%
+% (c) The University of Glasgow 2006
% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
\section[TcExpr]{Typecheck an expression}
\begin{code}
-module TcExpr ( tcPolyExpr, tcPolyExprNC,
- tcMonoExpr, tcInferRho, tcSyntaxOp ) where
+{-# OPTIONS -w #-}
+-- The above warning supression flag is a temporary kludge.
+-- While working on this module you are encouraged to remove it and fix
+-- any warnings in the module. See
+-- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
+-- for details
+
+module TcExpr ( tcPolyExpr, tcPolyExprNC, tcMonoExpr, tcMonoExprNC,
+ tcInferRho, tcInferRhoNC, tcSyntaxOp,
+ addExprErrCtxt ) where
#include "HsVersions.h"
#ifdef GHCI /* Only if bootstrapped */
import {-# SOURCE #-} TcSplice( tcSpliceExpr, tcBracket )
-import HsSyn ( nlHsVar )
-import Id ( Id )
-import Name ( isExternalName )
-import TcType ( isTauTy )
-import TcEnv ( checkWellStaged )
-import HsSyn ( nlHsApp )
import qualified DsMeta
#endif
-import HsSyn ( HsExpr(..), LHsExpr, ArithSeqInfo(..), recBindFields,
- HsMatchContext(..), HsRecordBinds,
- mkHsCoerce, mkHsApp, mkHsDictApp, mkHsTyApp )
-import TcHsSyn ( hsLitType )
+import HsSyn
+import TcHsSyn
import TcRnMonad
-import TcUnify ( tcInfer, tcSubExp, tcFunResTy, tcGen, boxyUnify, subFunTys, zapToMonotype, stripBoxyType,
- boxySplitListTy, boxySplitTyConApp, wrapFunResCoercion, preSubType,
- unBox )
-import BasicTypes ( Arity, isMarkedStrict )
-import Inst ( newMethodFromName, newIPDict, instToId,
- newDicts, newMethodWithGivenTy, tcInstStupidTheta )
-import TcBinds ( tcLocalBinds )
-import TcEnv ( tcLookup, tcLookupId, tcLookupDataCon, tcLookupField )
-import TcArrows ( tcProc )
-import TcMatches ( tcMatchesCase, tcMatchLambda, tcDoStmts, TcMatchCtxt(..) )
-import TcHsType ( tcHsSigType, UserTypeCtxt(..) )
-import TcPat ( tcOverloadedLit, badFieldCon )
-import TcMType ( tcInstTyVars, newFlexiTyVarTy, newBoxyTyVars, readFilledBox, zonkTcTypes )
-import TcType ( TcType, TcSigmaType, TcRhoType,
- BoxySigmaType, BoxyRhoType, ThetaType,
- mkTyVarTys, mkFunTys,
- tcMultiSplitSigmaTy, tcSplitFunTysN, tcSplitTyConApp_maybe,
- isSigmaTy, mkFunTy, mkTyConApp, isLinearPred,
- exactTyVarsOfType, exactTyVarsOfTypes,
- zipTopTvSubst, zipOpenTvSubst, substTys, substTyVar
- )
-import Kind ( argTypeKind )
-
-import Id ( Id, idType, idName, recordSelectorFieldLabel,
- isRecordSelector, isNaughtyRecordSelector, isDataConId_maybe )
-import DataCon ( DataCon, dataConFieldLabels, dataConStrictMarks, dataConSourceArity,
- dataConWrapId, isVanillaDataCon, dataConTyVars, dataConOrigArgTys )
-import Name ( Name )
-import TyCon ( FieldLabel, tyConStupidTheta, tyConDataCons, isEnumerationTyCon )
-import Type ( substTheta, substTy )
-import Var ( TyVar, tyVarKind )
-import VarSet ( emptyVarSet, elemVarSet, unionVarSet )
-import TysWiredIn ( boolTy, parrTyCon, tupleTyCon )
-import PrelNames ( enumFromName, enumFromThenName,
- enumFromToName, enumFromThenToName,
- enumFromToPName, enumFromThenToPName, negateName,
- hasKey
- )
-import PrimOp ( tagToEnumKey )
-
+import TcUnify
+import BasicTypes
+import Inst
+import TcBinds
+import TcEnv
+import TcArrows
+import TcMatches
+import TcHsType
+import TcPat
+import TcMType
+import TcType
+import TcIface ( checkWiredInTyCon )
+import Id
+import DataCon
+import Name
+import TyCon
+import Type
+import TypeRep
+import Coercion
+import Var
+import VarSet
+import TysWiredIn
+import PrelNames
+import PrimOp
import DynFlags
-import StaticFlags ( opt_NoMethodSharing )
-import HscTypes ( TyThing(..) )
-import SrcLoc ( Located(..), unLoc, noLoc, getLoc )
+import StaticFlags
+import HscTypes
+import SrcLoc
import Util
-import ListSetOps ( assocMaybe )
-import Maybes ( catMaybes )
+import ListSetOps
+import Maybes
import Outputable
import FastString
-#ifdef DEBUG
-import TyCon ( tyConArity )
-#endif
+import Data.List( partition )
+import Control.Monad
\end{code}
%************************************************************************
-- to do so himself.
tcPolyExpr expr res_ty
- = addErrCtxt (exprCtxt (unLoc expr)) $
- tcPolyExprNC expr res_ty
+ = addExprErrCtxt expr $
+ (do {traceTc (text "tcPolyExpr") ; tcPolyExprNC expr res_ty })
tcPolyExprNC expr res_ty
| isSigmaTy res_ty
- = do { (gen_fn, expr') <- tcGen res_ty emptyVarSet (tcPolyExprNC expr)
+ = do { traceTc (text "tcPolyExprNC" <+> ppr res_ty)
+ ; (gen_fn, expr') <- tcGen res_ty emptyVarSet Nothing $ \ _ res_ty ->
+ tcPolyExprNC expr res_ty
-- Note the recursive call to tcPolyExpr, because the
-- type may have multiple layers of for-alls
- ; return (L (getLoc expr') (mkHsCoerce gen_fn (unLoc expr'))) }
+ -- E.g. forall a. Eq a => forall b. Ord b => ....
+ ; return (mkLHsWrap gen_fn expr') }
| otherwise
- = tcMonoExpr expr res_ty
+ = tcMonoExprNC expr res_ty
---------------
tcPolyExprs :: [LHsExpr Name] -> [TcType] -> TcM [LHsExpr TcId]
-tcPolyExprs [] [] = returnM []
+tcPolyExprs [] [] = return []
tcPolyExprs (expr:exprs) (ty:tys)
= do { expr' <- tcPolyExpr expr ty
; exprs' <- tcPolyExprs exprs tys
- ; returnM (expr':exprs') }
+ ; return (expr':exprs') }
tcPolyExprs exprs tys = pprPanic "tcPolyExprs" (ppr exprs $$ ppr tys)
---------------
-tcMonoExpr :: LHsExpr Name -- Expression to type check
- -> BoxyRhoType -- Expected type (could be a type variable)
- -- Definitely no foralls at the top
- -- Can contain boxes, which will be filled in
- -> TcM (LHsExpr TcId)
-
-tcMonoExpr (L loc expr) res_ty
+tcMonoExpr, tcMonoExprNC
+ :: LHsExpr Name -- Expression to type check
+ -> BoxyRhoType -- Expected type (could be a type variable)
+ -- Definitely no foralls at the top
+ -- Can contain boxes, which will be filled in
+ -> TcM (LHsExpr TcId)
+
+tcMonoExpr expr res_ty
+ = addErrCtxt (exprCtxt expr) $
+ tcMonoExprNC expr res_ty
+
+tcMonoExprNC (L loc expr) res_ty
= ASSERT( not (isSigmaTy res_ty) )
setSrcSpan loc $
do { expr' <- tcExpr expr res_ty
; return (L loc expr') }
---------------
-tcInferRho :: LHsExpr Name -> TcM (LHsExpr TcId, TcRhoType)
-tcInferRho expr = tcInfer (tcMonoExpr expr)
+tcInferRho, tcInferRhoNC :: LHsExpr Name -> TcM (LHsExpr TcId, TcRhoType)
+tcInferRho expr = tcInfer (tcMonoExpr expr)
+tcInferRhoNC expr = tcInfer (tcMonoExprNC expr)
\end{code}
-
%************************************************************************
%* *
tcExpr: the main expression typechecker
\begin{code}
tcExpr :: HsExpr Name -> BoxyRhoType -> TcM (HsExpr TcId)
+tcExpr e res_ty | debugIsOn && isSigmaTy res_ty -- Sanity check
+ = pprPanic "tcExpr: sigma" (ppr res_ty $$ ppr e)
+
tcExpr (HsVar name) res_ty = tcId (OccurrenceOf name) name res_ty
-tcExpr (HsLit lit) res_ty = do { boxyUnify (hsLitType lit) res_ty
- ; return (HsLit lit) }
+tcExpr (HsLit lit) res_ty = do { let lit_ty = hsLitType lit
+ ; coi <- boxyUnify lit_ty res_ty
+ ; return $ mkHsWrapCoI coi (HsLit lit)
+ }
-tcExpr (HsPar expr) res_ty = do { expr' <- tcMonoExpr expr res_ty
+tcExpr (HsPar expr) res_ty = do { expr' <- tcMonoExprNC expr res_ty
; return (HsPar expr') }
tcExpr (HsSCC lbl expr) res_ty = do { expr' <- tcMonoExpr expr res_ty
- ; returnM (HsSCC lbl expr') }
+ ; return (HsSCC lbl expr') }
+tcExpr (HsTickPragma info expr) res_ty
+ = do { expr' <- tcMonoExpr expr res_ty
+ ; return (HsTickPragma info expr') }
tcExpr (HsCoreAnn lbl expr) res_ty -- hdaume: core annotation
= do { expr' <- tcMonoExpr expr res_ty
; return (HsOverLit lit') }
tcExpr (NegApp expr neg_expr) res_ty
- = do { neg_expr' <- tcSyntaxOp (OccurrenceOf negateName) neg_expr
+ = do { neg_expr' <- tcSyntaxOp NegateOrigin neg_expr
(mkFunTy res_ty res_ty)
; expr' <- tcMonoExpr expr res_ty
; return (NegApp expr' neg_expr') }
tcExpr (HsIPVar ip) res_ty
- = do { -- Implicit parameters must have a *tau-type* not a
+ = do { let origin = IPOccOrigin ip
+ -- Implicit parameters must have a *tau-type* not a
-- type scheme. We enforce this by creating a fresh
-- type variable as its type. (Because res_ty may not
-- be a tau-type.)
- ip_ty <- newFlexiTyVarTy argTypeKind -- argTypeKind: it can't be an unboxed tuple
- ; co_fn <- tcSubExp ip_ty res_ty
- ; (ip', inst) <- newIPDict (IPOccOrigin ip) ip ip_ty
+ ; ip_ty <- newFlexiTyVarTy argTypeKind -- argTypeKind: it can't be an unboxed tuple
+ ; co_fn <- tcSubExp origin ip_ty res_ty
+ ; (ip', inst) <- newIPDict origin ip ip_ty
; extendLIE inst
- ; return (mkHsCoerce co_fn (HsIPVar ip')) }
+ ; return (mkHsWrap co_fn (HsIPVar ip')) }
tcExpr (HsApp e1 e2) res_ty
= go e1 [e2]
go lfun@(L loc fun) args
= do { (fun', args') <- -- addErrCtxt (callCtxt lfun args) $
tcApp fun (length args) (tcArgs lfun args) res_ty
+ ; traceTc (text "tcExpr args': " <+> ppr args')
; return (unLoc (foldl mkHsApp (L loc fun') args')) }
tcExpr (HsLam match) res_ty
= do { (co_fn, match') <- tcMatchLambda match res_ty
- ; return (mkHsCoerce co_fn (HsLam match')) }
+ ; return (mkHsWrap co_fn (HsLam match')) }
tcExpr in_expr@(ExprWithTySig expr sig_ty) res_ty
= do { sig_tc_ty <- tcHsSigType ExprSigCtxt sig_ty
- ; expr' <- tcPolyExpr expr sig_tc_ty
- ; co_fn <- tcSubExp sig_tc_ty res_ty
- ; return (mkHsCoerce co_fn (ExprWithTySigOut expr' sig_ty)) }
+
+ -- Remember to extend the lexical type-variable environment
+ ; (gen_fn, expr') <- tcGen sig_tc_ty emptyVarSet (Just ExprSigCtxt) $ \ skol_tvs res_ty ->
+ tcExtendTyVarEnv2 (hsExplicitTvs sig_ty `zip` mkTyVarTys skol_tvs) $
+ -- See Note [More instantiated than scoped] in TcBinds
+ tcMonoExprNC expr res_ty
+
+ ; co_fn <- tcSubExp ExprSigOrigin sig_tc_ty res_ty
+ ; return (mkHsWrap co_fn (ExprWithTySigOut (mkLHsWrap gen_fn expr') sig_ty)) }
tcExpr (HsType ty) res_ty
= failWithTc (text "Can't handle type argument:" <+> ppr ty)
-- \ x -> e op x,
-- or
-- \ x -> op e x,
--- or just
+-- or, if PostfixOperators is enabled, just
-- op e
--
--- We treat it as similar to the latter, so we don't
+-- With PostfixOperators we don't
-- actually require the function to take two arguments
-- at all. For example, (x `not`) means (not x);
--- you get postfix operators! Not really Haskell 98
--- I suppose, but it's less work and kind of useful.
+-- you get postfix operators! Not Haskell 98,
+-- but it's less work and kind of useful.
tcExpr in_expr@(SectionL arg1 lop@(L loc op)) res_ty
- = do { (op', [arg1']) <- tcApp op 1 (tcArgs lop [arg1]) res_ty
- ; return (SectionL arg1' (L loc op')) }
+ = do { dflags <- getDOpts
+ ; if dopt Opt_PostfixOperators dflags
+ then do { (op', [arg1']) <- tcApp op 1 (tcArgs lop [arg1]) res_ty
+ ; return (SectionL arg1' (L loc op')) }
+ else do
+ { (co_fn, expr')
+ <- subFunTys doc 1 res_ty Nothing $ \ [arg2_ty'] res_ty' ->
+ do { (op', (arg1', co_arg2)) <- tcApp op 2 (tc_args arg2_ty') res_ty'
+ ; let coi = mkFunTyCoI arg2_ty' co_arg2 res_ty' IdCo
+ ; return (mkHsWrapCoI coi (SectionL arg1' (L loc op'))) }
+ ; return (mkHsWrap co_fn expr') } }
+ where
+ doc = ptext (sLit "The section") <+> quotes (ppr in_expr)
+ <+> ptext (sLit "takes one argument")
+ tc_args arg2_ty' qtvs qtys [arg1_ty, arg2_ty]
+ = do { co_arg2 <- boxyUnify (substTyWith qtvs qtys arg2_ty) arg2_ty'
+ ; arg1' <- tcArg lop 1 arg1 qtvs qtys arg1_ty
+ ; qtys' <- mapM refineBox qtys -- c.f. tcArgs
+ ; return (qtys', (arg1', co_arg2)) }
+ tc_args _ _ _ _ = panic "tcExpr SectionL"
-- Right sections, equivalent to \ x -> x `op` expr, or
-- \ x -> op x expr
tcExpr in_expr@(SectionR lop@(L loc op) arg2) res_ty
- = do { (co_fn, (op', arg2')) <- subFunTys doc 1 res_ty $ \ [arg1_ty'] res_ty' ->
- tcApp op 2 (tc_args arg1_ty') res_ty'
- ; return (mkHsCoerce co_fn (SectionR (L loc op') arg2')) }
+ = do { (co_fn, expr')
+ <- subFunTys doc 1 res_ty Nothing $ \ [arg1_ty'] res_ty' ->
+ do { (op', (co_arg1, arg2')) <- tcApp op 2 (tc_args arg1_ty') res_ty'
+ ; let coi = mkFunTyCoI arg1_ty' co_arg1 res_ty' IdCo
+ ; return (mkHsWrapCoI coi $ SectionR (L loc op') arg2') }
+ ; return (mkHsWrap co_fn expr') }
where
- doc = ptext SLIT("The section") <+> quotes (ppr in_expr)
- <+> ptext SLIT("takes one argument")
- tc_args arg1_ty' [arg1_ty, arg2_ty]
- = do { boxyUnify arg1_ty' arg1_ty
- ; tcArg lop (arg2, arg2_ty, 2) }
- tc_args arg1_ty' other = panic "tcExpr SectionR"
+ doc = ptext (sLit "The section") <+> quotes (ppr in_expr)
+ <+> ptext (sLit "takes one argument")
+ tc_args arg1_ty' qtvs qtys [arg1_ty, arg2_ty]
+ = do { co_arg1 <- boxyUnify (substTyWith qtvs qtys arg1_ty) arg1_ty'
+ ; arg2' <- tcArg lop 2 arg2 qtvs qtys arg2_ty
+ ; qtys' <- mapM refineBox qtys -- c.f. tcArgs
+ ; return (qtys', (co_arg1, arg2')) }
+ tc_args arg1_ty' _ _ _ = panic "tcExpr SectionR"
+
+-- For tuples, take care to preserve rigidity
+-- E.g. case (x,y) of ....
+-- The scrutinee should have a rigid type if x,y do
+-- The general scheme is the same as in tcIdApp
+tcExpr in_expr@(ExplicitTuple tup_args boxity) res_ty
+ = do { let kind = case boxity of { Boxed -> liftedTypeKind
+ ; Unboxed -> argTypeKind }
+ arity = length tup_args
+ tup_tc = tupleTyCon boxity arity
+ mk_tup_res_ty arg_tys
+ = mkFunTys [ty | (ty, Missing _) <- arg_tys `zip` tup_args]
+ (mkTyConApp tup_tc arg_tys)
+
+ ; checkWiredInTyCon tup_tc -- Ensure instances are available
+ ; tvs <- newBoxyTyVars (replicate arity kind)
+ ; let arg_tys1 = map mkTyVarTy tvs
+ ; arg_tys2 <- preSubType tvs (mkVarSet tvs) (mk_tup_res_ty arg_tys1) res_ty
+
+ ; let go (Missing _, arg_ty) = return (Missing arg_ty)
+ go (Present expr, arg_ty) = do { expr' <- tcPolyExpr expr arg_ty
+ ; return (Present expr') }
+ ; tup_args' <- mapM go (tup_args `zip` arg_tys2)
+
+ ; arg_tys3 <- mapM refineBox arg_tys2
+ ; co_fn <- tcSubExp TupleOrigin (mk_tup_res_ty arg_tys3) res_ty
+ ; return (mkHsWrap co_fn (ExplicitTuple tup_args' boxity)) }
\end{code}
\begin{code}
--
-- But now, in the GADT world, we need to typecheck the scrutinee
-- first, to get type info that may be refined in the case alternatives
- (scrut', scrut_ty) <- addErrCtxt (caseScrutCtxt scrut)
- (tcInferRho scrut)
+ (scrut', scrut_ty) <- tcInferRho scrut
; traceTc (text "HsCase" <+> ppr scrut_ty)
; matches' <- tcMatchesCase match_ctxt scrut_ty matches exp_ty
; return (HsCase scrut' matches') }
where
match_ctxt = MC { mc_what = CaseAlt,
- mc_body = tcPolyExpr }
+ mc_body = tcBody }
tcExpr (HsIf pred b1 b2) res_ty
- = do { pred' <- addErrCtxt (predCtxt pred) $
- tcMonoExpr pred boolTy
+ = do { pred' <- tcMonoExpr pred boolTy
; b1' <- tcMonoExpr b1 res_ty
; b2' <- tcMonoExpr b2 res_ty
; return (HsIf pred' b1' b2') }
tcExpr (HsDo do_or_lc stmts body _) res_ty
= tcDoStmts do_or_lc stmts body res_ty
-tcExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
- = do { elt_ty <- boxySplitListTy res_ty
- ; exprs' <- mappM (tc_elt elt_ty) exprs
- ; return (ExplicitList elt_ty exprs') }
+tcExpr in_expr@(ExplicitList _ exprs) res_ty
+ = do { (elt_ty, coi) <- boxySplitListTy res_ty
+ ; exprs' <- mapM (tc_elt elt_ty) exprs
+ ; when (null exprs) (zapToMonotype elt_ty >> return ())
+ -- If there are no expressions in the comprehension
+ -- we must still fill in the box
+ --
+ -- The GHC front end never generates an empty ExplicitList
+ -- (instead it generates the [] data constructor) but
+ -- Template Haskell might. We could fix the bit of
+ -- TH that generates ExplicitList, but it seems less
+ -- fragile to just handle the case here.
+ ; return $ mkHsWrapCoI coi (ExplicitList elt_ty exprs') }
where
tc_elt elt_ty expr = tcPolyExpr expr elt_ty
tcExpr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
- = do { [elt_ty] <- boxySplitTyConApp parrTyCon res_ty
- ; exprs' <- mappM (tc_elt elt_ty) exprs
- ; ifM (null exprs) (zapToMonotype elt_ty)
+ = do { (elt_ty, coi) <- boxySplitPArrTy res_ty
+ ; exprs' <- mapM (tc_elt elt_ty) exprs
+ ; when (null exprs) (zapToMonotype elt_ty >> return ())
-- If there are no expressions in the comprehension
-- we must still fill in the box
-- (Not needed for [] and () becuase they happen
-- to parse as data constructors.)
- ; return (ExplicitPArr elt_ty exprs') }
+ ; return $ mkHsWrapCoI coi (ExplicitPArr elt_ty exprs') }
where
tc_elt elt_ty expr = tcPolyExpr expr elt_ty
-tcExpr (ExplicitTuple exprs boxity) res_ty
- = do { arg_tys <- boxySplitTyConApp (tupleTyCon boxity (length exprs)) res_ty
- ; exprs' <- tcPolyExprs exprs arg_tys
- ; return (ExplicitTuple exprs' boxity) }
-
tcExpr (HsProc pat cmd) res_ty
- = do { (pat', cmd') <- tcProc pat cmd res_ty
- ; return (HsProc pat' cmd') }
+ = do { (pat', cmd', coi) <- tcProc pat cmd res_ty
+ ; return $ mkHsWrapCoI coi (HsProc pat' cmd') }
tcExpr e@(HsArrApp _ _ _ _ _) _
- = failWithTc (vcat [ptext SLIT("The arrow command"), nest 2 (ppr e),
- ptext SLIT("was found where an expression was expected")])
+ = failWithTc (vcat [ptext (sLit "The arrow command"), nest 2 (ppr e),
+ ptext (sLit "was found where an expression was expected")])
tcExpr e@(HsArrForm _ _ _) _
- = failWithTc (vcat [ptext SLIT("The arrow command"), nest 2 (ppr e),
- ptext SLIT("was found where an expression was expected")])
+ = failWithTc (vcat [ptext (sLit "The arrow command"), nest 2 (ppr e),
+ ptext (sLit "was found where an expression was expected")])
\end{code}
%************************************************************************
; checkMissingFields data_con rbinds
; let arity = dataConSourceArity data_con
- check_fields arg_tys
- = do { rbinds' <- tcRecordBinds data_con arg_tys rbinds
- ; mapM unBox arg_tys
- ; return rbinds' }
- -- The unBox ensures that all the boxes in arg_tys are indeed
+ check_fields qtvs qtys arg_tys
+ = do { let arg_tys' = substTys (zipOpenTvSubst qtvs qtys) arg_tys
+ ; rbinds' <- tcRecordBinds data_con arg_tys' rbinds
+ ; qtys' <- mapM refineBoxToTau qtys
+ ; return (qtys', rbinds') }
+ -- The refineBoxToTau ensures that all the boxes in arg_tys are indeed
-- filled, which is the invariant expected by tcIdApp
+ -- How could this not be the case? Consider a record construction
+ -- that does not mention all the fields.
; (con_expr, rbinds') <- tcIdApp con_name arity check_fields res_ty
- ; returnM (RecordCon (L loc (dataConWrapId data_con)) con_expr rbinds') }
-
--- The main complication with RecordUpd is that we need to explicitly
--- handle the *non-updated* fields. Consider:
---
--- data T a b = MkT1 { fa :: a, fb :: b }
--- | MkT2 { fa :: a, fc :: Int -> Int }
--- | MkT3 { fd :: a }
---
--- upd :: T a b -> c -> T a c
--- upd t x = t { fb = x}
---
--- The type signature on upd is correct (i.e. the result should not be (T a b))
--- because upd should be equivalent to:
---
--- upd t x = case t of
--- MkT1 p q -> MkT1 p x
--- MkT2 a b -> MkT2 p b
--- MkT3 d -> error ...
---
--- So we need to give a completely fresh type to the result record,
--- and then constrain it by the fields that are *not* updated ("p" above).
---
--- Note that because MkT3 doesn't contain all the fields being updated,
--- its RHS is simply an error, so it doesn't impose any type constraints
---
--- All this is done in STEP 4 below.
---
--- Note about GADTs
--- ~~~~~~~~~~~~~~~~
--- For record update we require that every constructor involved in the
--- update (i.e. that has all the specified fields) is "vanilla". I
--- don't know how to do the update otherwise.
+ ; return (RecordCon (L loc (dataConWrapId data_con)) con_expr rbinds') }
+\end{code}
+Note [Type of a record update]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The main complication with RecordUpd is that we need to explicitly
+handle the *non-updated* fields. Consider:
-tcExpr expr@(RecordUpd record_expr rbinds _ _) res_ty
- = -- STEP 0
+ data T a b c = MkT1 { fa :: a, fb :: (b,c) }
+ | MkT2 { fa :: a, fb :: (b,c), fc :: c -> c }
+ | MkT3 { fd :: a }
+
+ upd :: T a b c -> (b',c) -> T a b' c
+ upd t x = t { fb = x}
+
+The result type should be (T a b' c)
+not (T a b c), because 'b' *is not* mentioned in a non-updated field
+not (T a b' c'), becuase 'c' *is* mentioned in a non-updated field
+NB that it's not good enough to look at just one constructor; we must
+look at them all; cf Trac #3219
+
+After all, upd should be equivalent to:
+ upd t x = case t of
+ MkT1 p q -> MkT1 p x
+ MkT2 a b -> MkT2 p b
+ MkT3 d -> error ...
+
+So we need to give a completely fresh type to the result record,
+and then constrain it by the fields that are *not* updated ("p" above).
+We call these the "fixed" type variables, and compute them in getFixedTyVars.
+
+Note that because MkT3 doesn't contain all the fields being updated,
+its RHS is simply an error, so it doesn't impose any type constraints.
+Hence the use of 'relevant_cont'.
+
+Note [Implict type sharing]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+We also take into account any "implicit" non-update fields. For example
+ data T a b where { MkT { f::a } :: T a a; ... }
+So the "real" type of MkT is: forall ab. (a~b) => a -> T a b
+
+Then consider
+ upd t x = t { f=x }
+We infer the type
+ upd :: T a b -> a -> T a b
+ upd (t::T a b) (x::a)
+ = case t of { MkT (co:a~b) (_:a) -> MkT co x }
+We can't give it the more general type
+ upd :: T a b -> c -> T c b
+
+Note [Criteria for update]
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+We want to allow update for existentials etc, provided the updated
+field isn't part of the existential. For example, this should be ok.
+ data T a where { MkT { f1::a, f2::b->b } :: T a }
+ f :: T a -> b -> T b
+ f t b = t { f1=b }
+
+The criterion we use is this:
+
+ The types of the updated fields
+ mention only the universally-quantified type variables
+ of the data constructor
+
+NB: this is not (quite) the same as being a "naughty" record selector
+(See Note [Naughty record selectors]) in TcTyClsDecls), at least
+in the case of GADTs. Consider
+ data T a where { MkT :: { f :: a } :: T [a] }
+Then f is not "naughty" because it has a well-typed record selector.
+But we don't allow updates for 'f'. (One could consider trying to
+allow this, but it makes my head hurt. Badly. And no one has asked
+for it.)
+
+In principle one could go further, and allow
+ g :: T a -> T a
+ g t = t { f2 = \x -> x }
+because the expression is polymorphic...but that seems a bridge too far.
+
+Note [Data family example]
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+ data instance T (a,b) = MkT { x::a, y::b }
+ --->
+ data :TP a b = MkT { a::a, y::b }
+ coTP a b :: T (a,b) ~ :TP a b
+
+Suppose r :: T (t1,t2), e :: t3
+Then r { x=e } :: T (t3,t1)
+ --->
+ case r |> co1 of
+ MkT x y -> MkT e y |> co2
+ where co1 :: T (t1,t2) ~ :TP t1 t2
+ co2 :: :TP t3 t2 ~ T (t3,t2)
+The wrapping with co2 is done by the constructor wrapper for MkT
+
+Outgoing invariants
+~~~~~~~~~~~~~~~~~~~
+In the outgoing (HsRecordUpd scrut binds cons in_inst_tys out_inst_tys):
+
+ * cons are the data constructors to be updated
+
+ * in_inst_tys, out_inst_tys have same length, and instantiate the
+ *representation* tycon of the data cons. In Note [Data
+ family example], in_inst_tys = [t1,t2], out_inst_tys = [t3,t2]
+
+\begin{code}
+tcExpr expr@(RecordUpd record_expr rbinds _ _ _) res_ty
+ = ASSERT( notNull upd_fld_names )
+ do {
+ -- STEP 0
-- Check that the field names are really field names
- ASSERT( notNull rbinds )
- let
- field_names = map fst rbinds
- in
- mappM (tcLookupField . unLoc) field_names `thenM` \ sel_ids ->
- -- The renamer has already checked that they
- -- are all in scope
- let
- bad_guys = [ setSrcSpan loc $ addErrTc (notSelector field_name)
- | (L loc field_name, sel_id) <- field_names `zip` sel_ids,
- not (isRecordSelector sel_id) -- Excludes class ops
- ]
- in
- checkM (null bad_guys) (sequenceM bad_guys `thenM_` failM) `thenM_`
+ ; sel_ids <- mapM tcLookupField upd_fld_names
+ -- The renamer has already checked that
+ -- selectors are all in scope
+ ; let bad_guys = [ setSrcSpan loc $ addErrTc (notSelector fld_name)
+ | (fld, sel_id) <- rec_flds rbinds `zip` sel_ids,
+ not (isRecordSelector sel_id), -- Excludes class ops
+ let L loc fld_name = hsRecFieldId fld ]
+ ; unless (null bad_guys) (sequence bad_guys >> failM)
-- STEP 1
-- Figure out the tycon and data cons from the first field name
- let
- -- It's OK to use the non-tc splitters here (for a selector)
- upd_field_lbls = recBindFields rbinds
- sel_id : _ = sel_ids
- (tycon, _) = recordSelectorFieldLabel sel_id -- We've failed already if
- data_cons = tyConDataCons tycon -- it's not a field label
- relevant_cons = filter is_relevant data_cons
- is_relevant con = all (`elem` dataConFieldLabels con) upd_field_lbls
- in
-
- -- STEP 2
- -- Check that at least one constructor has all the named fields
- -- i.e. has an empty set of bad fields returned by badFields
- checkTc (not (null relevant_cons))
- (badFieldsUpd rbinds) `thenM_`
-
- -- Check that all relevant data cons are vanilla. Doing record updates on
- -- GADTs and/or existentials is more than my tiny brain can cope with today
- checkTc (all isVanillaDataCon relevant_cons)
- (nonVanillaUpd tycon) `thenM_`
-
- -- STEP 4
- -- Use the un-updated fields to find a vector of booleans saying
- -- which type arguments must be the same in updatee and result.
- --
- -- WARNING: this code assumes that all data_cons in a common tycon
- -- have FieldLabels abstracted over the same tyvars.
- let
+ ; let -- It's OK to use the non-tc splitters here (for a selector)
+ sel_id : _ = sel_ids
+ (tycon, _) = recordSelectorFieldLabel sel_id -- We've failed already if
+ data_cons = tyConDataCons tycon -- it's not a field label
+ -- NB: for a data type family, the tycon is the instance tycon
+
+ relevant_cons = filter is_relevant data_cons
+ is_relevant con = all (`elem` dataConFieldLabels con) upd_fld_names
-- A constructor is only relevant to this process if
-- it contains *all* the fields that are being updated
- con1 = head relevant_cons -- A representative constructor
- con1_tyvars = dataConTyVars con1
- con1_flds = dataConFieldLabels con1
- con1_arg_tys = dataConOrigArgTys con1
- common_tyvars = exactTyVarsOfTypes [ty | (fld,ty) <- con1_flds `zip` con1_arg_tys
- , not (fld `elem` upd_field_lbls) ]
-
- is_common_tv tv = tv `elemVarSet` common_tyvars
-
- mk_inst_ty tv result_inst_ty
- | is_common_tv tv = returnM result_inst_ty -- Same as result type
- | otherwise = newFlexiTyVarTy (tyVarKind tv) -- Fresh type, of correct kind
- in
- tcInstTyVars con1_tyvars `thenM` \ (_, result_inst_tys, inst_env) ->
- zipWithM mk_inst_ty con1_tyvars result_inst_tys `thenM` \ inst_tys ->
-
- -- STEP 3
- -- Typecheck the update bindings.
- -- (Do this after checking for bad fields in case there's a field that
- -- doesn't match the constructor.)
- let
- result_record_ty = mkTyConApp tycon result_inst_tys
- con1_arg_tys' = map (substTy inst_env) con1_arg_tys
- in
- tcSubExp result_record_ty res_ty `thenM` \ co_fn ->
- tcRecordBinds con1 con1_arg_tys' rbinds `thenM` \ rbinds' ->
+ -- Other ones will cause a runtime error if they occur
+
+ -- Take apart a representative constructor
+ con1 = ASSERT( not (null relevant_cons) ) head relevant_cons
+ (con1_tvs, _, _, _, _, con1_arg_tys, _) = dataConFullSig con1
+ con1_flds = dataConFieldLabels con1
+ con1_res_ty = mkFamilyTyConApp tycon (mkTyVarTys con1_tvs)
+
+ -- Step 2
+ -- Check that at least one constructor has all the named fields
+ -- i.e. has an empty set of bad fields returned by badFields
+ ; checkTc (not (null relevant_cons)) (badFieldsUpd rbinds)
+
+ -- STEP 3 Note [Criteria for update]
+ -- Check that each updated field is polymorphic; that is, its type
+ -- mentions only the universally-quantified variables of the data con
+ ; let flds1_w_tys = zipEqual "tcExpr:RecConUpd" con1_flds con1_arg_tys
+ (upd_flds1_w_tys, fixed_flds1_w_tys) = partition is_updated flds1_w_tys
+ is_updated (fld,ty) = fld `elem` upd_fld_names
+
+ bad_upd_flds = filter bad_fld upd_flds1_w_tys
+ con1_tv_set = mkVarSet con1_tvs
+ bad_fld (fld, ty) = fld `elem` upd_fld_names &&
+ not (tyVarsOfType ty `subVarSet` con1_tv_set)
+ ; checkTc (null bad_upd_flds) (badFieldTypes bad_upd_flds)
+
+ -- STEP 4 Note [Type of a record update]
+ -- Figure out types for the scrutinee and result
+ -- Both are of form (T a b c), with fresh type variables, but with
+ -- common variables where the scrutinee and result must have the same type
+ -- These are variables that appear in *any* arg of *any* of the
+ -- relevant constructors *except* in the updated fields
+ --
+ ; let fixed_tvs = getFixedTyVars con1_tvs relevant_cons
+ is_fixed_tv tv = tv `elemVarSet` fixed_tvs
+ mk_inst_ty tv result_inst_ty
+ | is_fixed_tv tv = return result_inst_ty -- Same as result type
+ | otherwise = newFlexiTyVarTy (tyVarKind tv) -- Fresh type, of correct kind
+
+ ; (_, result_inst_tys, result_inst_env) <- tcInstTyVars con1_tvs
+ ; scrut_inst_tys <- zipWithM mk_inst_ty con1_tvs result_inst_tys
+
+ ; let result_ty = substTy result_inst_env con1_res_ty
+ con1_arg_tys' = map (substTy result_inst_env) con1_arg_tys
+ scrut_subst = zipTopTvSubst con1_tvs scrut_inst_tys
+ scrut_ty = substTy scrut_subst con1_res_ty
-- STEP 5
- -- Typecheck the expression to be updated
- let
- record_ty = ASSERT( length inst_tys == tyConArity tycon )
- mkTyConApp tycon inst_tys
- -- This is one place where the isVanilla check is important
- -- So that inst_tys matches the tycon
- in
- tcMonoExpr record_expr record_ty `thenM` \ record_expr' ->
-
- -- STEP 6
- -- Figure out the LIE we need. We have to generate some
- -- dictionaries for the data type context, since we are going to
- -- do pattern matching over the data cons.
- --
- -- What dictionaries do we need?
- -- We just take the context of the first data constructor
- -- This isn't right, but I just can't bear to union up all the relevant ones
- let
- theta' = substTheta inst_env (tyConStupidTheta tycon)
- in
- newDicts RecordUpdOrigin theta' `thenM` \ dicts ->
- extendLIEs dicts `thenM_`
+ -- Typecheck the thing to be updated, and the bindings
+ ; record_expr' <- tcMonoExpr record_expr scrut_ty
+ ; rbinds' <- tcRecordBinds con1 con1_arg_tys' rbinds
+
+ ; let origin = RecordUpdOrigin
+ ; co_fn <- tcSubExp origin result_ty res_ty
+
+ -- STEP 6: Deal with the stupid theta
+ ; let theta' = substTheta scrut_subst (dataConStupidTheta con1)
+ ; instStupidTheta origin theta'
+
+ -- Step 7: make a cast for the scrutinee, in the case that it's from a type family
+ ; let scrut_co | Just co_con <- tyConFamilyCoercion_maybe tycon
+ = WpCast $ mkTyConApp co_con scrut_inst_tys
+ | otherwise
+ = idHsWrapper
-- Phew!
- returnM (mkHsCoerce co_fn (RecordUpd record_expr' rbinds' record_ty result_record_ty))
+ ; return (mkHsWrap co_fn (RecordUpd (mkLHsWrap scrut_co record_expr') rbinds'
+ relevant_cons scrut_inst_tys result_inst_tys)) }
+ where
+ upd_fld_names = hsRecFields rbinds
+
+ getFixedTyVars :: [TyVar] -> [DataCon] -> TyVarSet
+ -- These tyvars must not change across the updates
+ getFixedTyVars tvs1 cons
+ = mkVarSet [tv1 | con <- cons
+ , let (tvs, theta, arg_tys, _) = dataConSig con
+ flds = dataConFieldLabels con
+ fixed_tvs = exactTyVarsOfTypes fixed_tys
+ -- fixed_tys: See Note [Type of a record update]
+ `unionVarSet` tyVarsOfTheta theta
+ -- Universally-quantified tyvars that
+ -- appear in any of the *implicit*
+ -- arguments to the constructor are fixed
+ -- See Note [Implict type sharing]
+
+ fixed_tys = [ty | (fld,ty) <- zip flds arg_tys
+ , not (fld `elem` upd_fld_names)]
+ , (tv1,tv) <- tvs1 `zip` tvs -- Discards existentials in tvs
+ , tv `elemVarSet` fixed_tvs ]
\end{code}
-
%************************************************************************
%* *
Arithmetic sequences e.g. [a,b..]
\begin{code}
tcExpr (ArithSeq _ seq@(From expr)) res_ty
- = do { elt_ty <- boxySplitListTy res_ty
+ = do { (elt_ty, coi) <- boxySplitListTy res_ty
; expr' <- tcPolyExpr expr elt_ty
; enum_from <- newMethodFromName (ArithSeqOrigin seq)
elt_ty enumFromName
- ; return (ArithSeq (HsVar enum_from) (From expr')) }
+ ; return $ mkHsWrapCoI coi (ArithSeq (HsVar enum_from) (From expr')) }
tcExpr in_expr@(ArithSeq _ seq@(FromThen expr1 expr2)) res_ty
- = do { elt_ty <- boxySplitListTy res_ty
+ = do { (elt_ty, coi) <- boxySplitListTy res_ty
; expr1' <- tcPolyExpr expr1 elt_ty
; expr2' <- tcPolyExpr expr2 elt_ty
; enum_from_then <- newMethodFromName (ArithSeqOrigin seq)
elt_ty enumFromThenName
- ; return (ArithSeq (HsVar enum_from_then) (FromThen expr1' expr2')) }
-
+ ; return $ mkHsWrapCoI coi
+ (ArithSeq (HsVar enum_from_then) (FromThen expr1' expr2')) }
tcExpr in_expr@(ArithSeq _ seq@(FromTo expr1 expr2)) res_ty
- = do { elt_ty <- boxySplitListTy res_ty
+ = do { (elt_ty, coi) <- boxySplitListTy res_ty
; expr1' <- tcPolyExpr expr1 elt_ty
; expr2' <- tcPolyExpr expr2 elt_ty
; enum_from_to <- newMethodFromName (ArithSeqOrigin seq)
elt_ty enumFromToName
- ; return (ArithSeq (HsVar enum_from_to) (FromTo expr1' expr2')) }
+ ; return $ mkHsWrapCoI coi
+ (ArithSeq (HsVar enum_from_to) (FromTo expr1' expr2')) }
tcExpr in_expr@(ArithSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
- = do { elt_ty <- boxySplitListTy res_ty
+ = do { (elt_ty, coi) <- boxySplitListTy res_ty
; expr1' <- tcPolyExpr expr1 elt_ty
; expr2' <- tcPolyExpr expr2 elt_ty
; expr3' <- tcPolyExpr expr3 elt_ty
; eft <- newMethodFromName (ArithSeqOrigin seq)
elt_ty enumFromThenToName
- ; return (ArithSeq (HsVar eft) (FromThenTo expr1' expr2' expr3')) }
+ ; return $ mkHsWrapCoI coi
+ (ArithSeq (HsVar eft) (FromThenTo expr1' expr2' expr3')) }
tcExpr in_expr@(PArrSeq _ seq@(FromTo expr1 expr2)) res_ty
- = do { [elt_ty] <- boxySplitTyConApp parrTyCon res_ty
+ = do { (elt_ty, coi) <- boxySplitPArrTy res_ty
; expr1' <- tcPolyExpr expr1 elt_ty
; expr2' <- tcPolyExpr expr2 elt_ty
; enum_from_to <- newMethodFromName (PArrSeqOrigin seq)
elt_ty enumFromToPName
- ; return (PArrSeq (HsVar enum_from_to) (FromTo expr1' expr2')) }
+ ; return $ mkHsWrapCoI coi
+ (PArrSeq (HsVar enum_from_to) (FromTo expr1' expr2')) }
tcExpr in_expr@(PArrSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
- = do { [elt_ty] <- boxySplitTyConApp parrTyCon res_ty
+ = do { (elt_ty, coi) <- boxySplitPArrTy res_ty
; expr1' <- tcPolyExpr expr1 elt_ty
; expr2' <- tcPolyExpr expr2 elt_ty
; expr3' <- tcPolyExpr expr3 elt_ty
; eft <- newMethodFromName (PArrSeqOrigin seq)
elt_ty enumFromThenToPName
- ; return (PArrSeq (HsVar eft) (FromThenTo expr1' expr2' expr3')) }
+ ; return $ mkHsWrapCoI coi
+ (PArrSeq (HsVar eft) (FromThenTo expr1' expr2' expr3')) }
tcExpr (PArrSeq _ _) _
= panic "TcExpr.tcMonoExpr: Infinite parallel array!"
tcExpr (HsSpliceE splice) res_ty = tcSpliceExpr splice res_ty
tcExpr (HsBracket brack) res_ty = do { e <- tcBracket brack res_ty
; return (unLoc e) }
+tcExpr e@(HsQuasiQuoteE _) res_ty =
+ pprPanic "Should never see HsQuasiQuoteE in type checker" (ppr e)
#endif /* GHCI */
\end{code}
---------------------------
tcApp :: HsExpr Name -- Function
-> Arity -- Number of args reqd
- -> ([BoxySigmaType] -> TcM arg_results) -- Argument type-checker
+ -> ArgChecker results
-> BoxyRhoType -- Result type
- -> TcM (HsExpr TcId, arg_results)
+ -> TcM (HsExpr TcId, results)
-- (tcFun fun n_args arg_checker res_ty)
-- The argument type checker, arg_checker, will be passed exactly n_args types
= tcIdApp fun_name n_args arg_checker res_ty
tcApp fun n_args arg_checker res_ty -- The vanilla case (rula APP)
- = do { arg_boxes <- newBoxyTyVars (replicate n_args argTypeKind)
- ; fun' <- tcExpr fun (mkFunTys (mkTyVarTys arg_boxes) res_ty)
- ; arg_tys' <- mapM readFilledBox arg_boxes
- ; args' <- arg_checker arg_tys'
+ = do { arg_boxes <- newBoxyTyVars (replicate n_args argTypeKind)
+ ; fun' <- tcExpr fun (mkFunTys (mkTyVarTys arg_boxes) res_ty)
+ ; arg_tys' <- mapM readFilledBox arg_boxes
+ ; (_, args') <- arg_checker [] [] arg_tys' -- Yuk
; return (fun', args') }
---------------------------
tcIdApp :: Name -- Function
-> Arity -- Number of args reqd
- -> ([BoxySigmaType] -> TcM arg_results) -- Argument type-checker
- -- The arg-checker guarantees to fill all boxes in the arg types
+ -> ArgChecker results -- The arg-checker guarantees to fill all boxes in the arg types
-> BoxyRhoType -- Result type
- -> TcM (HsExpr TcId, arg_results)
+ -> TcM (HsExpr TcId, results)
-- Call (f e1 ... en) :: res_ty
-- Type f :: forall a b c. theta => fa_1 -> ... -> fa_k -> fres
-- Then fres <= bx_(k+1) -> ... -> bx_n -> res_ty
tcIdApp fun_name n_args arg_checker res_ty
- = do { fun_id <- lookupFun (OccurrenceOf fun_name) fun_name
+ = do { let orig = OccurrenceOf fun_name
+ ; (fun, fun_ty) <- lookupFun orig fun_name
-- Split up the function type
- ; let (tv_theta_prs, rho) = tcMultiSplitSigmaTy (idType fun_id)
+ ; let (tv_theta_prs, rho) = tcMultiSplitSigmaTy fun_ty
(fun_arg_tys, fun_res_ty) = tcSplitFunTysN rho n_args
qtvs = concatMap fst tv_theta_prs -- Quantified tyvars
; let extra_arg_tys' = mkTyVarTys extra_arg_boxes
res_ty' = mkFunTys extra_arg_tys' res_ty
; qtys' <- preSubType qtvs tau_qtvs fun_res_ty res_ty'
- ; let arg_subst = zipOpenTvSubst qtvs qtys'
- fun_arg_tys' = substTys arg_subst fun_arg_tys
-- Typecheck the arguments!
-- Doing so will fill arg_qtvs and extra_arg_tys'
- ; args' <- arg_checker (fun_arg_tys' ++ extra_arg_tys')
+ ; (qtys'', args') <- arg_checker qtvs qtys' (fun_arg_tys ++ extra_arg_tys')
-- Strip boxes from the qtvs that have been filled in by the arg checking
- -- AND any variables that are mentioned in neither arg nor result
- -- the latter are mentioned only in constraints; stripBoxyType will
- -- fill them with a monotype
- ; let strip qtv qty' | qtv `elemVarSet` arg_qtvs = stripBoxyType qty'
- | otherwise = return qty'
- ; qtys'' <- zipWithM strip qtvs qtys'
; extra_arg_tys'' <- mapM readFilledBox extra_arg_boxes
-- Result subsumption
+ -- This fills in res_qtvs
; let res_subst = zipOpenTvSubst qtvs qtys''
fun_res_ty'' = substTy res_subst fun_res_ty
res_ty'' = mkFunTys extra_arg_tys'' res_ty
- ; co_fn <- tcFunResTy fun_name fun_res_ty'' res_ty''
+ ; co_fn <- tcSubExp orig fun_res_ty'' res_ty''
-- And pack up the results
-- By applying the coercion just to the *function* we can make
-- tcFun work nicely for OpApp and Sections too
- ; fun' <- instFun fun_id qtvs qtys'' tv_theta_prs
- ; co_fn' <- wrapFunResCoercion fun_arg_tys' co_fn
- ; return (mkHsCoerce co_fn' fun', args') }
+ ; fun' <- instFun orig fun res_subst tv_theta_prs
+ ; co_fn' <- wrapFunResCoercion (substTys res_subst fun_arg_tys) co_fn
+ ; traceTc (text "tcIdApp: " <+> ppr (mkHsWrap co_fn' fun') <+> ppr tv_theta_prs <+> ppr co_fn' <+> ppr fun')
+ ; return (mkHsWrap co_fn' fun', args') }
\end{code}
Note [Silly type synonyms in smart-app]
-> BoxyRhoType -- Result type
-> TcM (HsExpr TcId)
tcId orig fun_name res_ty
- = do { traceTc (text "tcId" <+> ppr fun_name <+> ppr res_ty)
- ; fun_id <- lookupFun orig fun_name
-
+ = do { (fun, fun_ty) <- lookupFun orig fun_name
+ ; traceTc (text "tcId" <+> ppr fun_name <+> (ppr fun_ty $$ ppr res_ty))
+
-- Split up the function type
- ; let (tv_theta_prs, fun_tau) = tcMultiSplitSigmaTy (idType fun_id)
- qtvs = concatMap fst tv_theta_prs -- Quantified tyvars
+ ; let (tv_theta_prs, fun_tau) = tcMultiSplitSigmaTy fun_ty
+ qtvs = concatMap fst tv_theta_prs -- Quantified tyvars
tau_qtvs = exactTyVarsOfType fun_tau -- Mentioned in the tau part
; qtv_tys <- preSubType qtvs tau_qtvs fun_tau res_ty
; let res_subst = zipTopTvSubst qtvs qtv_tys
fun_tau' = substTy res_subst fun_tau
- ; co_fn <- tcFunResTy fun_name fun_tau' res_ty
+ ; traceTc (text "tcId2" <+> ppr fun_name <+> (ppr qtvs $$ ppr qtv_tys))
+
+ ; co_fn <- tcSubExp orig fun_tau' res_ty
-- And pack up the results
- ; fun' <- instFun fun_id qtvs qtv_tys tv_theta_prs
- ; return (mkHsCoerce co_fn fun') }
+ ; fun' <- instFun orig fun res_subst tv_theta_prs
+ ; traceTc (text "tcId yields" <+> ppr (mkHsWrap co_fn fun'))
+ ; return (mkHsWrap co_fn fun') }
-- Note [Push result type in]
--
tcSyntaxOp :: InstOrigin -> HsExpr Name -> TcType -> TcM (HsExpr TcId)
-- Typecheck a syntax operator, checking that it has the specified type
-- The operator is always a variable at this stage (i.e. renamer output)
+-- This version assumes ty is a monotype
tcSyntaxOp orig (HsVar op) ty = tcId orig op ty
-tcSyntaxOp orig other ty = pprPanic "tcSyntaxOp" (ppr other)
-
+tcSyntaxOp orig other ty = pprPanic "tcSyntaxOp" (ppr other)
+
---------------------------
-instFun :: TcId
- -> [TyVar] -> [TcType] -- Quantified type variables and
- -- their instantiating types
- -> [([TyVar], ThetaType)] -- Stuff to instantiate
+instFun :: InstOrigin
+ -> HsExpr TcId
+ -> TvSubst -- The instantiating substitution
+ -> [([TyVar], ThetaType)] -- Stuff to instantiate
-> TcM (HsExpr TcId)
-instFun fun_id qtvs qtv_tys []
- = return (HsVar fun_id) -- Common short cut
-instFun fun_id qtvs qtv_tys tv_theta_prs
- = do { -- Horrid check for tagToEnum; see Note [tagToEnum#]
- checkBadTagToEnumCall fun_id qtv_tys
+instFun orig fun subst []
+ = return fun -- Common short cut
- ; let subst = zipOpenTvSubst qtvs qtv_tys
- ty_theta_prs' = map subst_pr tv_theta_prs
- subst_pr (tvs, theta) = (map (substTyVar subst) tvs,
- substTheta subst theta)
+instFun orig fun subst tv_theta_prs
+ = do { let ty_theta_prs' = map subst_pr tv_theta_prs
+ ; traceTc (text "instFun" <+> ppr ty_theta_prs')
+ -- Make two ad-hoc checks
+ ; doStupidChecks fun ty_theta_prs'
- -- The ty_theta_prs' is always non-empty
- ((tys1',theta1') : further_prs') = ty_theta_prs'
-
- -- First, chuck in the constraints from
- -- the "stupid theta" of a data constructor (sigh)
- ; case isDataConId_maybe fun_id of
- Just con -> tcInstStupidTheta con tys1'
- Nothing -> return ()
-
- ; if want_method_inst theta1'
- then do { meth_id <- newMethodWithGivenTy orig fun_id tys1'
- -- See Note [Multiple instantiation]
- ; go (HsVar meth_id) further_prs' }
- else go (HsVar fun_id) ty_theta_prs'
+ -- Now do normal instantiation
+ ; method_sharing <- doptM Opt_MethodSharing
+ ; result <- go method_sharing True fun ty_theta_prs'
+ ; traceTc (text "instFun result" <+> ppr result)
+ ; return result
}
where
- orig = OccurrenceOf (idName fun_id)
+ subst_pr (tvs, theta)
+ = (substTyVars subst tvs, substTheta subst theta)
- go fun [] = return fun
+ go _ _ fun [] = do {traceTc (text "go _ _ fun [] returns" <+> ppr fun) ; return fun }
- go fun ((tys, theta) : prs)
- = do { dicts <- newDicts orig theta
- ; extendLIEs dicts
- ; let the_app = unLoc $ mkHsDictApp (mkHsTyApp (noLoc fun) tys)
- (map instToId dicts)
- ; go the_app prs }
+ go method_sharing True (HsVar fun_id) ((tys,theta) : prs)
+ | want_method_inst method_sharing theta
+ = do { traceTc (text "go (HsVar fun_id) ((tys,theta) : prs) | want_method_inst theta")
+ ; meth_id <- newMethodWithGivenTy orig fun_id tys
+ ; go method_sharing False (HsVar meth_id) prs }
+ -- Go round with 'False' to prevent further use
+ -- of newMethod: see Note [Multiple instantiation]
+
+ go method_sharing _ fun ((tys, theta) : prs)
+ = do { co_fn <- instCall orig tys theta
+ ; traceTc (text "go yields co_fn" <+> ppr co_fn)
+ ; go method_sharing False (HsWrap co_fn fun) prs }
- -- Hack Alert (want_method_inst)!
-- See Note [No method sharing]
- -- If f :: (%x :: T) => Int -> Int
- -- Then if we have two separate calls, (f 3, f 4), we cannot
- -- make a method constraint that then gets shared, thus:
- -- let m = f %x in (m 3, m 4)
- -- because that loses the linearity of the constraint.
- -- The simplest thing to do is never to construct a method constraint
- -- in the first place that has a linear implicit parameter in it.
- want_method_inst theta = not (null theta) -- Overloaded
- && not (any isLinearPred theta) -- Not linear
- && not opt_NoMethodSharing
- -- See Note [No method sharing] below
+ want_method_inst method_sharing theta = not (null theta) -- Overloaded
+ && method_sharing
\end{code}
Note [Multiple instantiation]
a) it's better for RULEs involving overloaded functions
b) perhaps fewer separated lambdas
+Note [Left to right]
+~~~~~~~~~~~~~~~~~~~~
+tcArgs implements a left-to-right order, which goes beyond what is described in the
+impredicative type inference paper. In particular, it allows
+ runST $ foo
+where runST :: (forall s. ST s a) -> a
+When typechecking the application of ($)::(a->b) -> a -> b, we first check that
+runST has type (a->b), thereby filling in a=forall s. ST s a. Then we un-box this type
+before checking foo. The left-to-right order really helps here.
+
\begin{code}
tcArgs :: LHsExpr Name -- The function (for error messages)
- -> [LHsExpr Name] -> [TcSigmaType] -- Actual arguments and expected arg types
- -> TcM [LHsExpr TcId] -- Resulting args
+ -> [LHsExpr Name] -- Actual args
+ -> ArgChecker [LHsExpr TcId]
-tcArgs fun args expected_arg_tys
- = mapM (tcArg fun) (zip3 args expected_arg_tys [1..])
+type ArgChecker results
+ = [TyVar] -> [TcSigmaType] -- Current instantiation
+ -> [TcSigmaType] -- Expected arg types (**before** applying the instantiation)
+ -> TcM ([TcSigmaType], results) -- Resulting instantiation and args
-tcArg :: LHsExpr Name -- The function (for error messages)
- -> (LHsExpr Name, BoxySigmaType, Int) -- Actual argument and expected arg type
- -> TcM (LHsExpr TcId) -- Resulting argument
-tcArg fun (arg, ty, arg_no) = addErrCtxt (funAppCtxt fun arg arg_no) $
- tcPolyExprNC arg ty
+tcArgs fun args qtvs qtys arg_tys
+ = go 1 qtys args arg_tys
+ where
+ go n qtys [] [] = return (qtys, [])
+ go n qtys (arg:args) (arg_ty:arg_tys)
+ = do { arg' <- tcArg fun n arg qtvs qtys arg_ty
+ ; qtys' <- mapM refineBox qtys -- Exploit new info
+ ; (qtys'', args') <- go (n+1) qtys' args arg_tys
+ ; return (qtys'', arg':args') }
+ go n qtys args arg_tys = panic "tcArgs"
+
+tcArg :: LHsExpr Name -- The function
+ -> Int -- and arg number (for error messages)
+ -> LHsExpr Name
+ -> [TyVar] -> [TcSigmaType] -- Instantiate the arg type like this
+ -> BoxySigmaType
+ -> TcM (LHsExpr TcId) -- Resulting argument
+tcArg fun arg_no arg qtvs qtys ty
+ = addErrCtxt (funAppCtxt fun arg arg_no) $
+ tcPolyExprNC arg (substTyWith qtvs qtys ty)
\end{code}
\begin{code}
-checkBadTagToEnumCall :: Id -> [TcType] -> TcM ()
-checkBadTagToEnumCall fun_id tys
- | fun_id `hasKey` tagToEnumKey
+doStupidChecks :: HsExpr TcId
+ -> [([TcType], ThetaType)]
+ -> TcM ()
+-- Check two tiresome and ad-hoc cases
+-- (a) the "stupid theta" for a data con; add the constraints
+-- from the "stupid theta" of a data constructor (sigh)
+-- (b) deal with the tagToEnum# problem: see Note [tagToEnum#]
+
+doStupidChecks (HsVar fun_id) ((tys,_):_)
+ | Just con <- isDataConId_maybe fun_id -- (a)
+ = addDataConStupidTheta con tys
+
+ | fun_id `hasKey` tagToEnumKey -- (b)
= do { tys' <- zonkTcTypes tys
; checkTc (ok tys') (tagToEnumError tys')
}
- | otherwise -- Vastly common case
- = return ()
where
ok [] = False
ok (ty:tys) = case tcSplitTyConApp_maybe ty of
Just (tc,_) -> isEnumerationTyCon tc
Nothing -> False
+doStupidChecks fun tv_theta_prs
+ = return () -- The common case
+
+
tagToEnumError tys
- = hang (ptext SLIT("Bad call to tagToEnum#") <+> at_type)
- 2 (vcat [ptext SLIT("Specify the type by giving a type signature"),
- ptext SLIT("e.g. (tagToEnum# x) :: Bool")])
+ = hang (ptext (sLit "Bad call to tagToEnum#") <+> at_type)
+ 2 (vcat [ptext (sLit "Specify the type by giving a type signature"),
+ ptext (sLit "e.g. (tagToEnum# x) :: Bool")])
where
at_type | null tys = empty -- Probably never happens
- | otherwise = ptext SLIT("at type") <+> ppr (head tys)
+ | otherwise = ptext (sLit "at type") <+> ppr (head tys)
\end{code}
%************************************************************************
%* *
-\subsection{@tcId@ typchecks an identifier occurrence}
+\subsection{@tcId@ typechecks an identifier occurrence}
%* *
%************************************************************************
\begin{code}
-lookupFun :: InstOrigin -> Name -> TcM TcId
+lookupFun :: InstOrigin -> Name -> TcM (HsExpr TcId, TcType)
lookupFun orig id_name
= do { thing <- tcLookup id_name
; case thing of
- AGlobal (ADataCon con) -> return (dataConWrapId con)
+ AGlobal (ADataCon con) -> return (HsVar wrap_id, idType wrap_id)
+ where
+ wrap_id = dataConWrapId con
AGlobal (AnId id)
| isNaughtyRecordSelector id -> failWithTc (naughtyRecordSel id)
- | otherwise -> return id
+ | otherwise -> return (HsVar id, idType id)
-- A global cannot possibly be ill-staged
-- nor does it need the 'lifting' treatment
-#ifndef GHCI
- ATcId id th_level _ -> return id -- Non-TH case
-#else
- ATcId id th_level _ -> do { use_stage <- getStage -- TH case
- ; thLocalId orig id_name id th_level use_stage }
-#endif
-
- other -> failWithTc (ppr other <+> ptext SLIT("used where a value identifer was expected"))
+ ATcId { tct_id = id, tct_type = ty, tct_co = mb_co, tct_level = lvl }
+ | isNaughtyRecordSelector id -> failWithTc (naughtyRecordSel id)
+ -- Note [Local record selectors]
+ | otherwise
+ -> do { thLocalId orig id ty lvl
+ ; case mb_co of
+ Unrefineable -> return (HsVar id, ty)
+ Rigid co -> return (mkHsWrap co (HsVar id), ty)
+ Wobbly -> traceTc (text "lookupFun" <+> ppr id) >> return (HsVar id, ty) -- Wobbly, or no free vars
+ WobblyInvisible -> failWithTc (ppr id_name <+> ptext (sLit " not in scope because it has a wobbly type (solution: add a type annotation)"))
+ }
+
+ other -> failWithTc (ppr other <+> ptext (sLit "used where a value identifer was expected"))
}
-#ifdef GHCI /* GHCI and TH is on */
+#ifndef GHCI /* GHCI and TH is off */
--------------------------------------
--- thLocalId : Check for cross-stage lifting
-thLocalId orig id_name id th_bind_lvl (Brack use_lvl ps_var lie_var)
- | use_lvl > th_bind_lvl
- = thBrackId orig id_name id ps_var lie_var
-thLocalId orig id_name id th_bind_lvl use_stage
- = do { checkWellStaged (quotes (ppr id)) th_bind_lvl use_stage
- ; return id }
+thLocalId :: InstOrigin -> Id -> TcType -> ThLevel -> TcM ()
+-- Check for cross-stage lifting
+thLocalId orig id id_ty bind_lvl
+ = return ()
+
+#else /* GHCI and TH is on */
+thLocalId orig id id_ty bind_lvl
+ = do { use_stage <- getStage -- TH case
+ ; let use_lvl = thLevel use_stage
+ ; checkWellStaged (quotes (ppr id)) bind_lvl use_lvl
+ ; traceTc (text "thLocalId" <+> ppr id <+> ppr bind_lvl <+> ppr use_stage <+> ppr use_lvl)
+ ; when (use_lvl > bind_lvl) $
+ checkCrossStageLifting orig id id_ty bind_lvl use_stage }
--------------------------------------
-thBrackId orig id_name id ps_var lie_var
- | isExternalName id_name
+checkCrossStageLifting :: InstOrigin -> Id -> TcType -> ThLevel -> ThStage -> TcM ()
+-- We are inside brackets, and (use_lvl > bind_lvl)
+-- Now we must check whether there's a cross-stage lift to do
+-- Examples \x -> [| x |]
+-- [| map |]
+
+checkCrossStageLifting _ _ _ _ Comp = return ()
+checkCrossStageLifting _ _ _ _ Splice = return ()
+
+checkCrossStageLifting orig id id_ty bind_lvl (Brack _ ps_var lie_var)
+ | thTopLevelId id
= -- Top-level identifiers in this module,
-- (which have External Names)
-- are just like the imported case:
-- But we do need to put f into the keep-alive
-- set, because after desugaring the code will
-- only mention f's *name*, not f itself.
- do { keepAliveTc id_name; return id }
+ keepAliveTc id
- | otherwise
+ | otherwise -- bind_lvl = outerLevel presumably,
+ -- but the Id is not bound at top level
= -- Nested identifiers, such as 'x' in
-- E.g. \x -> [| h x |]
-- We must behave as if the reference to x was
-- If 'x' occurs many times we may get many identical
-- bindings of the same splice proxy, but that doesn't
-- matter, although it's a mite untidy.
- do { let id_ty = idType id
- ; checkTc (isTauTy id_ty) (polySpliceErr id)
+ do { checkTc (isTauTy id_ty) (polySpliceErr id)
-- If x is polymorphic, its occurrence sites might
-- have different instantiations, so we can't use plain
-- 'x' as the splice proxy name. I don't know how to
-- so we zap it to a LiftedTypeKind monotype
-- C.f. the call in TcPat.newLitInst
- ; setLIEVar lie_var $ do
- { lift <- newMethodFromName orig id_ty' DsMeta.liftName
- -- Put the 'lift' constraint into the right LIE
+ ; lift <- if isStringTy id_ty' then
+ tcLookupId DsMeta.liftStringName
+ -- See Note [Lifting strings]
+ else
+ setLIEVar lie_var $ do -- Put the 'lift' constraint into the right LIE
+ newMethodFromName orig id_ty' DsMeta.liftName
-- Update the pending splices
; ps <- readMutVar ps_var
- ; writeMutVar ps_var ((id_name, nlHsApp (nlHsVar lift) (nlHsVar id)) : ps)
+ ; writeMutVar ps_var ((idName id, nlHsApp (nlHsVar lift) (nlHsVar id)) : ps)
- ; return id } }
+ ; return () }
#endif /* GHCI */
\end{code}
+Note [Lifting strings]
+~~~~~~~~~~~~~~~~~~~~~~
+If we see $(... [| s |] ...) where s::String, we don't want to
+generate a mass of Cons (CharL 'x') (Cons (CharL 'y') ...)) etc.
+So this conditional short-circuits the lifting mechanism to generate
+(liftString "xy") in that case. I didn't want to use overlapping instances
+for the Lift class in TH.Syntax, because that can lead to overlapping-instance
+errors in a polymorphic situation.
+
+If this check fails (which isn't impossible) we get another chance; see
+Note [Converting strings] in Convert.lhs
+
+Local record selectors
+~~~~~~~~~~~~~~~~~~~~~~
+Record selectors for TyCons in this module are ordinary local bindings,
+which show up as ATcIds rather than AGlobals. So we need to check for
+naughtiness in both branches. c.f. TcTyClsBindings.mkAuxBinds.
+
%************************************************************************
%* *
-> HsRecordBinds Name
-> TcM (HsRecordBinds TcId)
-tcRecordBinds data_con arg_tys rbinds
- = do { mb_binds <- mappM do_bind rbinds
- ; return (catMaybes mb_binds) }
+tcRecordBinds data_con arg_tys (HsRecFields rbinds dd)
+ = do { mb_binds <- mapM do_bind rbinds
+ ; return (HsRecFields (catMaybes mb_binds) dd) }
where
flds_w_tys = zipEqual "tcRecordBinds" (dataConFieldLabels data_con) arg_tys
- do_bind (L loc field_lbl, rhs)
+ do_bind fld@(HsRecField { hsRecFieldId = L loc field_lbl, hsRecFieldArg = rhs })
| Just field_ty <- assocMaybe flds_w_tys field_lbl
= addErrCtxt (fieldCtxt field_lbl) $
- do { rhs' <- tcPolyExprNC rhs field_ty
- ; sel_id <- tcLookupId field_lbl
- ; ASSERT( isRecordSelector sel_id )
- return (Just (L loc sel_id, rhs')) }
+ do { rhs' <- tcPolyExprNC rhs field_ty
+ ; let field_id = mkUserLocal (nameOccName field_lbl)
+ (nameUnique field_lbl)
+ field_ty loc
+ -- Yuk: the field_id has the *unique* of the selector Id
+ -- (so we can find it easily)
+ -- but is a LocalId with the appropriate type of the RHS
+ -- (so the desugarer knows the type of local binder to make)
+ ; return (Just (fld { hsRecFieldId = L loc field_id, hsRecFieldArg = rhs' })) }
| otherwise
= do { addErrTc (badFieldCon data_con field_lbl)
; return Nothing }
checkMissingFields data_con rbinds
| null field_labels -- Not declared as a record;
-- But C{} is still valid if no strict fields
- = if any isMarkedStrict field_strs then
+ = if any isBanged field_strs then
-- Illegal if any arg is strict
addErrTc (missingStrictFields data_con [])
else
- returnM ()
+ return ()
- | otherwise -- A record
- = checkM (null missing_s_fields)
- (addErrTc (missingStrictFields data_con missing_s_fields)) `thenM_`
+ | otherwise = do -- A record
+ unless (null missing_s_fields)
+ (addErrTc (missingStrictFields data_con missing_s_fields))
- doptM Opt_WarnMissingFields `thenM` \ warn ->
- checkM (not (warn && notNull missing_ns_fields))
+ warn <- doptM Opt_WarnMissingFields
+ unless (not (warn && notNull missing_ns_fields))
(warnTc True (missingFields data_con missing_ns_fields))
where
missing_s_fields
= [ fl | (fl, str) <- field_info,
- isMarkedStrict str,
+ isBanged str,
not (fl `elem` field_names_used)
]
missing_ns_fields
= [ fl | (fl, str) <- field_info,
- not (isMarkedStrict str),
+ not (isBanged str),
not (fl `elem` field_names_used)
]
- field_names_used = recBindFields rbinds
+ field_names_used = hsRecFields rbinds
field_labels = dataConFieldLabels data_con
field_info = zipEqual "missingFields"
Boring and alphabetical:
\begin{code}
-caseScrutCtxt expr
- = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
+addExprErrCtxt :: OutputableBndr id => LHsExpr id -> TcM a -> TcM a
+addExprErrCtxt expr = addErrCtxt (exprCtxt (unLoc expr))
exprCtxt expr
- = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
+ = hang (ptext (sLit "In the expression:")) 4 (ppr expr)
fieldCtxt field_name
- = ptext SLIT("In the") <+> quotes (ppr field_name) <+> ptext SLIT("field of a record")
+ = ptext (sLit "In the") <+> quotes (ppr field_name) <+> ptext (sLit "field of a record")
funAppCtxt fun arg arg_no
- = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
+ = hang (hsep [ ptext (sLit "In the"), speakNth arg_no, ptext (sLit "argument of"),
quotes (ppr fun) <> text ", namely"])
4 (quotes (ppr arg))
-predCtxt expr
- = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
+badFieldTypes prs
+ = hang (ptext (sLit "Record update for insufficiently polymorphic field")
+ <> plural prs <> colon)
+ 2 (vcat [ ppr f <+> dcolon <+> ppr ty | (f,ty) <- prs ])
-nonVanillaUpd tycon
- = vcat [ptext SLIT("Record update for the non-Haskell-98 data type") <+> quotes (ppr tycon)
- <+> ptext SLIT("is not (yet) supported"),
- ptext SLIT("Use pattern-matching instead")]
badFieldsUpd rbinds
- = hang (ptext SLIT("No constructor has all these fields:"))
- 4 (pprQuotedList (recBindFields rbinds))
+ = hang (ptext (sLit "No constructor has all these fields:"))
+ 4 (pprQuotedList (hsRecFields rbinds))
naughtyRecordSel sel_id
- = ptext SLIT("Cannot use record selector") <+> quotes (ppr sel_id) <+>
- ptext SLIT("as a function due to escaped type variables") $$
- ptext SLIT("Probably fix: use pattern-matching syntax instead")
+ = ptext (sLit "Cannot use record selector") <+> quotes (ppr sel_id) <+>
+ ptext (sLit "as a function due to escaped type variables") $$
+ ptext (sLit "Probable fix: use pattern-matching syntax instead")
notSelector field
- = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
+ = hsep [quotes (ppr field), ptext (sLit "is not a record selector")]
missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
missingStrictFields con fields
-- with strict fields
| otherwise = colon <+> pprWithCommas ppr fields
- header = ptext SLIT("Constructor") <+> quotes (ppr con) <+>
- ptext SLIT("does not have the required strict field(s)")
+ header = ptext (sLit "Constructor") <+> quotes (ppr con) <+>
+ ptext (sLit "does not have the required strict field(s)")
missingFields :: DataCon -> [FieldLabel] -> SDoc
missingFields con fields
- = ptext SLIT("Fields of") <+> quotes (ppr con) <+> ptext SLIT("not initialised:")
+ = ptext (sLit "Fields of") <+> quotes (ppr con) <+> ptext (sLit "not initialised:")
<+> pprWithCommas ppr fields
-callCtxt fun args
- = ptext SLIT("In the call") <+> parens (ppr (foldl mkHsApp fun args))
+-- callCtxt fun args = ptext (sLit "In the call") <+> parens (ppr (foldl mkHsApp fun args))
#ifdef GHCI
polySpliceErr :: Id -> SDoc
polySpliceErr id
- = ptext SLIT("Can't splice the polymorphic local variable") <+> quotes (ppr id)
+ = ptext (sLit "Can't splice the polymorphic local variable") <+> quotes (ppr id)
#endif
\end{code}
projects / ghc-hetmet.git / blobdiff