside
+ = do { thing <- thing_inside
+ ; return ([], thing) }
+
+tc_val_binds top_lvl sig_fn prag_fn (group : groups) thing_inside
+ = do { (group', (groups', thing))
+ <- tc_group top_lvl sig_fn prag_fn group $
+ tc_val_binds top_lvl sig_fn prag_fn groups thing_inside
+ ; return (group' ++ groups', thing) }
+
+------------------------
+tc_group :: TopLevelFlag -> TcSigFun -> TcPragFun
+ -> (RecFlag, LHsBinds Name) -> TcM thing
+ -> TcM ([(RecFlag, LHsBinds TcId)], thing)
+
+-- Typecheck one strongly-connected component of the original program.
+-- We get a list of groups back, because there may
+-- be specialisations etc as well
+
+tc_group top_lvl sig_fn prag_fn (NonRecursive, binds) thing_inside
+ = -- A single non-recursive binding
+ -- We want to keep non-recursive things non-recursive
+ -- so that we desugar unlifted bindings correctly
+ do { (binds, thing) <- tcPolyBinds top_lvl NonRecursive NonRecursive
+ sig_fn prag_fn binds thing_inside
+ ; return ([(NonRecursive, b) | b <- binds], thing) }
+
+tc_group top_lvl sig_fn prag_fn (Recursive, binds) thing_inside
+ = -- A recursive strongly-connected component
+ -- To maximise polymorphism (with -fglasgow-exts), we do a new
+ -- strongly-connected-component analysis, this time omitting
+ -- any references to variables with type signatures.
+ --
+ -- Then we bring into scope all the variables with type signatures
+ do { traceTc (text "tc_group rec" <+> pprLHsBinds binds)
+ ; gla_exts <- doptM Opt_GlasgowExts
+ ; (binds,thing) <- if gla_exts
+ then go new_sccs
+ else tc_binds Recursive binds thing_inside
+ ; return ([(Recursive, unionManyBags binds)], thing) }
+ -- Rec them all together
+ where
+ new_sccs :: [SCC (LHsBind Name)]
+ new_sccs = stronglyConnComp (mkEdges sig_fn binds)
+
+-- go :: SCC (LHsBind Name) -> TcM ([LHsBind TcId], thing)
+ go (scc:sccs) = do { (binds1, (binds2, thing)) <- go1 scc (go sccs)
+ ; return (binds1 ++ binds2, thing) }
+ go [] = do { thing <- thing_inside; return ([], thing) }
+
+ go1 (AcyclicSCC bind) = tc_binds NonRecursive (unitBag bind)
+ go1 (CyclicSCC binds) = tc_binds Recursive (listToBag binds)
+
+ tc_binds rec_tc binds = tcPolyBinds top_lvl Recursive rec_tc sig_fn prag_fn binds
+
+------------------------
+mkEdges :: TcSigFun -> LHsBinds Name
+ -> [(LHsBind Name, BKey, [BKey])]
+
+type BKey = Int -- Just number off the bindings
+
+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 -- Which binding it comes from
+ 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]
+
+------------------------
+tcPolyBinds :: TopLevelFlag
+ -> RecFlag -- Whether the group is really recursive
+ -> RecFlag -- Whether it's recursive for typechecking purposes
+ -> TcSigFun -> TcPragFun
+ -> LHsBinds Name
+ -> TcM thing
+ -> TcM ([LHsBinds TcId], thing)
+
+-- Typechecks a single bunch of bindings all together,
+-- and generalises them. The bunch may be only part of a recursive
+-- group, because we use type signatures to maximise polymorphism
+--
+-- Deals with the bindInstsOfLocalFuns thing too
+--
+-- Returns a list because the input may be a single non-recursive binding,
+-- in which case the dependency order of the resulting bindings is
+-- important.
+
+tcPolyBinds top_lvl rec_group rec_tc sig_fn prag_fn scc thing_inside
+ = -- NB: polymorphic recursion means that a function
+ -- may use an instance of itself, we must look at the LIE arising
+ -- from the function's own right hand side. Hence the getLIE
+ -- encloses the tc_poly_binds.
+ do { traceTc (text "tcPolyBinds" <+> ppr scc)
+ ; ((binds1, poly_ids, thing), lie) <- getLIE $
+ do { (binds1, poly_ids) <- tc_poly_binds top_lvl rec_group rec_tc
+ sig_fn prag_fn scc
+ ; thing <- tcExtendIdEnv poly_ids thing_inside
+ ; return (binds1, poly_ids, thing) }
+
+ ; if isTopLevel top_lvl
+ then -- For the top level don't bother will all this
+ -- bindInstsOfLocalFuns stuff. All the top level
+ -- things are rec'd together anyway, so it's fine to
+ -- leave them to the tcSimplifyTop,
+ -- and quite a bit faster too
+ do { extendLIEs lie; return (binds1, thing) }
+
+ else do -- Nested case
+ { lie_binds <- bindInstsOfLocalFuns lie poly_ids
+ ; return (binds1 ++ [lie_binds], thing) }}
+
+------------------------
+tc_poly_binds :: TopLevelFlag -- See comments on tcPolyBinds
+ -> RecFlag -> RecFlag
+ -> TcSigFun -> TcPragFun
+ -> LHsBinds Name
+ -> TcM ([LHsBinds TcId], [TcId])
+-- Typechecks the bindings themselves
+-- Knows nothing about the scope of the bindings
+
+tc_poly_binds top_lvl rec_group rec_tc sig_fn prag_fn binds
+ = let
+ binder_names = collectHsBindBinders binds
+ bind_list = bagToList binds
+
+ loc = getLoc (head bind_list)
+ -- TODO: location a bit awkward, but the mbinds have been
+ -- dependency analysed and may no longer be adjacent
+ in
+ -- SET UP THE MAIN RECOVERY; take advantage of any type sigs
+ setSrcSpan loc $
+ recoverM (recoveryCode binder_names) $ do
+
+ { traceTc (ptext SLIT("------------------------------------------------"))
+ ; traceTc (ptext SLIT("Bindings for") <+> ppr binder_names)
+
+ -- TYPECHECK THE BINDINGS
+ ; ((binds', mono_bind_infos), lie_req)
+ <- getLIE (tcMonoBinds bind_list sig_fn rec_tc)
+
+ -- CHECK FOR UNLIFTED BINDINGS
+ -- These must be non-recursive etc, and are not generalised
+ -- They desugar to a case expression in the end
+ ; zonked_mono_tys <- zonkTcTypes (map getMonoType mono_bind_infos)
+ ; is_strict <- checkStrictBinds top_lvl rec_group binds'
+ zonked_mono_tys mono_bind_infos
+ ; if is_strict then
+ do { extendLIEs lie_req
+ ; let exports = zipWith mk_export mono_bind_infos zonked_mono_tys
+ mk_export (name, Nothing, mono_id) mono_ty = ([], mkLocalId name mono_ty, mono_id, [])
+ mk_export (name, Just sig, mono_id) mono_ty = ([], sig_id sig, mono_id, [])
+ -- ToDo: prags for unlifted bindings
+
+ ; return ( [unitBag $ L loc $ AbsBinds [] [] exports binds'],
+ [poly_id | (_, poly_id, _, _) <- exports]) } -- Guaranteed zonked
+
+ else do -- The normal lifted case: GENERALISE
+ { is_unres <- isUnRestrictedGroup bind_list sig_fn
+ ; (tyvars_to_gen, dict_binds, dict_ids)
+ <- addErrCtxt (genCtxt (bndrNames mono_bind_infos)) $
+ generalise top_lvl is_unres mono_bind_infos lie_req
+
+ -- FINALISE THE QUANTIFIED TYPE VARIABLES
+ -- The quantified type variables often include meta type variables
+ -- we want to freeze them into ordinary type variables, and
+ -- default their kind (e.g. from OpenTypeKind to TypeKind)
+ ; tyvars_to_gen' <- mappM zonkQuantifiedTyVar tyvars_to_gen
+
+ -- BUILD THE POLYMORPHIC RESULT IDs
+ ; exports <- mapM (mkExport prag_fn tyvars_to_gen' (map idType dict_ids))
+ mono_bind_infos
+
+ -- ZONK THE poly_ids, because they are used to extend the type
+ -- environment; see the invariant on TcEnv.tcExtendIdEnv
+ ; let poly_ids = [poly_id | (_, poly_id, _, _) <- exports]
+ ; zonked_poly_ids <- mappM zonkId poly_ids
+
+ ; traceTc (text "binding:" <+> ppr (zonked_poly_ids `zip` map idType zonked_poly_ids))
+
+ ; let abs_bind = L loc $ AbsBinds tyvars_to_gen'
+ dict_ids exports
+ (dict_binds `unionBags` binds')
+
+ ; return ([unitBag abs_bind], zonked_poly_ids)
+ } }
+
+
+--------------
+mkExport :: TcPragFun -> [TyVar] -> [TcType] -> MonoBindInfo
+ -> TcM ([TyVar], Id, Id, [Prag])
+mkExport prag_fn inferred_tvs dict_tys (poly_name, mb_sig, mono_id)
+ = case mb_sig of
+ Nothing -> do { prags <- tcPrags poly_id (prag_fn poly_name)
+ ; return (inferred_tvs, poly_id, mono_id, prags) }
+ where
+ poly_id = mkLocalId poly_name poly_ty
+ poly_ty = mkForAllTys inferred_tvs
+ $ mkFunTys dict_tys
+ $ idType mono_id
+
+ Just sig -> do { let poly_id = sig_id sig
+ ; prags <- tcPrags poly_id (prag_fn poly_name)
+ ; sig_tys <- zonkTcTyVars (sig_tvs sig)
+ ; let sig_tvs' = map (tcGetTyVar "mkExport") sig_tys
+ ; return (sig_tvs', poly_id, mono_id, prags) }
+ -- We zonk the sig_tvs here so that the export triple
+ -- always has zonked type variables;
+ -- a convenient invariant
+
+
+------------------------
+type TcPragFun = Name -> [LSig Name]
+
+mkPragFun :: [LSig Name] -> TcPragFun
+mkPragFun sigs = \n -> lookupNameEnv env n `orElse` []
+ where
+ prs = [(expectJust "mkPragFun" (sigName sig), sig)
+ | sig <- sigs, isPragLSig sig]
+ env = foldl add emptyNameEnv prs
+ add env (n,p) = extendNameEnv_Acc (:) singleton env n p
+
+tcPrags :: Id -> [LSig Name] -> TcM [Prag]
+tcPrags poly_id prags = mapM tc_prag prags
+ where
+ tc_prag (L loc prag) = setSrcSpan loc $
+ addErrCtxt (pragSigCtxt prag) $
+ tcPrag poly_id prag
+
+pragSigCtxt prag = hang (ptext SLIT("In the pragma")) 2 (ppr prag)
+
+tcPrag :: TcId -> Sig Name -> TcM Prag
+tcPrag poly_id (SpecSig orig_name hs_ty inl) = tcSpecPrag poly_id hs_ty inl
+tcPrag poly_id (SpecInstSig hs_ty) = tcSpecPrag poly_id hs_ty defaultInlineSpec
+tcPrag poly_id (InlineSig v inl) = return (InlinePrag inl)
+
+
+tcSpecPrag :: TcId -> LHsType Name -> InlineSpec -> TcM Prag
+tcSpecPrag poly_id hs_ty inl
+ = do { spec_ty <- tcHsSigType (FunSigCtxt (idName poly_id)) hs_ty
+ ; (co_fn, lie) <- getLIE (tcSubExp (idType poly_id) spec_ty)
+ ; extendLIEs lie
+ ; let const_dicts = map instToId lie
+ ; return (SpecPrag (mkHsCoerce co_fn (HsVar poly_id)) spec_ty const_dicts inl) }
+
+--------------
+-- If typechecking the binds fails, then return with each
+-- signature-less binder given type (forall a.a), to minimise
+-- subsequent error messages
+recoveryCode binder_names
+ = do { traceTc (text "tcBindsWithSigs: error recovery" <+> ppr binder_names)
+ ; poly_ids <- mapM mk_dummy binder_names
+ ; return ([], poly_ids) }
where
- -- new_after :: E -> TcM (thing, LIE, thing_ty)
- -- Can't write this signature, cos it's monomorphic in thing and
- -- thing_ty.
- new_after e = tcBindsAndThen top_level e combiner binds2 do_next
+ mk_dummy name = do { mb_id <- tcLookupLocalId_maybe name
+ ; case mb_id of
+ Just id -> return id -- Had signature, was in envt
+ Nothing -> return (mkLocalId name forall_a_a) } -- No signature
+
+forall_a_a :: TcType
+forall_a_a = mkForAllTy alphaTyVar (mkTyVarTy alphaTyVar)
+
+
+-- Check that non-overloaded unlifted bindings are
+-- a) non-recursive,
+-- b) not top level,
+-- c) not a multiple-binding group (more or less implied by (a))
+
+checkStrictBinds :: TopLevelFlag -> RecFlag
+ -> LHsBinds TcId -> [TcType] -> [MonoBindInfo]
+ -> TcM Bool
+checkStrictBinds top_lvl rec_group mbind mono_tys infos
+ | unlifted || bang_pat
+ = do { checkTc (isNotTopLevel top_lvl)
+ (strictBindErr "Top-level" unlifted mbind)
+ ; checkTc (isNonRec rec_group)
+ (strictBindErr "Recursive" unlifted mbind)
+ ; checkTc (isSingletonBag mbind)
+ (strictBindErr "Multiple" unlifted mbind)
+ ; mapM_ check_sig infos
+ ; return True }
+ | otherwise
+ = return False
+ where
+ unlifted = any isUnLiftedType mono_tys
+ bang_pat = anyBag (isBangHsBind . unLoc) mbind
+ check_sig (_, Just sig, _) = checkTc (null (sig_tvs sig) && null (sig_theta sig))
+ (badStrictSig unlifted sig)
+ check_sig other = return ()
+
+strictBindErr flavour unlifted mbind
+ = hang (text flavour <+> msg <+> ptext SLIT("aren't allowed:")) 4 (ppr mbind)
+ where
+ msg | unlifted = ptext SLIT("bindings for unlifted types")
+ | otherwise = ptext SLIT("bang-pattern bindings")
+
+badStrictSig unlifted sig
+ = hang (ptext SLIT("Illegal polymorphic signature in") <+> msg)
+ 4 (ppr sig)
+ where
+ msg | unlifted = ptext SLIT("an unlifted binding")
+ | otherwise = ptext SLIT("a bang-pattern binding")
\end{code}
-Simple wrappers for export:
+
+%************************************************************************
+%* *
+\subsection{tcMonoBind}
+%* *
+%************************************************************************
+
+@tcMonoBinds@ deals with a perhaps-recursive group of HsBinds.
+The signatures have been dealt with already.
+
\begin{code}
-tcTopBindsAndThen
- :: E
- -> (TypecheckedBinds -> thing -> thing) -- Combinator
- -> RenamedBinds
- -> (E -> TcM (thing, LIE, anything))
- -> TcM (thing, LIE, anything)
-
-tcTopBindsAndThen e combiner binds do_next
- = tcBindsAndThen True e combiner binds do_next
-
-tcLocalBindsAndThen
- :: E
- -> (TypecheckedBinds -> thing -> thing) -- Combinator
- -> RenamedBinds
- -> (E -> TcM (thing, LIE, thing_ty))
- -> TcM (thing, LIE, thing_ty)
-
-tcLocalBindsAndThen e combiner binds do_next
- = tcBindsAndThen False e combiner binds do_next
-\end{code}
+tcMonoBinds :: [LHsBind Name]
+ -> TcSigFun
+ -> RecFlag -- Whether the binding is recursive for typechecking purposes
+ -- i.e. the binders are mentioned in their RHSs, and
+ -- we are not resuced by a type signature
+ -> TcM (LHsBinds TcId, [MonoBindInfo])
+
+tcMonoBinds [L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf,
+ fun_matches = matches, bind_fvs = fvs })]
+ sig_fn -- Single function binding,
+ NonRecursive -- binder isn't mentioned in RHS,
+ | Nothing <- sig_fn name -- ...with no type signature
+ = -- In this very special case we infer the type of the
+ -- right hand side first (it may have a higher-rank type)
+ -- and *then* make the monomorphic Id for the LHS
+ -- e.g. f = \(x::forall a. a->a) -> <body>
+ -- We want to infer a higher-rank type for f
+ setSrcSpan b_loc $
+ do { ((co_fn, matches'), rhs_ty) <- tcInfer (tcMatchesFun name matches)
+
+ -- Check for an unboxed tuple type
+ -- f = (# True, False #)
+ -- Zonk first just in case it's hidden inside a meta type variable
+ -- (This shows up as a (more obscure) kind error
+ -- in the 'otherwise' case of tcMonoBinds.)
+ ; zonked_rhs_ty <- zonkTcType rhs_ty
+ ; checkTc (not (isUnboxedTupleType zonked_rhs_ty))
+ (unboxedTupleErr name zonked_rhs_ty)
+
+ ; mono_name <- newLocalName name
+ ; let mono_id = mkLocalId mono_name zonked_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 })),
+ [(name, Nothing, mono_id)]) }
+
+tcMonoBinds [L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf,
+ fun_matches = matches, bind_fvs = fvs })]
+ sig_fn -- Single function binding
+ non_rec
+ | Just sig <- sig_fn name -- ...with a type signature
+ = -- When we have a single function binding, with a type signature
+ -- we can (a) use genuine, rigid skolem constants for the type variables
+ -- (b) bring (rigid) scoped type variables into scope
+ setSrcSpan b_loc $
+ do { tc_sig <- tcInstSig True sig
+ ; mono_name <- newLocalName name
+ ; let mono_ty = sig_tau tc_sig
+ mono_id = mkLocalId mono_name mono_ty
+ rhs_tvs = [ (name, mkTyVarTy tv)
+ | (name, tv) <- sig_scoped tc_sig `zip` sig_tvs tc_sig ]
+
+ ; (co_fn, matches') <- tcExtendTyVarEnv2 rhs_tvs $
+ tcMatchesFun mono_name matches mono_ty
+
+ ; let fun_bind' = FunBind { fun_id = L nm_loc mono_id,
+ fun_infix = inf, fun_matches = matches',
+ bind_fvs = placeHolderNames, fun_co_fn = co_fn }
+ ; return (unitBag (L b_loc fun_bind'),
+ [(name, Just tc_sig, mono_id)]) }
+
+tcMonoBinds binds sig_fn non_rec
+ = do { tc_binds <- mapM (wrapLocM (tcLhs sig_fn)) binds
+
+ -- Bring the monomorphic Ids, into scope for the RHSs
+ ; let mono_info = getMonoBindInfo tc_binds
+ rhs_id_env = [(name,mono_id) | (name, Nothing, mono_id) <- mono_info]
+ -- A monomorphic binding for each term variable that lacks
+ -- a type sig. (Ones with a sig are already in scope.)
+
+ ; binds' <- tcExtendIdEnv2 rhs_id_env $
+ traceTc (text "tcMonoBinds" <+> vcat [ ppr n <+> ppr id <+> ppr (idType id)
+ | (n,id) <- rhs_id_env]) `thenM_`
+ mapM (wrapLocM tcRhs) tc_binds
+ ; return (listToBag binds', mono_info) }
+
+------------------------
+-- tcLhs typechecks the LHS of the bindings, to construct the environment in which
+-- we typecheck the RHSs. Basically what we are doing is this: for each binder:
+-- if there's a signature for it, use the instantiated signature type
+-- otherwise invent a type variable
+-- You see that quite directly in the FunBind case.
+--
+-- But there's a complication for pattern bindings:
+-- data T = MkT (forall a. a->a)
+-- MkT f = e
+-- Here we can guess a type variable for the entire LHS (which will be refined to T)
+-- but we want to get (f::forall a. a->a) as the RHS environment.
+-- The simplest way to do this is to typecheck the pattern, and then look up the
+-- bound mono-ids. Then we want to retain the typechecked pattern to avoid re-doing
+-- it; hence the TcMonoBind data type in which the LHS is done but the RHS isn't
+
+data TcMonoBind -- Half completed; LHS done, RHS not done
+ = TcFunBind MonoBindInfo (Located TcId) Bool (MatchGroup Name)
+ | TcPatBind [MonoBindInfo] (LPat TcId) (GRHSs Name) TcSigmaType
+
+type MonoBindInfo = (Name, Maybe TcSigInfo, TcId)
+ -- Type signature (if any), and
+ -- the monomorphic bound things
+
+bndrNames :: [MonoBindInfo] -> [Name]
+bndrNames mbi = [n | (n,_,_) <- mbi]
+
+getMonoType :: MonoBindInfo -> TcTauType
+getMonoType (_,_,mono_id) = idType mono_id
+
+tcLhs :: TcSigFun -> HsBind Name -> TcM TcMonoBind
+tcLhs sig_fn (FunBind { fun_id = L nm_loc name, fun_infix = inf, fun_matches = matches })
+ = do { mb_sig <- tcInstSig_maybe (sig_fn name)
+ ; mono_name <- newLocalName name
+ ; mono_ty <- mk_mono_ty mb_sig
+ ; let mono_id = mkLocalId mono_name mono_ty
+ ; return (TcFunBind (name, mb_sig, mono_id) (L nm_loc mono_id) inf matches) }
+ where
+ mk_mono_ty (Just sig) = return (sig_tau sig)
+ mk_mono_ty Nothing = newFlexiTyVarTy argTypeKind
+
+tcLhs sig_fn bind@(PatBind { pat_lhs = pat, pat_rhs = grhss })
+ = do { mb_sigs <- mapM (tcInstSig_maybe . sig_fn) names
-An aside. The original version of @tcBindsAndThen@ which lacks a
-combiner function, appears below. Though it is perfectly well
-behaved, it cannot be typed by Haskell, because the recursive call is
-at a different type to the definition itself. There aren't too many
-examples of this, which is why I thought it worth preserving! [SLPJ]
+ ; let nm_sig_prs = names `zip` mb_sigs
+ tau_sig_env = mkNameEnv [ (name, sig_tau sig) | (name, Just sig) <- nm_sig_prs]
+ sig_tau_fn = lookupNameEnv tau_sig_env
-\begin{pseudocode}
-tcBindsAndThen
- :: Bool -> E -> RenamedBinds
- -> (E -> TcM (thing, LIE, thing_ty))
- -> TcM ((TypecheckedBinds, thing), LIE, thing_ty)
+ tc_pat exp_ty = tcPat (LetPat sig_tau_fn) pat exp_ty unitTy $ \ _ ->
+ mapM lookup_info nm_sig_prs
+ -- The unitTy is a bit bogus; it's the "result type" for lookup_info.
-tcBindsAndThen top_level e EmptyBinds do_next
- = do_next e `thenTc` \ (thing, lie, thing_ty) ->
- returnTc ((EmptyBinds, thing), lie, thing_ty)
+ -- After typechecking the pattern, look up the binder
+ -- names, which the pattern has brought into scope.
+ lookup_info :: (Name, Maybe TcSigInfo) -> TcM MonoBindInfo
+ lookup_info (name, mb_sig) = do { mono_id <- tcLookupId name
+ ; return (name, mb_sig, mono_id) }
-tcBindsAndThen top_level e (SingleBind bind) do_next
- = tcBindAndThen top_level e bind [] do_next
+ ; ((pat', infos), pat_ty) <- addErrCtxt (patMonoBindsCtxt pat grhss) $
+ tcInfer tc_pat
+
+ ; return (TcPatBind infos pat' grhss pat_ty) }
+ where
+ names = collectPatBinders pat
-tcBindsAndThen top_level e (BindWith bind sigs) do_next
- = tcBindAndThen top_level e bind sigs do_next
-tcBindsAndThen top_level e (ThenBinds binds1 binds2) do_next
- = tcBindsAndThen top_level e binds1 new_after
- `thenTc` \ ((binds1', (binds2', thing')), lie1, thing_ty) ->
+tcLhs sig_fn other_bind = pprPanic "tcLhs" (ppr other_bind)
+ -- AbsBind, VarBind impossible
- returnTc ((binds1' `ThenBinds` binds2', thing'), lie1, thing_ty)
+-------------------
+tcRhs :: TcMonoBind -> TcM (HsBind TcId)
+tcRhs (TcFunBind info fun'@(L _ mono_id) inf matches)
+ = do { (co_fn, matches') <- tcMatchesFun (idName mono_id) matches
+ (idType mono_id)
+ ; return (FunBind { fun_id = fun', fun_infix = inf, fun_matches = matches',
+ bind_fvs = placeHolderNames, fun_co_fn = co_fn }) }
+tcRhs bind@(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
- -- new_after :: E -> TcM ((TypecheckedBinds, thing), LIE, thing_ty)
- -- Can't write this signature, cos it's monomorphic in thing and thing_ty
- new_after e = tcBindsAndThen top_level e binds2 do_next
-\end{pseudocode}
+ get_info (TcFunBind info _ _ _) rest = info : rest
+ get_info (TcPatBind infos _ _ _) rest = infos ++ rest
+\end{code}
+
%************************************************************************
%* *
-\subsection{Bind}
+ Generalisation
%* *
%************************************************************************
\begin{code}
-tcBindAndThen
- :: Bool -- At top level
- -> E
- -> (TypecheckedBinds -> thing -> thing) -- Combinator
- -> RenamedBind -- The Bind to typecheck
- -> [RenamedSig] -- ...and its signatures
- -> (E -> TcM (thing, LIE, thing_ty)) -- Thing to type check in
- -- augmented envt
- -> TcM (thing, LIE, thing_ty) -- Results, incl the
-
-tcBindAndThen top_level e combiner bind sigs do_next
- = -- Deal with the bind
- tcBind top_level e bind sigs `thenTc` \ (poly_binds, poly_lie, poly_lve) ->
-
- -- Now do whatever happens next, in the augmented envt
- do_next (growE_LVE e poly_lve) `thenTc` \ (thing, thing_lie, thing_ty) ->
- let
- bound_ids = map snd poly_lve
- in
- -- Create specialisations
- specialiseBinds bound_ids thing_lie poly_binds poly_lie
- `thenNF_Tc` \ (final_binds, final_lie) ->
- -- All done
- returnTc (combiner final_binds thing, final_lie, thing_ty)
+generalise :: TopLevelFlag -> Bool
+ -> [MonoBindInfo] -> [Inst]
+ -> TcM ([TcTyVar], TcDictBinds, [TcId])
+generalise top_lvl is_unrestricted mono_infos lie_req
+ | not is_unrestricted -- RESTRICTED CASE
+ = -- Check signature contexts are empty
+ do { checkTc (all is_mono_sig sigs)
+ (restrictedBindCtxtErr bndrs)
+
+ -- Now simplify with exactly that set of tyvars
+ -- We have to squash those Methods
+ ; (qtvs, binds) <- tcSimplifyRestricted doc top_lvl bndrs
+ tau_tvs lie_req
+
+ -- Check that signature type variables are OK
+ ; final_qtvs <- checkSigsTyVars qtvs sigs
+
+ ; return (final_qtvs, binds, []) }
+
+ | null sigs -- UNRESTRICTED CASE, NO TYPE SIGS
+ = tcSimplifyInfer doc tau_tvs lie_req
+
+ | otherwise -- UNRESTRICTED CASE, WITH TYPE SIGS
+ = do { sig_lie <- unifyCtxts sigs -- sigs is non-empty
+ ; let -- The "sig_avails" is the stuff available. We get that from
+ -- the context of the type signature, BUT ALSO the lie_avail
+ -- so that polymorphic recursion works right (see Note [Polymorphic recursion])
+ local_meths = [mkMethInst sig mono_id | (_, Just sig, mono_id) <- mono_infos]
+ sig_avails = sig_lie ++ local_meths
+
+ -- Check that the needed dicts can be
+ -- expressed in terms of the signature ones
+ ; (forall_tvs, dict_binds) <- tcSimplifyInferCheck doc tau_tvs sig_avails lie_req
+
+ -- Check that signature type variables are OK
+ ; final_qtvs <- checkSigsTyVars forall_tvs sigs
+
+ ; returnM (final_qtvs, dict_binds, map instToId sig_lie) }
+ where
+ bndrs = bndrNames mono_infos
+ sigs = [sig | (_, Just sig, _) <- mono_infos]
+ tau_tvs = foldr (unionVarSet . exactTyVarsOfType . getMonoType) emptyVarSet mono_infos
+ -- NB: exactTyVarsOfType; see Note [Silly type synonym]
+ -- near defn of TcType.exactTyVarsOfType
+ is_mono_sig sig = null (sig_theta sig)
+ doc = ptext SLIT("type signature(s) for") <+> pprBinders bndrs
+
+ mkMethInst (TcSigInfo { sig_id = poly_id, sig_tvs = tvs,
+ sig_theta = theta, sig_loc = loc }) mono_id
+ = Method mono_id poly_id (mkTyVarTys tvs) theta loc
\end{code}
+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}
-tcBind :: Bool -> E
- -> RenamedBind -> [RenamedSig]
- -> TcM (TypecheckedBinds, LIE, LVE) -- LIE is a fixed point of substitution
+unifyCtxts :: [TcSigInfo] -> TcM [Inst]
+unifyCtxts (sig1 : sigs) -- Argument is always non-empty
+ = do { mapM unify_ctxt sigs
+ ; newDictsAtLoc (sig_loc sig1) (sig_theta sig1) }
+ where
+ theta1 = sig_theta sig1
+ unify_ctxt :: TcSigInfo -> TcM ()
+ unify_ctxt sig@(TcSigInfo { sig_theta = theta })
+ = setSrcSpan (instLocSrcSpan (sig_loc sig)) $
+ addErrCtxt (sigContextsCtxt sig1 sig) $
+ unifyTheta theta1 theta
+
+checkSigsTyVars :: [TcTyVar] -> [TcSigInfo] -> TcM [TcTyVar]
+checkSigsTyVars qtvs sigs
+ = do { gbl_tvs <- tcGetGlobalTyVars
+ ; sig_tvs_s <- mappM (check_sig gbl_tvs) sigs
+
+ ; let -- Sigh. Make sure that all the tyvars in the type sigs
+ -- appear in the returned ty var list, which is what we are
+ -- going to generalise over. Reason: we occasionally get
+ -- silly types like
+ -- type T a = () -> ()
+ -- f :: T a
+ -- f () = ()
+ -- Here, 'a' won't appear in qtvs, so we have to add it
+ sig_tvs = foldl extendVarSetList emptyVarSet sig_tvs_s
+ all_tvs = varSetElems (extendVarSetList sig_tvs qtvs)
+ ; returnM all_tvs }
+ where
+ check_sig gbl_tvs (TcSigInfo {sig_id = id, sig_tvs = tvs,
+ sig_theta = theta, sig_tau = tau})
+ = addErrCtxt (ptext SLIT("In the type signature for") <+> quotes (ppr id)) $
+ addErrCtxtM (sigCtxt id tvs theta tau) $
+ do { tvs' <- checkDistinctTyVars tvs
+ ; ifM (any (`elemVarSet` gbl_tvs) tvs')
+ (bleatEscapedTvs gbl_tvs tvs tvs')
+ ; return tvs' }
+
+checkDistinctTyVars :: [TcTyVar] -> TcM [TcTyVar]
+-- (checkDistinctTyVars tvs) checks that the tvs from one type signature
+-- are still all type variables, and all distinct from each other.
+-- It returns a zonked set of type variables.
+-- For example, if the type sig is
+-- f :: forall a b. a -> b -> b
+-- we want to check that 'a' and 'b' haven't
+-- (a) been unified with a non-tyvar type
+-- (b) been unified with each other (all distinct)
+
+checkDistinctTyVars sig_tvs
+ = do { zonked_tvs <- mapM zonkSigTyVar sig_tvs
+ ; foldlM check_dup emptyVarEnv (sig_tvs `zip` zonked_tvs)
+ ; return zonked_tvs }
+ where
+ check_dup :: TyVarEnv TcTyVar -> (TcTyVar, TcTyVar) -> TcM (TyVarEnv TcTyVar)
+ -- The TyVarEnv maps each zonked type variable back to its
+ -- corresponding user-written signature type variable
+ check_dup acc (sig_tv, zonked_tv)
+ = case lookupVarEnv acc zonked_tv of
+ Just sig_tv' -> bomb_out sig_tv sig_tv'
+
+ Nothing -> return (extendVarEnv acc zonked_tv sig_tv)
+
+ bomb_out sig_tv1 sig_tv2
+ = do { env0 <- tcInitTidyEnv
+ ; let (env1, tidy_tv1) = tidyOpenTyVar env0 sig_tv1
+ (env2, tidy_tv2) = tidyOpenTyVar env1 sig_tv2
+ msg = ptext SLIT("Quantified type variable") <+> quotes (ppr tidy_tv1)
+ <+> ptext SLIT("is unified with another quantified type variable")
+ <+> quotes (ppr tidy_tv2)
+ ; failWithTcM (env2, msg) }
+ where
+\end{code}
+
-tcBind False e bind sigs -- Not top level
- = tcBind_help False e bind sigs
+@getTyVarsToGen@ decides what type variables to generalise over.
-tcBind True e bind sigs -- Top level!
- = pruneSubstTc (tvOfE e) (
+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
- -- DO THE WORK
- tcBind_help True e bind sigs `thenTc` \ (new_binds, lie, lve) ->
+*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!
-{- Top-level unboxed values are now allowed
- They will be lifted by the Desugarer (see CoreLift.lhs)
+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:
- -- CHECK FOR PRIMITIVE TOP-LEVEL BINDS
- listTc [ checkTc (isUnboxedDataType (getIdUniType id))
- (topLevelUnboxedDeclErr id (getSrcLoc id))
- | (_,id) <- lve ] `thenTc_`
--}
+ (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]
- -- Back-substitute over the binds, since we are about to discard
- -- a good chunk of the substitution.
- applyTcSubstToBinds new_binds `thenNF_Tc` \ final_binds ->
+ (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.
- -- The lie is already a fixed point of the substitution; it just turns out
- -- that almost always this happens automatically, and so we made it part of
- -- the specification of genBinds.
- returnTc (final_binds, lie, lve)
- )
-\end{code}
+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.
-\begin{code}
-tcBind_help top_level e bind sigs
- = -- Create an LVE binding each identifier to an appropriate type variable
- new_locals binders `thenNF_Tc` \ bound_ids ->
- let lve = binders `zip` bound_ids in
-
- -- Now deal with type signatures, if any
- tcSigs e lve sigs `thenTc` \ sig_info ->
-
- -- Check the bindings: this is the point at which we can use
- -- error recovery. If checking the bind fails we just
- -- return the empty bindings. The variables will still be in
- -- scope, but bound to completely free type variables, which
- -- is just what we want to minimise subsequent error messages.
- recoverTc (NonRecBind EmptyMonoBinds, nullLIE)
- (tc_bind (growE_LVE e lve) bind) `thenNF_Tc` \ (bind', lie) ->
-
- -- Notice that genBinds gets the old (non-extended) environment
- genBinds top_level e bind' lie lve sig_info `thenTc` \ (binds', lie, lve) ->
-
- -- Add bindings corresponding to SPECIALIZE pragmas in the code
- mapAndUnzipTc (doSpecPragma e (assoc "doSpecPragma" lve))
- (get_spec_pragmas sig_info)
- `thenTc` \ (spec_binds_s, spec_lie_s) ->
-
- returnTc (binds' `ThenBinds` (SingleBind (NonRecBind (
- foldr AndMonoBinds EmptyMonoBinds spec_binds_s))),
- lie `plusLIE` (foldr plusLIE nullLIE spec_lie_s),
- lve)
- where
- binders = collectBinders bind
+Note [Polymorphic recursion]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The game plan for polymorphic recursion in the code above is
- new_locals binders
- = case bind of
- NonRecBind _ -> -- Recursive, so no unboxed types
- newLocalsWithOpenTyVarTys binders
+ * 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.
- RecBind _ -> -- Non-recursive, so we permit unboxed types
- newLocalsWithPolyTyVarTys binders
+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:
- get_spec_pragmas sig_info
- = catMaybes (map get_pragma_maybe sig_info)
- where
- get_pragma_maybe s@(ValSpecInfo _ _ _ _) = Just s
- get_pragma_maybe _ = Nothing
-\end{code}
+ f :: Eq a => [a] -> [a]
+ f xs = ...f...
-\begin{verbatim}
- f :: Ord a => [a] -> b -> b
- {-# SPECIALIZE f :: [Int] -> b -> b #-}
-\end{verbatim}
-We generate:
-\begin{verbatim}
- f@Int = /\ b -> let d1 = ...
- in f Int b d1
+If we don't take care, after typechecking we get
+ f = /\a -> \d::Eq a -> let f' = f a d
+ in
+ \ys:[a] -> ...f'...
- h :: Ord a => [a] -> b -> b
- {-# SPECIALIZE h :: [Int] -> b -> b #-}
+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)
- spec_h = /\b -> h [Int] b dListOfInt
- ^^^^^^^^^^^^^^^^^^^^ This bit created by specId
-\end{verbatim}
+ ff :: [Int] -> [Int]
+ ff = f Int dEqInt
-\begin{code}
-doSpecPragma :: E
- -> (Name -> Id)
- -> SignatureInfo
- -> TcM (TypecheckedMonoBinds, LIE)
-
-doSpecPragma e name_to_id (ValSpecInfo name spec_ty using src_loc)
- = let
- main_id = name_to_id name -- Get the parent Id
-
- main_id_ty = getIdUniType main_id
- main_id_free_tyvars = extractTyVarsFromTy main_id_ty
- origin = ValSpecOrigin name src_loc
- err_ctxt = ValSpecSigCtxt name spec_ty src_loc
- in
- addSrcLocTc src_loc (
- specTy origin spec_ty `thenNF_Tc` \ (spec_tyvars, spec_dicts, spec_tau) ->
-
- -- Check that the SPECIALIZE pragma had an empty context
- checkTc (not (null spec_dicts))
- (panic "SPECIALIZE non-empty context (ToDo: msg)") `thenTc_`
-
- -- Make an instance of this id
- specTy origin main_id_ty `thenNF_Tc` \ (main_tyvars, main_dicts, main_tau) ->
-
- -- Check that the specialised type is indeed an instance of
- -- the inferred type.
- -- The unification should leave all type vars which are
- -- currently free in the environment still free, and likewise
- -- the signature type vars.
- -- The only way type vars free in the envt could possibly be affected
- -- is if main_id_ty has free type variables. So we just extract them,
- -- and check that they are not constrained in any way by the unification.
- applyTcSubstAndCollectTyVars main_id_free_tyvars `thenNF_Tc` \ free_tyvars' ->
- unifyTauTy spec_tau main_tau err_ctxt `thenTc_`
- checkSigTyVars [] (spec_tyvars ++ free_tyvars')
- spec_tau main_tau err_ctxt `thenTc_`
-
- -- Check that the type variables of the polymorphic function are
- -- either left polymorphic, or instantiate to ground type.
- -- Also check that the overloaded type variables are instantiated to
- -- ground type; or equivalently that all dictionaries have ground type
- applyTcSubstToTyVars main_tyvars `thenNF_Tc` \ main_arg_tys ->
- applyTcSubstToInsts main_dicts `thenNF_Tc` \ main_dicts' ->
-
- checkTc (not (all isGroundOrTyVarTy main_arg_tys))
- (specGroundnessErr err_ctxt main_arg_tys)
- `thenTc_`
-
- checkTc (not (and [isGroundTy ty | (_,ty) <- map getDictClassAndType main_dicts']))
- (specCtxtGroundnessErr err_ctxt main_dicts')
- `thenTc_`
-
- -- Build a suitable binding; depending on whether we were given
- -- a value (Maybe Name) to be used as the specialisation.
- case using of
- Nothing ->
-
- -- Make a specPragmaId to which to bind the new call-instance
- newSpecPragmaId name spec_ty Nothing
- `thenNF_Tc` \ pseudo_spec_id ->
- let
- pseudo_bind = VarMonoBind pseudo_spec_id pseudo_rhs
- pseudo_rhs = mkTyLam spec_tyvars (mkDictApp (mkTyApp (Var main_id) main_arg_tys)
- (map mkInstId main_dicts'))
- in
- returnTc (pseudo_bind, mkLIE main_dicts')
-
- Just spec_name -> -- use spec_name as the specialisation value ...
- let
- spec_id = lookupE_Value e spec_name
- spec_id_ty = getIdUniType spec_id
-
- spec_id_free_tyvars = extractTyVarsFromTy spec_id_ty
- spec_id_ctxt = ValSpecSpecIdCtxt name spec_ty spec_name src_loc
-
- spec_tys = map maybe_ty main_arg_tys
- maybe_ty ty | isTyVarTy ty = Nothing
- | otherwise = Just ty
- in
- -- Make an instance of the spec_id
- specTy origin spec_id_ty `thenNF_Tc` \ (spec_id_tyvars, spec_id_dicts, spec_id_tau) ->
-
- -- Check that the specialised type is indeed an instance of
- -- the type inferred for spec_id
- -- The unification should leave all type vars which are
- -- currently free in the environment still free, and likewise
- -- the signature type vars.
- -- The only way type vars free in the envt could possibly be affected
- -- is if spec_id_ty has free type variables. So we just extract them,
- -- and check that they are not constrained in any way by the unification.
- applyTcSubstAndCollectTyVars spec_id_free_tyvars `thenNF_Tc` \ spec_id_free_tyvars' ->
- unifyTauTy spec_tau spec_id_tau spec_id_ctxt `thenTc_`
- checkSigTyVars [] (spec_tyvars ++ spec_id_free_tyvars')
- spec_tau spec_id_tau spec_id_ctxt `thenTc_`
-
- -- Check that the type variables of the explicit spec_id are
- -- either left polymorphic, or instantiate to ground type.
- -- Also check that the overloaded type variables are instantiated to
- -- ground type; or equivalently that all dictionaries have ground type
- applyTcSubstToTyVars spec_id_tyvars `thenNF_Tc` \ spec_id_arg_tys ->
- applyTcSubstToInsts spec_id_dicts `thenNF_Tc` \ spec_id_dicts' ->
-
- checkTc (not (all isGroundOrTyVarTy spec_id_arg_tys))
- (specGroundnessErr spec_id_ctxt spec_id_arg_tys)
- `thenTc_`
-
- checkTc (not (and [isGroundTy ty | (_,ty) <- map getDictClassAndType spec_id_dicts']))
- (specCtxtGroundnessErr spec_id_ctxt spec_id_dicts')
- `thenTc_`
-
- -- Make a local SpecId to bind to applied spec_id
- newSpecId main_id spec_tys spec_ty `thenNF_Tc` \ local_spec_id ->
-
- -- Make a specPragmaId id with a spec_info for local_spec_id
- -- This is bound to local_spec_id
- -- The SpecInfo will be extracted by the specialiser and
- -- used to create a call instance for main_id (which is
- -- extracted from the spec_id)
- -- NB: the pseudo_local_id must stay in the scope of main_id !!!
- let
- spec_info = SpecInfo spec_tys (length main_dicts') local_spec_id
- in
- newSpecPragmaId name spec_ty (Just spec_info) `thenNF_Tc` \ pseudo_spec_id ->
- let
- spec_bind = VarMonoBind local_spec_id spec_rhs
- spec_rhs = mkTyLam spec_tyvars (mkDictApp (mkTyApp (Var spec_id) spec_id_arg_tys)
- (map mkInstId spec_id_dicts'))
- pseudo_bind = VarMonoBind pseudo_spec_id (Var local_spec_id)
- in
- returnTc (spec_bind `AndMonoBinds` pseudo_bind, mkLIE spec_id_dicts')
- )
-\end{code}
+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.
-\begin{code}
-tc_bind :: E
- -> RenamedBind
- -> TcM (TypecheckedBind, LIE)
+ ff = f Int dEqInt
-tc_bind e (NonRecBind mono_binds)
- = tcMonoBinds e mono_binds `thenTc` \ (mono_binds2, lie) ->
- returnTc (NonRecBind mono_binds2, lie)
+ = 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
-tc_bind e (RecBind mono_binds)
- = tcMonoBinds e mono_binds `thenTc` \ (mono_binds2, lie) ->
- returnTc (RecBind mono_binds2, lie)
-\end{code}
-\begin{code}
-specialiseBinds
- :: [Id] -- Ids bound in this group
- -> LIE -- LIE of scope of these bindings
- -> TypecheckedBinds
- -> LIE
- -> NF_TcM (TypecheckedBinds, LIE)
-
-specialiseBinds bound_ids lie_of_scope poly_binds poly_lie
- = bindInstsOfLocalFuns lie_of_scope bound_ids
- `thenNF_Tc` \ (lie2, inst_mbinds) ->
-
- returnNF_Tc (poly_binds `ThenBinds` (SingleBind (NonRecBind inst_mbinds)),
- lie2 `plusLIE` poly_lie)
-\end{code}
%************************************************************************
%* *
-\subsection{Signatures}
+ 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 (not @TyVarTemplate@s)
-installed.
+split up, and have fresh type variables installed. All non-type-signature
+"RenamedSigs" are ignored.
-\begin{code}
-tcSigs :: E -> LVE
- -> [RenamedSig]
- -> TcM [SignatureInfo]
+The @TcSigInfo@ contains @TcTypes@ because they are unified with
+the variable's type, and after that checked to see whether they've
+been instantiated.
-tcSigs e lve [] = returnTc []
+\begin{code}
+type TcSigFun = Name -> Maybe (LSig Name)
-tcSigs e lve (s:ss)
- = tc_sig s `thenTc` \ sig_info1 ->
- tcSigs e lve ss `thenTc` \ sig_info2 ->
- returnTc (sig_info1 : sig_info2)
+mkSigFun :: [LSig Name] -> TcSigFun
+-- Search for a particular type signature
+-- Precondition: the sigs are all type sigs
+-- Precondition: no duplicates
+mkSigFun sigs = lookupNameEnv env
where
- tc_sig (Sig v ty _ src_loc) -- no interesting pragmas on non-iface sigs
- = addSrcLocTc src_loc (
-
- babyTcMtoTcM
- (tcPolyType (getE_CE e) (getE_TCE e) nullTVE ty) `thenTc` \ sigma_ty ->
+ env = mkNameEnv [(expectJust "mkSigFun" (sigName sig), sig) | sig <- sigs]
+
+---------------
+data TcSigInfo
+ = TcSigInfo {
+ sig_id :: TcId, -- *Polymorphic* binder for this value...
+
+ sig_scoped :: [Name], -- Names for any scoped type variables
+ -- Invariant: correspond 1-1 with an initial
+ -- segment of sig_tvs (see Note [Scoped])
+
+ sig_tvs :: [TcTyVar], -- Instantiated type variables
+ -- See Note [Instantiate sig]
+
+ sig_theta :: TcThetaType, -- Instantiated theta
+ sig_tau :: TcTauType, -- Instantiated tau
+ sig_loc :: InstLoc -- The location of the signature
+ }
+
+-- Note [Scoped]
+-- There may be more instantiated type variables than 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 sig_scoped
+
+-- Note [Instantiate sig]
+-- It's vital to instantiate a type signature with fresh variable.
+-- For example:
+-- type S = forall a. a->a
+-- f,g :: S
+-- f = ...
+-- g = ...
+-- Here, we must use distinct type variables when checking f,g's right hand sides.
+-- (Instantiation is only necessary because of type synonyms. Otherwise,
+-- it's all cool; each signature has distinct type variables from the renamer.)
+
+instance Outputable TcSigInfo where
+ ppr (TcSigInfo { sig_id = id, sig_tvs = tyvars, sig_theta = theta, sig_tau = tau})
+ = ppr id <+> ptext SLIT("::") <+> ppr tyvars <+> ppr theta <+> ptext SLIT("=>") <+> ppr tau
+\end{code}
- let val = assoc "tcSigs" lve v in
- -- (The renamer/dependency-analyser should have ensured
- -- that there are only signatures for which there is a
- -- corresponding binding.)
+\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) }
+
+-------------------
+tcInstSig_maybe :: Maybe (LSig Name) -> TcM (Maybe TcSigInfo)
+-- Instantiate with *meta* type variables;
+-- this signature is part of a multi-signature group
+tcInstSig_maybe Nothing = return Nothing
+tcInstSig_maybe (Just sig) = do { tc_sig <- tcInstSig False sig
+ ; return (Just tc_sig) }
+
+tcInstSig :: Bool -> LSig Name -> TcM TcSigInfo
+-- Instantiate the signature, with either skolems or meta-type variables
+-- depending on the use_skols boolean
+--
+-- We always instantiate with freshs uniques,
+-- although we keep the same print-name
+--
+-- type T = forall a. [a] -> [a]
+-- f :: T;
+-- f = g where { g :: T; g = <rhs> }
+--
+-- We must not use the same 'a' from the defn of T at both places!!
+
+tcInstSig use_skols (L loc (TypeSig (L _ name) hs_ty))
+ = setSrcSpan loc $
+ do { poly_id <- tcLookupId name -- Cannot fail; the poly ids are put into
+ -- scope when starting the binding group
+ ; let skol_info = SigSkol (FunSigCtxt name)
+ inst_tyvars | use_skols = tcInstSkolTyVars skol_info
+ | otherwise = tcInstSigTyVars skol_info
+ ; (tvs, theta, tau) <- tcInstType inst_tyvars (idType poly_id)
+ ; loc <- getInstLoc (SigOrigin skol_info)
+ ; return (TcSigInfo { sig_id = poly_id,
+ sig_tvs = tvs, sig_theta = theta, sig_tau = tau,
+ sig_scoped = scoped_names, sig_loc = loc }) }
+ -- Note that the scoped_names and the sig_tvs will have
+ -- different Names. That's quite ok; when we bring the
+ -- scoped_names into scope, we just bind them to the sig_tvs
+ where
+ -- The scoped names are the ones explicitly mentioned
+ -- in the HsForAll. (There may be more in sigma_ty, because
+ -- of nested type synonyms. See Note [Scoped] with TcSigInfo.)
+ -- We also only have scoped type variables when we are instantiating
+ -- with true skolems
+ scoped_names = case (use_skols, hs_ty) of
+ (True, L _ (HsForAllTy Explicit tvs _ _)) -> hsLTyVarNames tvs
+ other -> []
+
+-------------------
+isUnRestrictedGroup :: [LHsBind Name] -> TcSigFun -> TcM Bool
+isUnRestrictedGroup binds sig_fn
+ = do { mono_restriction <- doptM Opt_MonomorphismRestriction
+ ; return (not mono_restriction || all_unrestricted) }
+ where
+ all_unrestricted = all (unrestricted . unLoc) binds
+ has_sig n = isJust (sig_fn n)
+
+ unrestricted (PatBind {}) = False
+ unrestricted (VarBind { var_id = v }) = has_sig v
+ unrestricted (FunBind { fun_id = v, fun_matches = matches }) = unrestricted_match matches
+ || has_sig (unLoc v)
+
+ unrestricted_match (MatchGroup (L _ (Match [] _ _) : _) _) = False
+ -- No args => like a pattern binding
+ unrestricted_match other = True
+ -- Some args => a function binding
+\end{code}
- -- Instantiate the type, and unify with the type variable
- -- found in the Id.
- specTy SignatureOrigin sigma_ty `thenNF_Tc` \ (tyvars, dicts, tau_ty) ->
- unifyTauTy (getIdUniType val) tau_ty
- (panic "ToDo: unifyTauTy(tcSigs)") `thenTc_`
- returnTc (TySigInfo val tyvars dicts tau_ty src_loc)
- )
+%************************************************************************
+%* *
+\subsection[TcBinds-errors]{Error contexts and messages}
+%* *
+%************************************************************************
- tc_sig (SpecSig v ty using src_loc)
- = addSrcLocTc src_loc (
- babyTcMtoTcM
- (tcPolyType (getE_CE e) (getE_TCE e) nullTVE ty) `thenTc` \ sigma_ty ->
+\begin{code}
+-- This one is called on LHS, when pat and grhss are both Name
+-- and on RHS, when pat is TcId and grhss is still Name
+patMonoBindsCtxt pat grhss
+ = hang (ptext SLIT("In a pattern binding:")) 4 (pprPatBind pat grhss)
+
+-----------------------------------------------
+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
- returnTc (ValSpecInfo v sigma_ty using src_loc)
- )
- tc_sig (InlineSig v guide locn)
- = returnTc (ValInlineInfo v guide locn)
+-----------------------------------------------
+unboxedTupleErr name ty
+ = hang (ptext SLIT("Illegal binding of unboxed tuple"))
+ 4 (ppr name <+> dcolon <+> ppr ty)
- tc_sig (DeforestSig v locn)
- = returnTc (ValDeforestInfo v locn)
+-----------------------------------------------
+restrictedBindCtxtErr binder_names
+ = hang (ptext SLIT("Illegal overloaded type signature(s)"))
+ 4 (vcat [ptext SLIT("in a binding group for") <+> pprBinders binder_names,
+ ptext SLIT("that falls under the monomorphism restriction")])
- tc_sig (MagicUnfoldingSig v str locn)
- = returnTc (ValMagicUnfoldingInfo v str locn)
+genCtxt binder_names
+ = ptext SLIT("When generalising the type(s) for") <+> pprBinders binder_names
\end{code}