\section[TcBinds]{TcBinds}
\begin{code}
-#include "HsVersions.h"
+module TcBinds ( tcBindsAndThen, tcTopBindsAndThen,
+ tcPragmaSigs, checkSigTyVars, tcBindWithSigs,
+ sigCtxt, TcSigInfo(..) ) where
-module TcBinds ( tcBindsAndThen, tcPragmaSigs, checkSigTyVars, tcBindWithSigs, TcSigInfo(..) ) where
+#include "HsVersions.h"
-IMP_Ubiq()
-#if defined(__GLASGOW_HASKELL__) && __GLASGOW_HASKELL__ <= 201
-IMPORT_DELOOPER(TcLoop) ( tcGRHSsAndBinds )
-#else
import {-# SOURCE #-} TcGRHSs ( tcGRHSsAndBinds )
-#endif
-
-import HsSyn ( HsBinds(..), Sig(..), MonoBinds(..),
- Match, HsType, InPat(..), OutPat(..), HsExpr(..),
- SYN_IE(RecFlag), nonRecursive,
- GRHSsAndBinds, ArithSeqInfo, HsLit, Fake, Stmt, DoOrListComp, Fixity,
- collectMonoBinders )
-import RnHsSyn ( SYN_IE(RenamedHsBinds), RenamedSig(..),
- SYN_IE(RenamedMonoBinds)
+
+import HsSyn ( HsBinds(..), MonoBinds(..), Sig(..), InPat(..),
+ collectMonoBinders
)
-import TcHsSyn ( SYN_IE(TcHsBinds), SYN_IE(TcMonoBinds),
- TcIdOcc(..), SYN_IE(TcIdBndr), SYN_IE(TcExpr),
+import RnHsSyn ( RenamedHsBinds, RenamedSig(..),
+ RenamedMonoBinds
+ )
+import TcHsSyn ( TcHsBinds, TcMonoBinds,
+ TcIdOcc(..), TcIdBndr,
tcIdType
)
import TcMonad
-import Inst ( Inst, SYN_IE(LIE), emptyLIE, plusLIE, InstOrigin(..),
- newDicts, tyVarsOfInst, instToId
+import Inst ( Inst, LIE, emptyLIE, plusLIE, plusLIEs, InstOrigin(..),
+ newDicts, tyVarsOfInst, instToId, newMethodWithGivenTy,
+ zonkInst, pprInsts
)
-import TcEnv ( tcExtendLocalValEnv, tcLookupLocalValueOK, newMonoIds,
+import TcEnv ( tcExtendLocalValEnv, tcLookupLocalValueOK, newLocalId,
tcGetGlobalTyVars, tcExtendGlobalTyVars
)
-import SpecEnv ( SpecEnv )
import TcMatches ( tcMatchesFun )
import TcSimplify ( tcSimplify, tcSimplifyAndCheck )
import TcMonoType ( tcHsType )
import TcPat ( tcPat )
import TcSimplify ( bindInstsOfLocalFuns )
-import TcType ( SYN_IE(TcType), SYN_IE(TcThetaType), SYN_IE(TcTauType),
- SYN_IE(TcTyVarSet), SYN_IE(TcTyVar),
- newTyVarTy, zonkTcType, zonkTcTyVar, zonkTcTyVars,
- newTcTyVar, tcInstSigType, newTyVarTys
+import TcType ( TcType, TcThetaType, TcTauType,
+ TcTyVarSet, TcTyVar,
+ newTyVarTy, newTcTyVar, tcInstSigType, tcInstSigTcType,
+ zonkTcType, zonkTcTypes, zonkTcThetaType, zonkTcTyVar
)
import Unify ( unifyTauTy, unifyTauTyLists )
import Kind ( isUnboxedTypeKind, mkTypeKind, isTypeKind, mkBoxedTypeKind )
-import Id ( GenId, idType, mkUserLocal, mkUserId )
+import Id ( GenId, idType, mkUserId )
import IdInfo ( noIdInfo )
-import Maybes ( maybeToBool, assocMaybe, catMaybes )
+import Maybes ( maybeToBool, assocMaybe )
import Name ( getOccName, getSrcLoc, Name )
import PragmaInfo ( PragmaInfo(..) )
-import Pretty
-import Type ( mkTyVarTy, mkTyVarTys, isTyVarTy, tyVarsOfTypes, eqSimpleTheta,
- mkSigmaTy, splitSigmaTy, mkForAllTys, mkFunTys, getTyVar, mkDictTy,
- splitRhoTy, mkForAllTy, splitForAllTy )
-import TyVar ( GenTyVar, SYN_IE(TyVar), tyVarKind, minusTyVarSet, emptyTyVarSet,
+import Type ( mkTyVarTy, mkTyVarTys, isTyVarTy, tyVarsOfTypes,
+ splitSigmaTy, mkForAllTys, mkFunTys, getTyVar, mkDictTy,
+ splitRhoTy, mkForAllTy, splitForAllTys )
+import TyVar ( GenTyVar, TyVar, tyVarKind, mkTyVarSet, minusTyVarSet, emptyTyVarSet,
elementOfTyVarSet, unionTyVarSets, tyVarSetToList )
-import Bag ( bagToList, foldrBag, isEmptyBag )
-import Util ( isIn, zipEqual, zipWithEqual, zipWith3Equal, hasNoDups, assoc,
- assertPanic, panic, pprTrace )
-import PprType ( GenClass, GenType, GenTyVar )
+import Bag ( bagToList, foldrBag, )
+import Util ( isIn, hasNoDups, assoc )
import Unique ( Unique )
+import BasicTypes ( TopLevelFlag(..), RecFlag(..) )
import SrcLoc ( SrcLoc )
-
-import Outputable --( interppSP, interpp'SP )
-
-
+import Outputable
\end{code}
dictionaries, which we resolve at the module level.
\begin{code}
-tcBindsAndThen
- :: (TcHsBinds s -> thing -> thing) -- Combinator
+tcTopBindsAndThen, tcBindsAndThen
+ :: (RecFlag -> TcMonoBinds s -> this -> that) -- Combinator
-> RenamedHsBinds
- -> TcM s (thing, LIE s)
- -> TcM s (thing, LIE s)
-
-tcBindsAndThen combiner EmptyBinds do_next
- = do_next `thenTc` \ (thing, lie) ->
- returnTc (combiner EmptyBinds thing, lie)
-
-tcBindsAndThen combiner (ThenBinds binds1 binds2) do_next
- = tcBindsAndThen combiner binds1 (tcBindsAndThen combiner binds2 do_next)
+ -> TcM s (this, LIE s)
+ -> TcM s (that, LIE s)
-tcBindsAndThen combiner (MonoBind bind sigs is_rec) do_next
- = fixTc (\ ~(prag_info_fn, _) ->
- -- This is the usual prag_info fix; the PragmaInfo field of an Id
- -- is not inspected till ages later in the compiler, so there
- -- should be no black-hole problems here.
-
- -- TYPECHECK THE SIGNATURES
- mapTc (tcTySig prag_info_fn) ty_sigs `thenTc` \ tc_ty_sigs ->
-
- tcBindWithSigs binder_names bind
- tc_ty_sigs is_rec prag_info_fn `thenTc` \ (poly_binds, poly_lie, poly_ids) ->
-
- -- Extend the environment to bind the new polymorphic Ids
- tcExtendLocalValEnv binder_names poly_ids $
+tcTopBindsAndThen = tc_binds_and_then TopLevel
+tcBindsAndThen = tc_binds_and_then NotTopLevel
- -- Build bindings and IdInfos corresponding to user pragmas
- tcPragmaSigs sigs `thenTc` \ (prag_info_fn, prag_binds, prag_lie) ->
+tc_binds_and_then top_lvl combiner binds do_next
+ = tcBinds top_lvl binds `thenTc` \ (mbinds1, binds_lie, env, ids) ->
+ tcSetEnv env $
-- Now do whatever happens next, in the augmented envt
- do_next `thenTc` \ (thing, thing_lie) ->
+ do_next `thenTc` \ (thing, thing_lie) ->
-- Create specialisations of functions bound here
- bindInstsOfLocalFuns (prag_lie `plusLIE` thing_lie)
- poly_ids `thenTc` \ (lie2, inst_mbinds) ->
+ -- Nota Bene: we glom the bindings all together in a single
+ -- recursive group ("recursive" passed to combiner, below)
+ -- so that we can do thsi bindInsts thing once for all the bindings
+ -- and the thing inside. This saves a quadratic-cost algorithm
+ -- when there's a long sequence of bindings.
+ bindInstsOfLocalFuns (binds_lie `plusLIE` thing_lie) ids `thenTc` \ (final_lie, mbinds2) ->
-- All done
let
- final_lie = lie2 `plusLIE` poly_lie
- final_binds = MonoBind poly_binds [] is_rec `ThenBinds`
- MonoBind inst_mbinds [] nonRecursive `ThenBinds`
- prag_binds
+ final_mbinds = mbinds1 `AndMonoBinds` mbinds2
in
- returnTc (prag_info_fn, (combiner final_binds thing, final_lie))
- ) `thenTc` \ (_, result) ->
+ returnTc (combiner Recursive final_mbinds thing, final_lie)
+
+tcBinds :: TopLevelFlag
+ -> RenamedHsBinds
+ -> TcM s (TcMonoBinds s, LIE s, TcEnv s, [TcIdBndr s])
+ -- The envt is the envt with binders in scope
+ -- The binders are those bound by this group of bindings
+
+tcBinds top_lvl EmptyBinds
+ = tcGetEnv `thenNF_Tc` \ env ->
+ returnTc (EmptyMonoBinds, emptyLIE, env, [])
+
+ -- Short-cut for the rather common case of an empty bunch of bindings
+tcBinds top_lvl (MonoBind EmptyMonoBinds sigs is_rec)
+ = tcGetEnv `thenNF_Tc` \ env ->
+ returnTc (EmptyMonoBinds, emptyLIE, env, [])
+
+tcBinds top_lvl (ThenBinds binds1 binds2)
+ = tcBinds top_lvl binds1 `thenTc` \ (mbinds1, lie1, env1, ids1) ->
+ tcSetEnv env1 $
+ tcBinds top_lvl binds2 `thenTc` \ (mbinds2, lie2, env2, ids2) ->
+ returnTc (mbinds1 `AndMonoBinds` mbinds2, lie1 `plusLIE` lie2, env2, ids1++ids2)
+
+tcBinds top_lvl (MonoBind bind sigs is_rec)
+ = fixTc (\ ~(prag_info_fn, _) ->
+ -- This is the usual prag_info fix; the PragmaInfo field of an Id
+ -- is not inspected till ages later in the compiler, so there
+ -- should be no black-hole problems here.
+
+ -- TYPECHECK THE SIGNATURES
+ mapTc (tcTySig prag_info_fn) ty_sigs `thenTc` \ tc_ty_sigs ->
+
+ tcBindWithSigs top_lvl binder_names bind
+ tc_ty_sigs is_rec prag_info_fn `thenTc` \ (poly_binds, poly_lie, poly_ids) ->
+
+ -- Extend the environment to bind the new polymorphic Ids
+ tcExtendLocalValEnv binder_names poly_ids $
+
+ -- Build bindings and IdInfos corresponding to user pragmas
+ tcPragmaSigs sigs `thenTc` \ (prag_info_fn, prag_binds, prag_lie) ->
+
+ -- Catch the environment and return
+ tcGetEnv `thenNF_Tc` \ env ->
+ returnTc (prag_info_fn, (poly_binds `AndMonoBinds` prag_binds,
+ poly_lie `plusLIE` prag_lie,
+ env, poly_ids)
+ ) ) `thenTc` \ (_, result) ->
returnTc result
where
binder_names = map fst (bagToList (collectMonoBinders bind))
ty_sigs = [sig | sig@(Sig name _ _) <- sigs]
-
\end{code}
An aside. The original version of @tcBindsAndThen@ which lacks a
\begin{code}
tcBindWithSigs
- :: [Name]
+ :: TopLevelFlag
+ -> [Name]
-> RenamedMonoBinds
-> [TcSigInfo s]
-> RecFlag
-> (Name -> PragmaInfo)
-> TcM s (TcMonoBinds s, LIE s, [TcIdBndr s])
-tcBindWithSigs binder_names mbind tc_ty_sigs is_rec prag_info_fn
+tcBindWithSigs top_lvl binder_names mbind tc_ty_sigs is_rec prag_info_fn
= recoverTc (
-- If typechecking the binds fails, then return with each
-- signature-less binder given type (forall a.a), to minimise subsequent
-- Create a new identifier for each binder, with each being given
-- a fresh unique, and a type-variable type.
- tcGetUniques no_of_binders `thenNF_Tc` \ uniqs ->
- mapNF_Tc mk_mono_id_ty binder_names `thenNF_Tc` \ mono_id_tys ->
+ -- For "mono_lies" see comments about polymorphic recursion at the
+ -- end of the function.
+ mapAndUnzipNF_Tc mk_mono_id binder_names `thenNF_Tc` \ (mono_lies, mono_ids) ->
let
- mono_id_tyvars = tyVarsOfTypes mono_id_tys
- mono_ids = zipWith3Equal "tcBindAndSigs" mk_id binder_names uniqs mono_id_tys
- mk_id name uniq ty = mkUserLocal (getOccName name) uniq ty (getSrcLoc name)
+ mono_lie = plusLIEs mono_lies
+ mono_id_tys = map idType mono_ids
in
-- TYPECHECK THE BINDINGS
-- The tyvars_not_to_gen are free in the environment, and hence
-- candidates for generalisation, but sometimes the monomorphism
-- restriction means we can't generalise them nevertheless
- getTyVarsToGen is_unrestricted mono_id_tyvars lie `thenTc` \ (tyvars_not_to_gen, tyvars_to_gen) ->
+ getTyVarsToGen is_unrestricted mono_id_tys lie `thenTc` \ (tyvars_not_to_gen, tyvars_to_gen) ->
-- DEAL WITH TYPE VARIABLE KINDS
- mapTc defaultUncommittedTyVar (tyVarSetToList tyvars_to_gen) `thenTc` \ tyvars_to_gen_list ->
- -- It's important that the final list (tyvars_to_gen_list) is fully
+ -- **** This step can do unification => keep other zonking after this ****
+ mapTc defaultUncommittedTyVar (tyVarSetToList tyvars_to_gen) `thenTc` \ real_tyvars_to_gen_list ->
+ let
+ real_tyvars_to_gen = mkTyVarSet real_tyvars_to_gen_list
+ -- It's important that the final list
+ -- (real_tyvars_to_gen and real_tyvars_to_gen_list) is fully
-- zonked, *including boxity*, because they'll be included in the forall types of
-- the polymorphic Ids, and instances of these Ids will be generated from them.
+ --
+ -- Also NB that tcSimplify takes zonked tyvars as its arg, hence we pass
+ -- real_tyvars_to_gen
--
- -- This step can do unification => keep other zonking after this
+ in
-- SIMPLIFY THE LIE
- tcExtendGlobalTyVars tyvars_not_to_gen (
+ tcExtendGlobalTyVars (tyVarSetToList tyvars_not_to_gen) (
if null tc_ty_sigs then
-- No signatures, so just simplify the lie
- tcSimplify tyvars_to_gen lie `thenTc` \ (lie_free, dict_binds, lie_bound) ->
+ -- NB: no signatures => no polymorphic recursion, so no
+ -- need to use mono_lies (which will be empty anyway)
+ tcSimplify (text "tcBinds1" <+> ppr binder_names)
+ top_lvl real_tyvars_to_gen lie `thenTc` \ (lie_free, dict_binds, lie_bound) ->
returnTc (lie_free, dict_binds, map instToId (bagToList lie_bound))
else
- zonk_theta sig_theta `thenNF_Tc` \ sig_theta' ->
+ zonkTcThetaType sig_theta `thenNF_Tc` \ sig_theta' ->
newDicts SignatureOrigin sig_theta' `thenNF_Tc` \ (dicts_sig, dict_ids) ->
-- It's important that sig_theta is zonked, because
-- dict_id is later used to form the type of the polymorphic thing,
-- and forall-types must be zonked so far as their bound variables
-- are concerned
+ let
+ -- The "givens" is the stuff available. We get that from
+ -- the context of the type signature, BUT ALSO the mono_lie
+ -- so that polymorphic recursion works right (see comments at end of fn)
+ givens = dicts_sig `plusLIE` mono_lie
+ in
+
-- Check that the needed dicts can be expressed in
-- terms of the signature ones
- tcAddErrCtxt (sigsCtxt tysig_names) $
- tcSimplifyAndCheck tyvars_to_gen dicts_sig lie `thenTc` \ (lie_free, dict_binds) ->
+ tcAddErrCtxt (bindSigsCtxt tysig_names) $
+ tcSimplifyAndCheck
+ (ptext SLIT("type signature for") <+>
+ hsep (punctuate comma (map (quotes . ppr) binder_names)))
+ real_tyvars_to_gen givens lie `thenTc` \ (lie_free, dict_binds) ->
+
returnTc (lie_free, dict_binds, dict_ids)
) `thenTc` \ (lie_free, dict_binds, dicts_bound) ->
- ASSERT( not (any (isUnboxedTypeKind . tyVarKind) tyvars_to_gen_list) )
+ ASSERT( not (any (isUnboxedTypeKind . tyVarKind) real_tyvars_to_gen_list) )
-- The instCantBeGeneralised stuff in tcSimplify should have
-- already raised an error if we're trying to generalise an unboxed tyvar
-- (NB: unboxed tyvars are always introduced along with a class constraint)
-- That's why we just use an ASSERT here.
-- BUILD THE POLYMORPHIC RESULT IDs
- mapNF_Tc zonkTcType mono_id_tys `thenNF_Tc` \ zonked_mono_id_types ->
+ zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_types ->
let
exports = zipWith3 mk_export binder_names mono_ids zonked_mono_id_types
dict_tys = map tcIdType dicts_bound
mk_export binder_name mono_id zonked_mono_id_ty
- | maybeToBool maybe_sig = (sig_tyvars, TcId sig_poly_id, TcId mono_id)
- | otherwise = (tyvars_to_gen_list, TcId poly_id, TcId mono_id)
+ | maybeToBool maybe_sig = (sig_tyvars, TcId sig_poly_id, TcId mono_id)
+ | otherwise = (real_tyvars_to_gen_list, TcId poly_id, TcId mono_id)
where
maybe_sig = maybeSig tc_ty_sigs binder_name
Just (TySigInfo _ sig_poly_id sig_tyvars _ _ _) = maybe_sig
poly_id = mkUserId binder_name poly_ty (prag_info_fn binder_name)
- poly_ty = mkForAllTys tyvars_to_gen_list $ mkFunTys dict_tys $ zonked_mono_id_ty
+ poly_ty = mkForAllTys real_tyvars_to_gen_list $ mkFunTys dict_tys $ zonked_mono_id_ty
-- It's important to build a fully-zonked poly_ty, because
-- we'll slurp out its free type variables when extending the
-- local environment (tcExtendLocalValEnv); if it's not zonked
-- BUILD RESULTS
returnTc (
- AbsBinds tyvars_to_gen_list
+ AbsBinds real_tyvars_to_gen_list
dicts_bound
exports
(dict_binds `AndMonoBinds` mbind'),
where
no_of_binders = length binder_names
- mk_mono_id_ty binder_name = case maybeSig tc_ty_sigs binder_name of
- Just (TySigInfo name _ _ _ tau_ty _) -> returnNF_Tc tau_ty -- There's a signature
- otherwise -> newTyVarTy kind -- No signature
+ mk_mono_id binder_name
+ | theres_a_signature -- There's a signature; and it's overloaded,
+ && not (null sig_theta) -- so make a Method
+ = tcAddSrcLoc sig_loc $
+ newMethodWithGivenTy SignatureOrigin
+ (TcId poly_id) (mkTyVarTys sig_tyvars)
+ sig_theta sig_tau `thenNF_Tc` \ (mono_lie, TcId mono_id) ->
+ -- A bit turgid to have to strip the TcId
+ returnNF_Tc (mono_lie, mono_id)
+
+ | otherwise -- No signature or not overloaded;
+ = tcAddSrcLoc (getSrcLoc binder_name) $
+ (if theres_a_signature then
+ returnNF_Tc sig_tau -- Non-overloaded signature; use its type
+ else
+ newTyVarTy kind -- No signature; use a new type variable
+ ) `thenNF_Tc` \ mono_id_ty ->
+
+ newLocalId (getOccName binder_name) mono_id_ty `thenNF_Tc` \ mono_id ->
+ returnNF_Tc (emptyLIE, mono_id)
+ where
+ maybe_sig = maybeSig tc_ty_sigs binder_name
+ theres_a_signature = maybeToBool maybe_sig
+ Just (TySigInfo name poly_id sig_tyvars sig_theta sig_tau sig_loc) = maybe_sig
tysig_names = [name | (TySigInfo name _ _ _ _ _) <- tc_ty_sigs]
is_unrestricted = isUnRestrictedGroup tysig_names mbind
- kind | is_rec = mkBoxedTypeKind -- Recursive, so no unboxed types
- | otherwise = mkTypeKind -- Non-recursive, so we permit unboxed types
-
-zonk_theta theta = mapNF_Tc zonk theta
- where
- zonk (c,t) = zonkTcType t `thenNF_Tc` \ t' ->
- returnNF_Tc (c,t')
+ kind = case is_rec of
+ Recursive -> mkBoxedTypeKind -- Recursive, so no unboxed types
+ NonRecursive -> mkTypeKind -- Non-recursive, so we permit unboxed types
\end{code}
-@getImplicitStuffToGen@ decides what type variables generalise over.
+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 ins't being used (but that's a very common case).
+
+This can lead to a massive space leak, from the following top-level defn:
+
+ ff :: [Int] -> [Int]
+ ff = f 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.
+
+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. Thats' what the "mono_lies"
+is doing.
+
+
+%************************************************************************
+%* *
+\subsection{getTyVarsToGen}
+%* *
+%************************************************************************
+
+@getTyVarsToGen@ decides what type variables generalise over.
For a "restricted group" -- see the monomorphism restriction
for a definition -- we bind no dictionaries, and
find which tyvars are constrained.
\begin{code}
-getTyVarsToGen is_unrestricted mono_tyvars lie
- = tcGetGlobalTyVars `thenNF_Tc` \ free_tyvars ->
- zonkTcTyVars mono_tyvars `thenNF_Tc` \ mentioned_tyvars ->
+getTyVarsToGen is_unrestricted mono_id_tys lie
+ = tcGetGlobalTyVars `thenNF_Tc` \ free_tyvars ->
+ zonkTcTypes mono_id_tys `thenNF_Tc` \ zonked_mono_id_tys ->
let
- tyvars_to_gen = mentioned_tyvars `minusTyVarSet` free_tyvars
+ tyvars_to_gen = tyVarsOfTypes zonked_mono_id_tys `minusTyVarSet` free_tyvars
in
if is_unrestricted
then
returnTc (emptyTyVarSet, tyvars_to_gen)
else
- tcSimplify tyvars_to_gen lie `thenTc` \ (_, _, constrained_dicts) ->
+ tcSimplify (text "getTVG") NotTopLevel tyvars_to_gen lie `thenTc` \ (_, _, constrained_dicts) ->
let
-- ASSERT: dicts_sig is already zonked!
constrained_tyvars = foldrBag (unionTyVarSets . tyVarsOfInst) emptyTyVarSet constrained_dicts
tc_mono_binds bind@(PatMonoBind pat grhss_and_binds locn)
= tcAddSrcLoc locn $
+ tcAddErrCtxt (patMonoBindsCtxt bind) $
tcPat pat `thenTc` \ (pat2, lie_pat, pat_ty) ->
+
+ -- Before checking the RHS, but after the pattern, extend the envt with
+ -- bindings for the *polymorphic* Ids from any type signatures
tcExtendLocalValEnv sig_names sig_ids $
- tcGRHSsAndBinds grhss_and_binds `thenTc` \ (grhss_and_binds2, lie, grhss_ty) ->
- tcAddErrCtxt (patMonoBindsCtxt bind) $
- unifyTauTy pat_ty grhss_ty `thenTc_`
+ tcGRHSsAndBinds pat_ty grhss_and_binds `thenTc` \ (grhss_and_binds2, lie) ->
returnTc (PatMonoBind pat2 grhss_and_binds2 locn,
plusLIE lie_pat lie)
\end{code}
\begin{code}
data TcSigInfo s
- = TySigInfo Name
- (TcIdBndr s) -- *Polymorphic* binder for this value...
- [TcTyVar s] (TcThetaType s) (TcTauType s)
- SrcLoc
+ = TySigInfo
+ Name -- N, the Name in corresponding binding
+ (TcIdBndr s) -- *Polymorphic* binder for this value...
+ -- Usually has name = N, but doesn't have to.
+ [TcTyVar s]
+ (TcThetaType s)
+ (TcTauType s)
+ SrcLoc
maybeSig :: [TcSigInfo s] -> Name -> Maybe (TcSigInfo s)
tcTySig prag_info_fn (Sig v ty src_loc)
= tcAddSrcLoc src_loc $
tcHsType ty `thenTc` \ sigma_ty ->
- tcInstSigType sigma_ty `thenNF_Tc` \ sigma_ty' ->
+
+ -- Convert from Type to TcType
+ tcInstSigType sigma_ty `thenNF_Tc` \ sigma_tc_ty ->
+ let
+ poly_id = mkUserId v sigma_tc_ty (prag_info_fn v)
+ in
+ -- Instantiate this type
+ -- It's important to do this even though in the error-free case
+ -- we could just split the sigma_tc_ty (since the tyvars don't
+ -- unified with anything). But in the case of an error, when
+ -- the tyvars *do* get unified with something, we want to carry on
+ -- typechecking the rest of the program with the function bound
+ -- to a pristine type, namely sigma_tc_ty
+ tcInstSigTcType sigma_tc_ty `thenNF_Tc` \ (tyvars, rho) ->
let
- poly_id = mkUserId v sigma_ty' (prag_info_fn v)
- (tyvars', theta', tau') = splitSigmaTy sigma_ty'
+ (theta, tau) = splitRhoTy rho
-- This splitSigmaTy tries hard to make sure that tau' is a type synonym
-- wherever possible, which can improve interface files.
in
- returnTc (TySigInfo v poly_id tyvars' theta' tau' src_loc)
+ returnTc (TySigInfo v poly_id tyvars theta tau src_loc)
\end{code}
@checkSigMatch@ does the next step in checking signature matching.
tcAddErrCtxt (sigCtxt id) $
checkSigTyVars sig_tyvars sig_tau
- mk_dict_tys theta = [mkDictTy c t | (c,t) <- theta]
+ mk_dict_tys theta = [mkDictTy c ts | (c,ts) <- theta]
\end{code}
eg matching signature [(a,b)] against inferred type [(p,p)]
[then a and b will be unified together]
-BUT ACTUALLY THESE FIRST TWO ARE FORCED BY USING DontBind TYVARS
-
(c) not mentioned in the environment
eg the signature for f in this:
Before doing this, the substitution is applied to the signature type variable.
+We used to have the notion of a "DontBind" type variable, which would
+only be bound to itself or nothing. Then points (a) and (b) were
+self-checking. But it gave rise to bogus consequential error messages.
+For example:
+
+ f = (*) -- Monomorphic
+
+ g :: Num a => a -> a
+ g x = f x x
+
+Here, we get a complaint when checking the type signature for g,
+that g isn't polymorphic enough; but then we get another one when
+dealing with the (Num x) context arising from f's definition;
+we try to unify x with Int (to default it), but find that x has already
+been unified with the DontBind variable "a" from g's signature.
+This is really a problem with side-effecting unification; we'd like to
+undo g's effects when its type signature fails, but unification is done
+by side effect, so we can't (easily).
+
+So we revert to ordinary type variables for signatures, and try to
+give a helpful message in checkSigTyVars.
+
\begin{code}
checkSigTyVars :: [TcTyVar s] -- The original signature type variables
-> TcType s -- signature type (for err msg)
- -> TcM s ()
+ -> TcM s [TcTyVar s] -- Zonked signature type variables
checkSigTyVars sig_tyvars sig_tau
- = tcGetGlobalTyVars `thenNF_Tc` \ globals ->
+ = mapNF_Tc zonkTcTyVar sig_tyvars `thenNF_Tc` \ sig_tys ->
let
- mono_tyvars = filter (`elementOfTyVarSet` globals) sig_tyvars
+ sig_tyvars' = map (getTyVar "checkSigTyVars") sig_tys
in
- -- TEMPORARY FIX
- -- Until the final Bind-handling stuff is in, several type signatures in the same
- -- bindings group can cause the signature type variable from the different
- -- signatures to be unified. So we still need to zonk and check point (b).
- -- Remove when activating the new binding code
- mapNF_Tc zonkTcTyVar sig_tyvars `thenNF_Tc` \ sig_tys ->
- checkTcM (hasNoDups (map (getTyVar "checkSigTyVars") sig_tys))
+
+ -- Check points (a) and (b)
+ checkTcM (all isTyVarTy sig_tys && hasNoDups sig_tyvars')
(zonkTcType sig_tau `thenNF_Tc` \ sig_tau' ->
- failTc (badMatchErr sig_tau sig_tau')
+ failWithTc (badMatchErr sig_tau sig_tau')
) `thenTc_`
-
-- Check point (c)
-- We want to report errors in terms of the original signature tyvars,
- -- ie sig_tyvars, NOT sig_tyvars'. sig_tys and sig_tyvars' correspond
+ -- ie sig_tyvars, NOT sig_tyvars'. sig_tyvars' correspond
-- 1-1 with sig_tyvars, so we can just map back.
- checkTc (null mono_tyvars)
- (notAsPolyAsSigErr sig_tau mono_tyvars)
+ tcGetGlobalTyVars `thenNF_Tc` \ globals ->
+ let
+ mono_tyvars' = [sig_tv' | sig_tv' <- sig_tyvars',
+ sig_tv' `elementOfTyVarSet` globals]
+
+ mono_tyvars = map (assoc "checkSigTyVars" (sig_tyvars' `zip` sig_tyvars)) mono_tyvars'
+ in
+ checkTcM (null mono_tyvars')
+ (failWithTc (notAsPolyAsSigErr sig_tau mono_tyvars)) `thenTc_`
+
+ returnTc sig_tyvars'
\end{code}
\begin{code}
tcPragmaSigs :: [RenamedSig] -- The pragma signatures
-> TcM s (Name -> PragmaInfo, -- Maps name to the appropriate PragmaInfo
- TcHsBinds s,
+ TcMonoBinds s,
LIE s)
-- For now we just deal with INLINE pragmas
-tcPragmaSigs sigs = returnTc (prag_fn, EmptyBinds, emptyLIE )
+tcPragmaSigs sigs = returnTc (prag_fn, EmptyMonoBinds, emptyLIE )
where
prag_fn name | any has_inline sigs = IWantToBeINLINEd
| otherwise = NoPragmaInfo
Here are the easy cases for tcPragmaSigs
\begin{code}
-tcPragmaSig (DeforestSig name loc)
- = returnTc ((name, addDeforestInfo DoDeforest),EmptyBinds,emptyLIE)
tcPragmaSig (InlineSig name loc)
= returnTc ((name, addUnfoldInfo (iWantToBeINLINEd UnfoldAlways)), EmptyBinds, emptyLIE)
tcPragmaSig (MagicUnfoldingSig name string loc)
tcLookupLocalValueOK "tcPragmaSig" name `thenNF_Tc` \ main_id ->
tcInstSigType [] (idType main_id) `thenNF_Tc` \ main_ty ->
let
- (main_tyvars, main_rho) = splitForAllTy main_ty
+ (main_tyvars, main_rho) = splitForAllTys main_ty
(main_theta,main_tau) = splitRhoTy main_rho
main_arg_tys = mkTyVarTys main_tyvars
in
-- 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
- mapTc zonkTcType main_arg_tys `thenNF_Tc` \ main_arg_tys' ->
+ zonkTcTypes main_arg_tys `thenNF_Tc` \ main_arg_tys' ->
zonkTcThetaType main_theta `thenNF_Tc` \ main_theta' ->
tcAddErrCtxt (specGroundnessCtxt main_arg_tys')
(checkTc (all isGroundOrTyVarTy main_arg_tys')) `thenTc_`
\begin{code}
-patMonoBindsCtxt bind sty
- = hang (ptext SLIT("In a pattern binding:")) 4 (ppr sty bind)
+patMonoBindsCtxt bind
+ = hang (ptext SLIT("In a pattern binding:")) 4 (ppr bind)
-----------------------------------------------
-valSpecSigCtxt v ty sty
- = hang (ptext SLIT("In a SPECIALIZE pragma for a value:"))
- 4 (sep [(<>) (ppr sty v) (ptext SLIT(" ::")),
- ppr sty ty])
-
-
+valSpecSigCtxt v ty
+ = sep [ptext SLIT("In a SPECIALIZE pragma for a value:"),
+ nest 4 (ppr v <+> ptext SLIT(" ::") <+> ppr ty)]
-----------------------------------------------
-notAsPolyAsSigErr sig_tau mono_tyvars sty
+notAsPolyAsSigErr sig_tau mono_tyvars
= hang (ptext SLIT("A type signature is more polymorphic than the inferred type"))
- 4 (vcat [text "Some type variables in the inferred type can't be forall'd, namely:",
- interpp'SP sty mono_tyvars,
- ptext SLIT("Possible cause: the RHS mentions something subject to the monomorphism restriction")
- ])
+ 4 (vcat [text "Can't for-all the type variable(s)" <+>
+ pprQuotedList mono_tyvars,
+ text "in the type" <+> quotes (ppr sig_tau)
+ ])
-----------------------------------------------
-badMatchErr sig_ty inferred_ty sty
+badMatchErr sig_ty inferred_ty
= hang (ptext SLIT("Type signature doesn't match inferred type"))
- 4 (vcat [hang (ptext SLIT("Signature:")) 4 (ppr sty sig_ty),
- hang (ptext SLIT("Inferred :")) 4 (ppr sty inferred_ty)
+ 4 (vcat [hang (ptext SLIT("Signature:")) 4 (ppr sig_ty),
+ hang (ptext SLIT("Inferred :")) 4 (ppr inferred_ty)
])
-----------------------------------------------
-sigCtxt id sty
- = sep [ptext SLIT("When checking signature for"), ppr sty id]
-sigsCtxt ids sty
- = sep [ptext SLIT("When checking signature(s) for:"), interpp'SP sty ids]
+sigCtxt id
+ = sep [ptext SLIT("When checking the type signature for"), quotes (ppr id)]
+
+bindSigsCtxt ids
+ = ptext SLIT("When checking the type signature(s) for") <+> pprQuotedList ids
-----------------------------------------------
-sigContextsErr sty
+sigContextsErr
= ptext SLIT("Mismatched contexts")
-sigContextsCtxt s1 s2 sty
+sigContextsCtxt s1 s2
= hang (hsep [ptext SLIT("When matching the contexts of the signatures for"),
- ppr sty s1, ptext SLIT("and"), ppr sty s2])
+ quotes (ppr s1), ptext SLIT("and"), quotes (ppr s2)])
4 (ptext SLIT("(the signature contexts in a mutually recursive group should all be identical)"))
-----------------------------------------------
= panic "specGroundnessCtxt"
--------------------------------------------
-specContextGroundnessCtxt -- err_ctxt dicts sty
+specContextGroundnessCtxt -- err_ctxt dicts
= panic "specContextGroundnessCtxt"
{-
= hang (
- sep [hsep [ptext SLIT("In the SPECIALIZE pragma for"), ppr sty name],
- hcat [ptext SLIT(" specialised to the type"), ppr sty spec_ty],
- pp_spec_id sty,
+ sep [hsep [ptext SLIT("In the SPECIALIZE pragma for"), ppr name],
+ hcat [ptext SLIT(" specialised to the type"), ppr spec_ty],
+ pp_spec_id,
ptext SLIT("... not all overloaded type variables were instantiated"),
ptext SLIT("to ground types:")])
- 4 (vcat [hsep [ppr sty c, ppr sty t]
+ 4 (vcat [hsep [ppr c, ppr t]
| (c,t) <- map getDictClassAndType dicts])
where
(name, spec_ty, locn, pp_spec_id)
ValSpecSigCtxt n ty loc -> (n, ty, loc, \ x -> empty)
ValSpecSpecIdCtxt n ty spec loc ->
(n, ty, loc,
- \ sty -> hsep [ptext SLIT("... type of explicit id"), ppr sty spec])
+ hsep [ptext SLIT("... type of explicit id"), ppr spec])
-}
\end{code}
-
-
-
-
projects / ghc-hetmet.git / blobdiff