X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2Ftypecheck%2FTcExpr.lhs;h=44964cffc80d925d3c346ab21a448c27ca5bdc24;hb=c29022c49449b7d8862dcc2259e16cafe9461945;hp=9f911d4b0064fb24adbca57c986ae2531efb8395;hpb=0596517a9b4b2b32e5d375a986351102ac4540fc;p=ghc-hetmet.git diff --git a/ghc/compiler/typecheck/TcExpr.lhs b/ghc/compiler/typecheck/TcExpr.lhs index 9f911d4..44964cf 100644 --- a/ghc/compiler/typecheck/TcExpr.lhs +++ b/ghc/compiler/typecheck/TcExpr.lhs @@ -4,64 +4,86 @@ \section[TcExpr]{Typecheck an expression} \begin{code} -#include "HsVersions.h" - -module TcExpr ( tcExpr ) where +module TcExpr ( tcExpr, tcStmt, tcId ) where -import Ubiq +#include "HsVersions.h" -import HsSyn ( HsExpr(..), Qual(..), Stmt(..), - HsBinds(..), Bind(..), MonoBinds(..), - ArithSeqInfo(..), HsLit(..), Sig, GRHSsAndBinds, - Match, Fake, InPat, OutPat, PolyType, - irrefutablePat, collectPatBinders ) -import RnHsSyn ( RenamedHsExpr(..), RenamedQual(..), RenamedStmt(..) ) -import TcHsSyn ( TcExpr(..), TcQual(..), TcStmt(..), TcIdOcc(..) ) +import HsSyn ( HsExpr(..), HsLit(..), ArithSeqInfo(..), + HsBinds(..), Stmt(..), DoOrListComp(..), + failureFreePat, collectPatBinders + ) +import RnHsSyn ( RenamedHsExpr, + RenamedStmt, RenamedRecordBinds + ) +import TcHsSyn ( TcExpr, TcStmt, + TcRecordBinds, + mkHsTyApp + ) import TcMonad +import BasicTypes ( RecFlag(..) ) + import Inst ( Inst, InstOrigin(..), OverloadedLit(..), - LIE(..), emptyLIE, plusLIE, newOverloadedLit, + LIE, emptyLIE, plusLIE, plusLIEs, newOverloadedLit, newMethod, newMethodWithGivenTy, newDicts ) -import TcBinds ( tcBindsAndThen ) -import TcEnv ( tcLookupLocalValue, tcLookupGlobalValue, tcLookupClassByKey, - tcLookupGlobalValueByKey, newMonoIds, tcGetGlobalTyVars ) -import TcMatches ( tcMatchesCase, tcMatch ) -import TcMonoType ( tcPolyType ) +import TcBinds ( tcBindsAndThen, checkSigTyVars, sigThetaCtxt ) +import TcEnv ( TcIdOcc(..), tcInstId, + tcLookupLocalValue, tcLookupGlobalValue, tcLookupClassByKey, + tcLookupGlobalValueByKey, newMonoIds, + tcExtendGlobalTyVars, tcLookupGlobalValueMaybe, + tcLookupTyCon + ) +import TcMatches ( tcMatchesCase, tcMatchExpected ) +import TcMonoType ( tcHsType ) import TcPat ( tcPat ) -import TcSimplify ( tcSimplifyAndCheck, tcSimplifyRank2 ) -import TcType ( TcType(..), TcMaybe(..), tcReadTyVar, - tcInstType, tcInstTcType, - tcInstTyVar, newTyVarTy, zonkTcTyVars ) +import TcSimplify ( tcSimplifyAndCheck ) +import TcType ( TcType, TcMaybe(..), + tcInstType, tcInstSigTcType, tcInstTyVars, + tcInstSigType, tcInstTcType, tcInstTheta, tcSplitRhoTy, + newTyVarTy, newTyVarTys, zonkTcType ) import TcKind ( TcKind ) -import Class ( Class(..), getClassSig ) -import Id ( Id(..), GenId, idType ) -import Kind ( Kind, mkBoxedTypeKind, mkTypeKind ) -import GenSpecEtc ( checkSigTyVars, checkSigTyVarsGivenGlobals, specTy ) -import PrelInfo ( intPrimTy, charPrimTy, doublePrimTy, - floatPrimTy, addrPrimTy, addrTy, - boolTy, charTy, stringTy, mkListTy, - mkTupleTy, mkPrimIoTy ) +import Class ( Class ) +import FieldLabel ( FieldLabel, fieldLabelName, fieldLabelType ) +import Id ( idType, dataConFieldLabels, dataConSig, recordSelectorFieldLabel, + isRecordSelector, + Id, GenId + ) +import Kind ( Kind, mkBoxedTypeKind, mkTypeKind, mkArrowKind ) +import Name ( Name{-instance Eq-} ) import Type ( mkFunTy, mkAppTy, mkTyVarTy, mkTyVarTys, - getTyVar_maybe, getFunTy_maybe, - splitForAllTy, splitRhoTy, splitSigmaTy, - isTauTy, mkFunTys, tyVarsOfType, getForAllTy_maybe ) -import TyVar ( GenTyVar, TyVarSet(..), unionTyVarSets, mkTyVarSet ) -import Unify ( unifyTauTy, unifyTauTyList, unifyTauTyLists ) + splitFunTy_maybe, splitFunTys, + mkTyConApp, + splitForAllTys, splitRhoTy, splitSigmaTy, + isTauTy, tyVarsOfType, tyVarsOfTypes, + splitForAllTy_maybe, splitAlgTyConApp, splitAlgTyConApp_maybe + ) +import TyVar ( emptyTyVarEnv, zipTyVarEnv, + elementOfTyVarSet, mkTyVarSet, tyVarSetToList + ) +import TyCon ( tyConDataCons ) +import TysPrim ( intPrimTy, charPrimTy, doublePrimTy, + floatPrimTy, addrPrimTy + ) +import TysWiredIn ( boolTy, charTy, stringTy ) +import PrelInfo ( ioTyCon_NAME ) +import Unify ( unifyTauTy, unifyFunTy, unifyListTy, unifyTupleTy ) import Unique ( Unique, cCallableClassKey, cReturnableClassKey, enumFromClassOpKey, enumFromThenClassOpKey, enumFromToClassOpKey, enumFromThenToClassOpKey, - monadClassKey, monadZeroClassKey ) - -import Name ( Name ) -- Instance + thenMClassOpKey, zeroClassOpKey, returnMClassOpKey + ) +import Outputable import PprType ( GenType, GenTyVar ) -- Instances import Maybes ( maybeToBool ) -import Pretty +import ListSetOps ( minusList ) import Util \end{code} \begin{code} -tcExpr :: RenamedHsExpr -> TcM s (TcExpr s, LIE s, TcType s) +tcExpr :: RenamedHsExpr -- Expession to type check + -> TcType s -- Expected type (could be a type variable) + -> TcM s (TcExpr s, LIE s) \end{code} %************************************************************************ @@ -71,16 +93,17 @@ tcExpr :: RenamedHsExpr -> TcM s (TcExpr s, LIE s, TcType s) %************************************************************************ \begin{code} -tcExpr (HsVar name) - = tcId name `thenTc` \ (expr', lie, res_ty) -> +tcExpr (HsVar name) res_ty + = tcId name `thenNF_Tc` \ (expr', lie, id_ty) -> + unifyTauTy res_ty id_ty `thenTc_` -- Check that the result type doesn't have any nested for-alls. -- For example, a "build" on its own is no good; it must be -- applied to something. - checkTc (isTauTy res_ty) - (lurkingRank2Err name res_ty) `thenTc_` + checkTc (isTauTy id_ty) + (lurkingRank2Err name id_ty) `thenTc_` - returnTc (expr', lie, res_ty) + returnTc (expr', lie) \end{code} %************************************************************************ @@ -92,59 +115,60 @@ tcExpr (HsVar name) Overloaded literals. \begin{code} -tcExpr (HsLit (HsInt i)) - = newTyVarTy mkBoxedTypeKind `thenNF_Tc` \ ty -> - - newOverloadedLit (LiteralOrigin (HsInt i)) +tcExpr (HsLit (HsInt i)) res_ty + = newOverloadedLit (LiteralOrigin (HsInt i)) (OverloadedIntegral i) - ty `thenNF_Tc` \ (lie, over_lit_id) -> - - returnTc (HsVar over_lit_id, lie, ty) - -tcExpr (HsLit (HsFrac f)) - = newTyVarTy mkBoxedTypeKind `thenNF_Tc` \ ty -> + res_ty `thenNF_Tc` \ stuff -> + returnTc stuff - newOverloadedLit (LiteralOrigin (HsFrac f)) +tcExpr (HsLit (HsFrac f)) res_ty + = newOverloadedLit (LiteralOrigin (HsFrac f)) (OverloadedFractional f) - ty `thenNF_Tc` \ (lie, over_lit_id) -> + res_ty `thenNF_Tc` \ stuff -> + returnTc stuff - returnTc (HsVar over_lit_id, lie, ty) -tcExpr (HsLit lit@(HsLitLit s)) +tcExpr (HsLit lit@(HsLitLit s)) res_ty = tcLookupClassByKey cCallableClassKey `thenNF_Tc` \ cCallableClass -> - newTyVarTy mkBoxedTypeKind `thenNF_Tc` \ ty -> newDicts (LitLitOrigin (_UNPK_ s)) - [(cCallableClass, ty)] `thenNF_Tc` \ (dicts, _) -> - returnTc (HsLitOut lit ty, dicts, ty) + [(cCallableClass, [res_ty])] `thenNF_Tc` \ (dicts, _) -> + returnTc (HsLitOut lit res_ty, dicts) \end{code} Primitive literals: \begin{code} -tcExpr (HsLit lit@(HsCharPrim c)) - = returnTc (HsLitOut lit charPrimTy, emptyLIE, charPrimTy) +tcExpr (HsLit lit@(HsCharPrim c)) res_ty + = unifyTauTy charPrimTy res_ty `thenTc_` + returnTc (HsLitOut lit charPrimTy, emptyLIE) -tcExpr (HsLit lit@(HsStringPrim s)) - = returnTc (HsLitOut lit addrPrimTy, emptyLIE, addrPrimTy) +tcExpr (HsLit lit@(HsStringPrim s)) res_ty + = unifyTauTy addrPrimTy res_ty `thenTc_` + returnTc (HsLitOut lit addrPrimTy, emptyLIE) -tcExpr (HsLit lit@(HsIntPrim i)) - = returnTc (HsLitOut lit intPrimTy, emptyLIE, intPrimTy) +tcExpr (HsLit lit@(HsIntPrim i)) res_ty + = unifyTauTy intPrimTy res_ty `thenTc_` + returnTc (HsLitOut lit intPrimTy, emptyLIE) -tcExpr (HsLit lit@(HsFloatPrim f)) - = returnTc (HsLitOut lit floatPrimTy, emptyLIE, floatPrimTy) +tcExpr (HsLit lit@(HsFloatPrim f)) res_ty + = unifyTauTy floatPrimTy res_ty `thenTc_` + returnTc (HsLitOut lit floatPrimTy, emptyLIE) -tcExpr (HsLit lit@(HsDoublePrim d)) - = returnTc (HsLitOut lit doublePrimTy, emptyLIE, doublePrimTy) +tcExpr (HsLit lit@(HsDoublePrim d)) res_ty + = unifyTauTy doublePrimTy res_ty `thenTc_` + returnTc (HsLitOut lit doublePrimTy, emptyLIE) \end{code} Unoverloaded literals: \begin{code} -tcExpr (HsLit lit@(HsChar c)) - = returnTc (HsLitOut lit charTy, emptyLIE, charTy) +tcExpr (HsLit lit@(HsChar c)) res_ty + = unifyTauTy charTy res_ty `thenTc_` + returnTc (HsLitOut lit charTy, emptyLIE) -tcExpr (HsLit lit@(HsString str)) - = returnTc (HsLitOut lit stringTy, emptyLIE, stringTy) +tcExpr (HsLit lit@(HsString str)) res_ty + = unifyTauTy stringTy res_ty `thenTc_` + returnTc (HsLitOut lit stringTy, emptyLIE) \end{code} %************************************************************************ @@ -154,21 +178,34 @@ tcExpr (HsLit lit@(HsString str)) %************************************************************************ \begin{code} -tcExpr (HsLam match) - = tcMatch match `thenTc` \ (match',lie,ty) -> - returnTc (HsLam match', lie, ty) +tcExpr (HsPar expr) res_ty -- preserve parens so printing needn't guess where they go + = tcExpr expr res_ty -tcExpr (HsApp e1 e2) = accum e1 [e2] +-- perform the negate *before* overloading the integer, since the case +-- of minBound on Ints fails otherwise. Could be done elsewhere, but +-- convenient to do it here. + +tcExpr (NegApp (HsLit (HsInt i)) neg) res_ty + = tcExpr (HsLit (HsInt (-i))) res_ty + +tcExpr (NegApp expr neg) res_ty + = tcExpr (HsApp neg expr) res_ty + +tcExpr (HsLam match) res_ty + = tcMatchExpected [] res_ty match `thenTc` \ (match',lie) -> + returnTc (HsLam match', lie) + +tcExpr (HsApp e1 e2) res_ty = accum e1 [e2] where accum (HsApp e1 e2) args = accum e1 (e2:args) accum fun args - = tcApp fun args `thenTc` \ (fun', args', lie, res_ty) -> - returnTc (foldl HsApp fun' args', lie, res_ty) + = tcApp fun args res_ty `thenTc` \ (fun', args', lie) -> + returnTc (foldl HsApp fun' args', lie) -- equivalent to (op e1) e2: -tcExpr (OpApp arg1 op arg2) - = tcApp op [arg1,arg2] `thenTc` \ (op', [arg1', arg2'], lie, res_ty) -> - returnTc (OpApp arg1' op' arg2', lie, res_ty) +tcExpr (OpApp arg1 op fix arg2) res_ty + = tcApp op [arg1,arg2] res_ty `thenTc` \ (op', [arg1', arg2'], lie) -> + returnTc (OpApp arg1' op' fix arg2', lie) \end{code} Note that the operators in sections are expected to be binary, and @@ -182,8 +219,8 @@ a type error will occur if they aren't. -- or just -- op e -tcExpr in_expr@(SectionL arg op) - = tcApp op [arg] `thenTc` \ (op', [arg'], lie, res_ty) -> +tcExpr in_expr@(SectionL arg op) res_ty + = tcApp op [arg] res_ty `thenTc` \ (op', [arg'], lie) -> -- Check that res_ty is a function type -- Without this check we barf in the desugarer on @@ -191,26 +228,21 @@ tcExpr in_expr@(SectionL arg op) -- because it tries to desugar to -- f op = \r -> 3 op r -- so (3 `op`) had better be a function! - newTyVarTy mkTypeKind `thenNF_Tc` \ ty1 -> - newTyVarTy mkTypeKind `thenNF_Tc` \ ty2 -> tcAddErrCtxt (sectionLAppCtxt in_expr) $ - unifyTauTy (mkFunTy ty1 ty2) res_ty `thenTc_` + unifyFunTy res_ty `thenTc_` - returnTc (SectionL arg' op', lie, res_ty) + returnTc (SectionL arg' op', lie) -- Right sections, equivalent to \ x -> x op expr, or -- \ x -> op x expr -tcExpr in_expr@(SectionR op expr) - = tcExpr op `thenTc` \ (op', lie1, op_ty) -> - tcExpr expr `thenTc` \ (expr',lie2, expr_ty) -> - - newTyVarTy mkTypeKind `thenNF_Tc` \ ty1 -> - newTyVarTy mkTypeKind `thenNF_Tc` \ ty2 -> +tcExpr in_expr@(SectionR op expr) res_ty + = tcExpr_id op `thenTc` \ (op', lie1, op_ty) -> tcAddErrCtxt (sectionRAppCtxt in_expr) $ - unifyTauTy op_ty (mkFunTys [ty1, expr_ty] ty2) `thenTc_` - - returnTc (SectionR op' expr', lie1 `plusLIE` lie2, mkFunTy ty1 ty2) + split_fun_ty op_ty 2 {- two args -} `thenTc` \ ([arg1_ty, arg2_ty], op_res_ty) -> + tcExpr expr arg2_ty `thenTc` \ (expr',lie2) -> + unifyTauTy (mkFunTy arg1_ty op_res_ty) res_ty `thenTc_` + returnTc (SectionR op' expr', lie1 `plusLIE` lie2) \end{code} The interesting thing about @ccall@ is that it is just a template @@ -221,195 +253,301 @@ arg/result types); unify them with the args/result; and store them for later use. \begin{code} -tcExpr (CCall lbl args may_gc is_asm ignored_fake_result_ty) +tcExpr (CCall lbl args may_gc is_asm ignored_fake_result_ty) res_ty = -- Get the callable and returnable classes. tcLookupClassByKey cCallableClassKey `thenNF_Tc` \ cCallableClass -> tcLookupClassByKey cReturnableClassKey `thenNF_Tc` \ cReturnableClass -> + tcLookupTyCon ioTyCon_NAME `thenTc` \ (_,_,ioTyCon) -> let new_arg_dict (arg, arg_ty) = newDicts (CCallOrigin (_UNPK_ lbl) (Just arg)) - [(cCallableClass, arg_ty)] `thenNF_Tc` \ (arg_dicts, _) -> + [(cCallableClass, [arg_ty])] `thenNF_Tc` \ (arg_dicts, _) -> returnNF_Tc arg_dicts -- Actually a singleton bag result_origin = CCallOrigin (_UNPK_ lbl) Nothing {- Not an arg -} in -- Arguments - tcExprs args `thenTc` \ (args', args_lie, arg_tys) -> + mapNF_Tc (\ _ -> newTyVarTy mkTypeKind) [1..(length args)] `thenNF_Tc` \ ty_vars -> + tcExprs args ty_vars `thenTc` \ (args', args_lie) -> -- The argument types can be unboxed or boxed; the result - -- type must, however, be boxed since it's an argument to the PrimIO + -- type must, however, be boxed since it's an argument to the IO -- type constructor. newTyVarTy mkBoxedTypeKind `thenNF_Tc` \ result_ty -> + let + io_result_ty = mkTyConApp ioTyCon [result_ty] + in + case tyConDataCons ioTyCon of { [ioDataCon] -> + unifyTauTy io_result_ty res_ty `thenTc_` -- Construct the extra insts, which encode the -- constraints on the argument and result types. - mapNF_Tc new_arg_dict (args `zip` arg_tys) `thenNF_Tc` \ ccarg_dicts_s -> - newDicts result_origin [(cReturnableClass, result_ty)] `thenNF_Tc` \ (ccres_dict, _) -> - - returnTc (CCall lbl args' may_gc is_asm result_ty, - foldr plusLIE ccres_dict ccarg_dicts_s `plusLIE` args_lie, - mkPrimIoTy result_ty) + mapNF_Tc new_arg_dict (zipEqual "tcExpr:CCall" args ty_vars) `thenNF_Tc` \ ccarg_dicts_s -> + newDicts result_origin [(cReturnableClass, [result_ty])] `thenNF_Tc` \ (ccres_dict, _) -> + + returnTc (HsApp (HsVar (RealId ioDataCon) `TyApp` [result_ty]) + (CCall lbl args' may_gc is_asm io_result_ty), + -- do the wrapping in the newtype constructor here + foldr plusLIE ccres_dict ccarg_dicts_s `plusLIE` args_lie) + } \end{code} \begin{code} -tcExpr (HsSCC label expr) - = tcExpr expr `thenTc` \ (expr', lie, expr_ty) -> - -- No unification. Give SCC the type of expr - returnTc (HsSCC label expr', lie, expr_ty) +tcExpr (HsSCC label expr) res_ty + = tcExpr expr res_ty `thenTc` \ (expr', lie) -> + returnTc (HsSCC label expr', lie) -tcExpr (HsLet binds expr) +tcExpr (HsLet binds expr) res_ty = tcBindsAndThen - HsLet -- The combiner + combiner binds -- Bindings to check - (tcExpr expr) -- Typechecker for the expression - -tcExpr in_expr@(HsCase expr matches src_loc) - = tcAddSrcLoc src_loc $ - tcExpr expr `thenTc` \ (expr',lie1,expr_ty) -> - newTyVarTy mkTypeKind `thenNF_Tc` \ result_ty -> + (tc_expr) `thenTc` \ (expr', lie) -> + returnTc (expr', lie) + where + tc_expr = tcExpr expr res_ty `thenTc` \ (expr', lie) -> + returnTc (expr', lie) + combiner is_rec bind expr = HsLet (MonoBind bind [] is_rec) expr - tcAddErrCtxt (caseCtxt in_expr) $ - tcMatchesCase (mkFunTy expr_ty result_ty) matches - `thenTc` \ (matches',lie2) -> +tcExpr in_expr@(HsCase scrut matches src_loc) res_ty + = tcAddSrcLoc src_loc $ + tcAddErrCtxt (caseCtxt in_expr) $ - returnTc (HsCase expr' matches' src_loc, plusLIE lie1 lie2, result_ty) + -- Typecheck the case alternatives first. + -- The case patterns tend to give good type info to use + -- when typechecking the scrutinee. For example + -- case (map f) of + -- (x:xs) -> ... + -- will report that map is applied to too few arguments -tcExpr (HsIf pred b1 b2 src_loc) - = tcAddSrcLoc src_loc $ - tcExpr pred `thenTc` \ (pred',lie1,predTy) -> + tcMatchesCase res_ty matches `thenTc` \ (scrut_ty, matches', lie2) -> - tcAddErrCtxt (predCtxt pred) ( - unifyTauTy predTy boolTy - ) `thenTc_` + tcAddErrCtxt (caseScrutCtxt scrut) ( + tcExpr scrut scrut_ty + ) `thenTc` \ (scrut',lie1) -> - tcExpr b1 `thenTc` \ (b1',lie2,result_ty) -> - tcExpr b2 `thenTc` \ (b2',lie3,b2Ty) -> + returnTc (HsCase scrut' matches' src_loc, plusLIE lie1 lie2) - tcAddErrCtxt (branchCtxt b1 b2) $ - unifyTauTy result_ty b2Ty `thenTc_` +tcExpr (HsIf pred b1 b2 src_loc) res_ty + = tcAddSrcLoc src_loc $ + tcAddErrCtxt (predCtxt pred) ( + tcExpr pred boolTy ) `thenTc` \ (pred',lie1) -> - returnTc (HsIf pred' b1' b2' src_loc, plusLIE lie1 (plusLIE lie2 lie3), result_ty) + tcExpr b1 res_ty `thenTc` \ (b1',lie2) -> + tcExpr b2 res_ty `thenTc` \ (b2',lie3) -> + returnTc (HsIf pred' b1' b2' src_loc, plusLIE lie1 (plusLIE lie2 lie3)) +\end{code} -tcExpr (ListComp expr quals) - = tcListComp expr quals `thenTc` \ ((expr',quals'), lie, ty) -> - returnTc (ListComp expr' quals', lie, ty) +\begin{code} +tcExpr expr@(HsDo do_or_lc stmts src_loc) res_ty + = tcDoStmts do_or_lc stmts src_loc res_ty \end{code} \begin{code} -tcExpr (HsDo stmts src_loc) - = -- get the Monad and MonadZero classes - -- create type consisting of a fresh monad tyvar - tcAddSrcLoc src_loc $ - tcLookupClassByKey monadClassKey `thenNF_Tc` \ monadClass -> - tcLookupClassByKey monadZeroClassKey `thenNF_Tc` \ monadZeroClass -> +tcExpr in_expr@(ExplicitList exprs) res_ty -- Non-empty list + = unifyListTy res_ty `thenTc` \ elt_ty -> + mapAndUnzipTc (tc_elt elt_ty) exprs `thenTc` \ (exprs', lies) -> + returnTc (ExplicitListOut elt_ty exprs', plusLIEs lies) + where + tc_elt elt_ty expr + = tcAddErrCtxt (listCtxt expr) $ + tcExpr expr elt_ty + +tcExpr (ExplicitTuple exprs) res_ty + = unifyTupleTy (length exprs) res_ty `thenTc` \ arg_tys -> + mapAndUnzipTc (\ (expr, arg_ty) -> tcExpr expr arg_ty) + (exprs `zip` arg_tys) -- we know they're of equal length. + `thenTc` \ (exprs', lies) -> + returnTc (ExplicitTuple exprs', plusLIEs lies) + +tcExpr (RecordCon con_name _ rbinds) res_ty + = tcLookupGlobalValue con_name `thenNF_Tc` \ con_id -> + tcId con_name `thenNF_Tc` \ (con_expr, con_lie, con_tau) -> let - (tv,_,_) = getClassSig monadClass + (_, record_ty) = splitFunTys con_tau in - tcInstTyVar tv `thenNF_Tc` \ m_tyvar -> + -- Con is syntactically constrained to be a data constructor + ASSERT( maybeToBool (splitAlgTyConApp_maybe record_ty ) ) + unifyTauTy res_ty record_ty `thenTc_` + + -- Check that the record bindings match the constructor let - m = mkTyVarTy m_tyvar + bad_fields = badFields rbinds con_id in - tcDoStmts False m stmts `thenTc` \ ((stmts',monad,mzero), lie, do_ty) -> - - -- create dictionaries for monad and possibly monadzero - (if monad then - newDicts DoOrigin [(monadClass, m)] - else - returnNF_Tc (emptyLIE, [panic "TcExpr: MonadZero dictionary"]) - ) `thenNF_Tc` \ (m_lie, [m_id]) -> - (if mzero then - newDicts DoOrigin [(monadZeroClass, m)] - else - returnNF_Tc (emptyLIE, [panic "TcExpr: MonadZero dictionary"]) - ) `thenNF_Tc` \ (mz_lie, [mz_id]) -> - - returnTc (HsDoOut stmts' m_id mz_id src_loc, - lie `plusLIE` m_lie `plusLIE` mz_lie, - do_ty) -\end{code} + checkTc (null bad_fields) (badFieldsCon con_id bad_fields) `thenTc_` + + -- Typecheck the record bindings + -- (Do this after checkRecordFields in case there's a field that + -- doesn't match the constructor.) + tcRecordBinds record_ty rbinds `thenTc` \ (rbinds', rbinds_lie) -> + + returnTc (RecordCon (RealId con_id) con_expr rbinds', con_lie `plusLIE` rbinds_lie) + + +-- 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. + +tcExpr (RecordUpd record_expr rbinds) res_ty + = tcAddErrCtxt recordUpdCtxt $ + + -- STEP 1 + -- Figure out the tycon and data cons from the first field name + ASSERT( not (null rbinds) ) + let + ((first_field_name, _, _) : rest) = rbinds + in + tcLookupGlobalValueMaybe first_field_name `thenNF_Tc` \ maybe_sel_id -> + (case maybe_sel_id of + Just sel_id | isRecordSelector sel_id -> returnTc sel_id + other -> failWithTc (notSelector first_field_name) + ) `thenTc` \ sel_id -> + let + (_, tau) = splitForAllTys (idType sel_id) + Just (data_ty, _) = splitFunTy_maybe tau -- Must succeed since sel_id is a selector + (tycon, _, data_cons) = splitAlgTyConApp data_ty + (con_tyvars, theta, _, _, _, _) = dataConSig (head data_cons) + in + tcInstTyVars con_tyvars `thenNF_Tc` \ (_, result_inst_tys, _) -> + + -- STEP 2 + -- Check for bad fields + checkTc (any (null . badFields rbinds) data_cons) + (badFieldsUpd rbinds) `thenTc_` + -- 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 + in + unifyTauTy res_ty result_record_ty `thenTc_` + tcRecordBinds result_record_ty rbinds `thenTc` \ (rbinds', rbinds_lie) -> + + -- 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 + upd_field_lbls = [recordSelectorFieldLabel sel_id | (RealId sel_id, _, _) <- rbinds'] + con_field_lbls_s = map dataConFieldLabels data_cons -\begin{code} -tcExpr (ExplicitList []) - = newTyVarTy mkBoxedTypeKind `thenNF_Tc` \ tyvar_ty -> - returnTc (ExplicitListOut tyvar_ty [], emptyLIE, mkListTy tyvar_ty) + -- A constructor is only relevant to this process if + -- it contains all the fields that are being updated + relevant_field_lbls_s = filter is_relevant con_field_lbls_s + is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls + non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls + common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls) -tcExpr in_expr@(ExplicitList exprs) -- Non-empty list - = tcExprs exprs `thenTc` \ (exprs', lie, tys@(elt_ty:_)) -> - tcAddErrCtxt (listCtxt in_expr) $ - unifyTauTyList tys `thenTc_` - returnTc (ExplicitListOut elt_ty exprs', lie, mkListTy elt_ty) + mk_inst_ty (tyvar, result_inst_ty) + | tyvar `elementOfTyVarSet` common_tyvars = returnNF_Tc result_inst_ty -- Same as result type + | otherwise = newTyVarTy mkBoxedTypeKind -- Fresh type + in + mapNF_Tc mk_inst_ty (zip con_tyvars result_inst_tys) `thenNF_Tc` \ inst_tys -> -tcExpr (ExplicitTuple exprs) - = tcExprs exprs `thenTc` \ (exprs', lie, tys) -> - returnTc (ExplicitTuple exprs', lie, mkTupleTy (length tys) tys) + -- STEP 5 + -- Typecheck the expression to be updated + let + record_ty = mkTyConApp tycon inst_tys + in + tcExpr record_expr record_ty `thenTc` \ (record_expr', record_lie) -> + + -- 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 some construction. + -- + -- What dictionaries do we need? For the moment we assume that all + -- data constructors have the same context, and grab it from the first + -- constructor. If they have varying contexts then we'd have to + -- union the ones that could participate in the update. + let + (tyvars, theta, _, _, _, _) = dataConSig (head data_cons) + inst_env = zipTyVarEnv tyvars result_inst_tys + in + tcInstTheta inst_env theta `thenNF_Tc` \ theta' -> + newDicts RecordUpdOrigin theta' `thenNF_Tc` \ (con_lie, dicts) -> -tcExpr (RecordCon con rbinds) - = panic "tcExpr:RecordCon" -tcExpr (RecordUpd exp rbinds) - = panic "tcExpr:RecordUpd" + -- Phew! + returnTc (RecordUpdOut record_expr' result_record_ty dicts rbinds', + con_lie `plusLIE` record_lie `plusLIE` rbinds_lie) -tcExpr (ArithSeqIn seq@(From expr)) - = tcExpr expr `thenTc` \ (expr', lie1, ty) -> +tcExpr (ArithSeqIn seq@(From expr)) res_ty + = unifyListTy res_ty `thenTc` \ elt_ty -> + tcExpr expr elt_ty `thenTc` \ (expr', lie1) -> tcLookupGlobalValueByKey enumFromClassOpKey `thenNF_Tc` \ sel_id -> newMethod (ArithSeqOrigin seq) - (RealId sel_id) [ty] `thenNF_Tc` \ (lie2, enum_from_id) -> + (RealId sel_id) [elt_ty] `thenNF_Tc` \ (lie2, enum_from_id) -> returnTc (ArithSeqOut (HsVar enum_from_id) (From expr'), - lie1 `plusLIE` lie2, - mkListTy ty) - -tcExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) - = tcExpr expr1 `thenTc` \ (expr1',lie1,ty1) -> - tcExpr expr2 `thenTc` \ (expr2',lie2,ty2) -> - - tcAddErrCtxt (arithSeqCtxt in_expr) $ - unifyTauTyList [ty1, ty2] `thenTc_` + lie1 `plusLIE` lie2) +tcExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty + = tcAddErrCtxt (arithSeqCtxt in_expr) $ + unifyListTy res_ty `thenTc` \ elt_ty -> + tcExpr expr1 elt_ty `thenTc` \ (expr1',lie1) -> + tcExpr expr2 elt_ty `thenTc` \ (expr2',lie2) -> tcLookupGlobalValueByKey enumFromThenClassOpKey `thenNF_Tc` \ sel_id -> newMethod (ArithSeqOrigin seq) - (RealId sel_id) [ty1] `thenNF_Tc` \ (lie3, enum_from_then_id) -> + (RealId sel_id) [elt_ty] `thenNF_Tc` \ (lie3, enum_from_then_id) -> returnTc (ArithSeqOut (HsVar enum_from_then_id) (FromThen expr1' expr2'), - lie1 `plusLIE` lie2 `plusLIE` lie3, - mkListTy ty1) - -tcExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) - = tcExpr expr1 `thenTc` \ (expr1',lie1,ty1) -> - tcExpr expr2 `thenTc` \ (expr2',lie2,ty2) -> - - tcAddErrCtxt (arithSeqCtxt in_expr) $ - unifyTauTyList [ty1,ty2] `thenTc_` + lie1 `plusLIE` lie2 `plusLIE` lie3) +tcExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty + = tcAddErrCtxt (arithSeqCtxt in_expr) $ + unifyListTy res_ty `thenTc` \ elt_ty -> + tcExpr expr1 elt_ty `thenTc` \ (expr1',lie1) -> + tcExpr expr2 elt_ty `thenTc` \ (expr2',lie2) -> tcLookupGlobalValueByKey enumFromToClassOpKey `thenNF_Tc` \ sel_id -> newMethod (ArithSeqOrigin seq) - (RealId sel_id) [ty1] `thenNF_Tc` \ (lie3, enum_from_to_id) -> + (RealId sel_id) [elt_ty] `thenNF_Tc` \ (lie3, enum_from_to_id) -> returnTc (ArithSeqOut (HsVar enum_from_to_id) (FromTo expr1' expr2'), - lie1 `plusLIE` lie2 `plusLIE` lie3, - mkListTy ty1) - -tcExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) - = tcExpr expr1 `thenTc` \ (expr1',lie1,ty1) -> - tcExpr expr2 `thenTc` \ (expr2',lie2,ty2) -> - tcExpr expr3 `thenTc` \ (expr3',lie3,ty3) -> - - tcAddErrCtxt (arithSeqCtxt in_expr) $ - unifyTauTyList [ty1,ty2,ty3] `thenTc_` - + lie1 `plusLIE` lie2 `plusLIE` lie3) + +tcExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty + = tcAddErrCtxt (arithSeqCtxt in_expr) $ + unifyListTy res_ty `thenTc` \ elt_ty -> + tcExpr expr1 elt_ty `thenTc` \ (expr1',lie1) -> + tcExpr expr2 elt_ty `thenTc` \ (expr2',lie2) -> + tcExpr expr3 elt_ty `thenTc` \ (expr3',lie3) -> tcLookupGlobalValueByKey enumFromThenToClassOpKey `thenNF_Tc` \ sel_id -> newMethod (ArithSeqOrigin seq) - (RealId sel_id) [ty1] `thenNF_Tc` \ (lie4, eft_id) -> + (RealId sel_id) [elt_ty] `thenNF_Tc` \ (lie4, eft_id) -> returnTc (ArithSeqOut (HsVar eft_id) (FromThenTo expr1' expr2' expr3'), - lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` lie4, - mkListTy ty1) + lie1 `plusLIE` lie2 `plusLIE` lie3 `plusLIE` lie4) \end{code} %************************************************************************ @@ -419,29 +557,64 @@ tcExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) %************************************************************************ \begin{code} -tcExpr in_expr@(ExprWithTySig expr poly_ty) - = tcExpr expr `thenTc` \ (texpr, lie, tau_ty) -> - tcPolyType poly_ty `thenTc` \ sigma_sig -> +tcExpr in_expr@(ExprWithTySig expr poly_ty) res_ty + = tcSetErrCtxt (exprSigCtxt in_expr) $ + tcHsType poly_ty `thenTc` \ sigma_sig -> -- Check the tau-type part - tcSetErrCtxt (exprSigCtxt in_expr) $ - specTy SignatureOrigin sigma_sig `thenNF_Tc` \ (sig_tyvars, sig_dicts, sig_tau, _) -> - unifyTauTy tau_ty sig_tau `thenTc_` + tcInstSigType sigma_sig `thenNF_Tc` \ sigma_sig' -> + let + (sig_tyvars', sig_theta', sig_tau') = splitSigmaTy sigma_sig' + in + + -- Type check the expression, expecting the signature type + tcExtendGlobalTyVars sig_tyvars' ( + tcExpr expr sig_tau' + ) `thenTc` \ (texpr, lie) -> - -- Check the type variables of the signature - checkSigTyVars sig_tyvars sig_tau tau_ty `thenTc` \ sig_tyvars' -> + -- Check the type variables of the signature, + -- *after* typechecking the expression + checkSigTyVars sig_tyvars' sig_tau' `thenTc` \ zonked_sig_tyvars -> -- Check overloading constraints - tcSimplifyAndCheck - (mkTyVarSet sig_tyvars') - sig_dicts lie `thenTc_` + newDicts SignatureOrigin sig_theta' `thenNF_Tc` \ (sig_dicts, _) -> + tcAddErrCtxtM (sigThetaCtxt sig_dicts) ( + tcSimplifyAndCheck + (text "expr ty sig") + (mkTyVarSet zonked_sig_tyvars) + sig_dicts lie + ) `thenTc_` + + -- Now match the signature type with res_ty. + -- We must not do this earlier, because res_ty might well + -- mention variables free in the environment, and we'd get + -- bogus complaints about not being able to for-all the + -- sig_tyvars + unifyTauTy sig_tau' res_ty `thenTc_` -- If everything is ok, return the stuff unchanged, except for -- the effect of any substutions etc. We simply discard the -- result of the tcSimplifyAndCheck, except for any default -- resolution it may have done, which is recorded in the -- substitution. - returnTc (texpr, lie, tau_ty) + returnTc (texpr, lie) + +\end{code} + +Typecheck expression which in most cases will be an Id. + +\begin{code} +tcExpr_id :: RenamedHsExpr + -> TcM s (TcExpr s, + LIE s, + TcType s) +tcExpr_id id_expr + = case id_expr of + HsVar name -> tcId name `thenNF_Tc` \ stuff -> + returnTc stuff + other -> newTyVarTy mkTypeKind `thenNF_Tc` \ id_ty -> + tcExpr id_expr id_ty `thenTc` \ (id_expr', lie_id) -> + returnTc (id_expr', lie_id, id_ty) \end{code} %************************************************************************ @@ -451,93 +624,85 @@ tcExpr in_expr@(ExprWithTySig expr poly_ty) %************************************************************************ \begin{code} + tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args + -> TcType s -- Expected result type of application -> TcM s (TcExpr s, [TcExpr s], -- Translated fun and args - LIE s, - TcType s) -- Type of the application + LIE s) -tcApp fun args +tcApp fun args res_ty = -- First type-check the function - -- In the HsVar case we go straight to tcId to avoid hitting the - -- rank-2 check, which we check later here anyway - (case fun of - HsVar name -> tcId name - other -> tcExpr fun - ) `thenTc` \ (fun', lie_fun, fun_ty) -> - - tcApp_help fun 1 fun_ty args `thenTc` \ (args', lie_args, res_ty) -> - - -- Check that the result type doesn't have any nested for-alls. - -- For example, a "build" on its own is no good; it must be applied to something. - checkTc (isTauTy res_ty) - (lurkingRank2Err fun fun_ty) `thenTc_` - - returnTc (fun', args', lie_fun `plusLIE` lie_args, res_ty) + tcExpr_id fun `thenTc` \ (fun', lie_fun, fun_ty) -> + tcAddErrCtxt (wrongArgsCtxt "too many" fun args) ( + split_fun_ty fun_ty (length args) + ) `thenTc` \ (expected_arg_tys, actual_result_ty) -> -tcApp_help :: RenamedHsExpr -> Int -- Function and arg position, used in error message(s) - -> TcType s -- The type of the function - -> [RenamedHsExpr] -- Arguments - -> TcM s ([TcExpr s], -- Typechecked args - LIE s, - TcType s) -- Result type of the application + -- Unify with expected result before type-checking the args + -- This is when we might detect a too-few args situation + tcAddErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty) ( + unifyTauTy res_ty actual_result_ty + ) `thenTc_` -tcApp_help orig_fun arg_no fun_ty [] - = returnTc ([], emptyLIE, fun_ty) + -- Now typecheck the args + mapAndUnzipTc (tcArg fun) + (zip3 args expected_arg_tys [1..]) `thenTc` \ (args', lie_args_s) -> -tcApp_help orig_fun arg_no fun_ty (arg:args) - | maybeToBool maybe_arrow_ty - = -- The function's type is A->B - tcAddErrCtxt (funAppCtxt orig_fun arg_no arg) ( - tcArg expected_arg_ty arg - ) `thenTc` \ (arg', lie_arg) -> - - tcApp_help orig_fun (arg_no+1) result_ty args `thenTc` \ (args', lie_args, res_ty) -> - returnTc (arg':args', lie_arg `plusLIE` lie_args, res_ty) - - | maybeToBool maybe_tyvar_ty - = -- The function's type is just a type variable - tcReadTyVar fun_tyvar `thenNF_Tc` \ maybe_fun_ty -> - case maybe_fun_ty of + -- Check that the result type doesn't have any nested for-alls. + -- For example, a "build" on its own is no good; it must be applied to something. + checkTc (isTauTy actual_result_ty) + (lurkingRank2Err fun fun_ty) `thenTc_` - BoundTo new_fun_ty -> -- The tyvar in the corner of the function is bound - -- to something ... so carry on .... - tcApp_help orig_fun arg_no new_fun_ty (arg:args) + returnTc (fun', args', lie_fun `plusLIE` plusLIEs lie_args_s) - UnBound -> -- Extra args match against an unbound type - -- variable as the final result type, so unify the tyvar. - newTyVarTy mkTypeKind `thenNF_Tc` \ result_ty -> - tcExprs args `thenTc` \ (args', lie_args, arg_tys) -> - -- Unification can't fail, since we're unifying against a tyvar - unifyTauTy fun_ty (mkFunTys arg_tys result_ty) `thenTc_` +-- If an error happens we try to figure out whether the +-- function has been given too many or too few arguments, +-- and say so +checkArgsCtxt fun args expected_res_ty actual_res_ty + = zonkTcType expected_res_ty `thenNF_Tc` \ exp_ty' -> + zonkTcType actual_res_ty `thenNF_Tc` \ act_ty' -> + let + (exp_args, _) = splitFunTys exp_ty' + (act_args, _) = splitFunTys act_ty' + message | length exp_args < length act_args = wrongArgsCtxt "too few" fun args + | length exp_args > length act_args = wrongArgsCtxt "too many" fun args + | otherwise = appCtxt fun args + in + returnNF_Tc message - returnTc (args', lie_args, result_ty) - | otherwise - = -- Must be an error: a lurking for-all, or (more commonly) - -- a TyConTy... we've applied the function to too many args - failTc (tooManyArgs orig_fun) +split_fun_ty :: TcType s -- The type of the function + -> Int -- Number of arguments + -> TcM s ([TcType s], -- Function argument types + TcType s) -- Function result types - where - maybe_arrow_ty = getFunTy_maybe fun_ty - Just (expected_arg_ty, result_ty) = maybe_arrow_ty +split_fun_ty fun_ty 0 + = returnTc ([], fun_ty) - maybe_tyvar_ty = getTyVar_maybe fun_ty - Just fun_tyvar = maybe_tyvar_ty +split_fun_ty fun_ty n + = -- Expect the function to have type A->B + unifyFunTy fun_ty `thenTc` \ (arg_ty, res_ty) -> + split_fun_ty res_ty (n-1) `thenTc` \ (arg_tys, final_res_ty) -> + returnTc (arg_ty:arg_tys, final_res_ty) \end{code} \begin{code} -tcArg :: TcType s -- Expected arg type - -> RenamedHsExpr -- Actual argument +tcArg :: RenamedHsExpr -- The function (for error messages) + -> (RenamedHsExpr, TcType s, Int) -- Actual argument and expected arg type -> TcM s (TcExpr s, LIE s) -- Resulting argument and LIE -tcArg expected_arg_ty arg - | not (maybeToBool (getForAllTy_maybe expected_arg_ty)) +tcArg the_fun (arg, expected_arg_ty, arg_no) + = tcAddErrCtxt (funAppCtxt the_fun arg arg_no) $ + tcPolyExpr arg expected_arg_ty + + +-- tcPolyExpr is like tcExpr, except that the expected type +-- can be a polymorphic one. +tcPolyExpr arg expected_arg_ty + | not (maybeToBool (splitForAllTy_maybe expected_arg_ty)) = -- The ordinary, non-rank-2 polymorphic case - tcExpr arg `thenTc` \ (arg', lie_arg, actual_arg_ty) -> - unifyTauTy expected_arg_ty actual_arg_ty `thenTc_` - returnTc (arg', lie_arg) + tcExpr arg expected_arg_ty | otherwise = -- Ha! The argument type of the function is a for-all type, @@ -547,14 +712,16 @@ tcArg expected_arg_ty arg -- of instantiating a function involving rank-2 polymorphism, so there -- isn't any danger of using the same tyvars twice -- The argument type shouldn't be overloaded type (hence ASSERT) + + -- To ensure that the forall'd type variables don't get unified with each + -- other or any other types, we make fresh *signature* type variables + -- and unify them with the tyvars. + tcInstSigTcType expected_arg_ty `thenNF_Tc` \ (sig_tyvars, sig_rho) -> let - (expected_tyvars, expected_theta, expected_tau) = splitSigmaTy expected_arg_ty + (sig_theta, sig_tau) = splitRhoTy sig_rho in - ASSERT( null expected_theta ) - -- Type-check the arg and unify with expected type - tcExpr arg `thenTc` \ (arg', lie_arg, actual_arg_ty) -> - unifyTauTy expected_tau actual_arg_ty `thenTc_` ( + tcExpr arg sig_tau `thenTc` \ (arg', lie_arg) -> -- Check that the arg_tyvars havn't been constrained -- The interesting bit here is that we must include the free variables @@ -566,33 +733,28 @@ tcArg expected_arg_ty arg -- So now s' isn't unconstrained because it's linked to a. -- Conclusion: include the free vars of the expected arg type in the -- list of "free vars" for the signature check. - tcAddErrCtxt (rank2ArgCtxt arg expected_arg_ty) $ - tcGetGlobalTyVars `thenNF_Tc` \ env_tyvars -> - zonkTcTyVars (tyVarsOfType expected_arg_ty) `thenNF_Tc` \ free_tyvars -> - checkSigTyVarsGivenGlobals - (env_tyvars `unionTyVarSets` free_tyvars) - expected_tyvars expected_tau actual_arg_ty `thenTc` \ arg_tyvars' -> - - -- Check that there's no overloading involved - -- Even if there isn't, there may be some Insts which mention the arg_tyvars, - -- but which, on simplification, don't actually need a dictionary involving - -- the tyvar. So we have to do a proper simplification right here. - tcSimplifyRank2 (mkTyVarSet arg_tyvars') - lie_arg `thenTc` \ (free_insts, inst_binds) -> - - -- This HsLet binds any Insts which came out of the simplification. - -- It's a bit out of place here, but using AbsBind involves inventing - -- a couple of new names which seems worse. - returnTc (TyLam arg_tyvars' (HsLet (mk_binds inst_binds) arg'), free_insts) - ) - where - mk_binds [] - = EmptyBinds - mk_binds ((inst,rhs):inst_binds) - = (SingleBind (NonRecBind (VarMonoBind inst rhs))) - `ThenBinds` - mk_binds inst_binds + tcAddErrCtxt (rank2ArgCtxt arg expected_arg_ty) $ + tcExtendGlobalTyVars (tyVarSetToList (tyVarsOfType expected_arg_ty)) $ + + checkSigTyVars sig_tyvars sig_tau `thenTc` \ zonked_sig_tyvars -> + newDicts Rank2Origin sig_theta `thenNF_Tc` \ (sig_dicts, dict_ids) -> + -- ToDo: better origin + + tcAddErrCtxtM (sigThetaCtxt sig_dicts) $ + tcSimplifyAndCheck (text "rank2") + (mkTyVarSet zonked_sig_tyvars) + sig_dicts lie_arg `thenTc` \ (free_insts, inst_binds) -> + + -- This HsLet binds any Insts which came out of the simplification. + -- It's a bit out of place here, but using AbsBind involves inventing + -- a couple of new names which seems worse. + returnTc ( TyLam zonked_sig_tyvars $ + DictLam dict_ids $ + HsLet (MonoBind inst_binds [] Recursive) + arg' + , free_insts + ) \end{code} %************************************************************************ @@ -602,154 +764,250 @@ tcArg expected_arg_ty arg %************************************************************************ \begin{code} -tcId :: Name -> TcM s (TcExpr s, LIE s, TcType s) +tcId :: Name -> NF_TcM s (TcExpr s, LIE s, TcType s) + tcId name = -- Look up the Id and instantiate its type - (tcLookupLocalValue name `thenNF_Tc` \ maybe_local -> - case maybe_local of - Just tc_id -> tcInstTcType [] (idType tc_id) `thenNF_Tc` \ ty -> - returnNF_Tc (TcId tc_id, ty) - - Nothing -> tcLookupGlobalValue name `thenNF_Tc` \ id -> - tcInstType [] (idType id) `thenNF_Tc` \ ty -> - returnNF_Tc (RealId id, ty) - ) `thenNF_Tc` \ (tc_id_occ, ty) -> - let - (tyvars, rho) = splitForAllTy ty - (theta,tau) = splitRhoTy rho - arg_tys = mkTyVarTys tyvars - in - -- Is it overloaded? - case theta of - [] -> -- Not overloaded, so just make a type application - returnTc (TyApp (HsVar tc_id_occ) arg_tys, emptyLIE, tau) - - _ -> -- Overloaded, so make a Method inst - newMethodWithGivenTy (OccurrenceOf tc_id_occ) - tc_id_occ arg_tys rho `thenNF_Tc` \ (lie, meth_id) -> - returnTc (HsVar meth_id, lie, tau) -\end{code} + tcLookupLocalValue name `thenNF_Tc` \ maybe_local -> + case maybe_local of + Just tc_id -> instantiate_it (TcId tc_id) (idType tc_id) + Nothing -> tcLookupGlobalValue name `thenNF_Tc` \ id -> + tcInstType emptyTyVarEnv (idType id) `thenNF_Tc` \ inst_ty -> + let + (tyvars, rho) = splitForAllTys inst_ty + in + instantiate_it2 (RealId id) tyvars rho + + where + -- The instantiate_it loop runs round instantiating the Id. + -- It has to be a loop because we are now prepared to entertain + -- types like + -- f:: forall a. Eq a => forall b. Baz b => tau + -- We want to instantiate this to + -- f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)} + instantiate_it tc_id_occ ty + = tcInstTcType ty `thenNF_Tc` \ (tyvars, rho) -> + instantiate_it2 tc_id_occ tyvars rho + + instantiate_it2 tc_id_occ tyvars rho + = tcSplitRhoTy rho `thenNF_Tc` \ (theta, tau) -> + if null theta then -- Is it overloaded? + returnNF_Tc (mkHsTyApp (HsVar tc_id_occ) arg_tys, emptyLIE, tau) + else + -- Yes, it's overloaded + newMethodWithGivenTy (OccurrenceOf tc_id_occ) + tc_id_occ arg_tys theta tau `thenNF_Tc` \ (lie1, meth_id) -> + instantiate_it meth_id tau `thenNF_Tc` \ (expr, lie2, final_tau) -> + returnNF_Tc (expr, lie1 `plusLIE` lie2, final_tau) + + where + arg_tys = mkTyVarTys tyvars +\end{code} %************************************************************************ %* * -\subsection{@tcQuals@ typchecks list comprehension qualifiers} +\subsection{@tcDoStmts@ typechecks a {\em list} of do statements} %* * %************************************************************************ \begin{code} -tcListComp expr [] - = tcExpr expr `thenTc` \ (expr', lie, ty) -> - returnTc ((expr',[]), lie, mkListTy ty) - -tcListComp expr (qual@(FilterQual filter) : quals) - = tcAddErrCtxt (qualCtxt qual) ( - tcExpr filter `thenTc` \ (filter', filter_lie, filter_ty) -> - unifyTauTy boolTy filter_ty `thenTc_` - returnTc (FilterQual filter', filter_lie) - ) `thenTc` \ (qual', qual_lie) -> - - tcListComp expr quals `thenTc` \ ((expr',quals'), rest_lie, res_ty) -> - - returnTc ((expr', qual' : quals'), - qual_lie `plusLIE` rest_lie, - res_ty) - -tcListComp expr (qual@(GeneratorQual pat rhs) : quals) - = newMonoIds binder_names mkBoxedTypeKind (\ ids -> - - tcAddErrCtxt (qualCtxt qual) ( - tcPat pat `thenTc` \ (pat', lie_pat, pat_ty) -> - tcExpr rhs `thenTc` \ (rhs', lie_rhs, rhs_ty) -> - unifyTauTy (mkListTy pat_ty) rhs_ty `thenTc_` - returnTc (GeneratorQual pat' rhs', - lie_pat `plusLIE` lie_rhs) - ) `thenTc` \ (qual', lie_qual) -> - - tcListComp expr quals `thenTc` \ ((expr',quals'), lie_rest, res_ty) -> - - returnTc ((expr', qual' : quals'), - lie_qual `plusLIE` lie_rest, - res_ty) - ) - where - binder_names = collectPatBinders pat +tcDoStmts do_or_lc stmts src_loc res_ty + = -- get the Monad and MonadZero classes + -- create type consisting of a fresh monad tyvar + ASSERT( not (null stmts) ) + tcAddSrcLoc src_loc $ + newTyVarTy (mkArrowKind mkBoxedTypeKind mkBoxedTypeKind) `thenNF_Tc` \ m -> + + let + tc_stmts [] = returnTc (([], error "tc_stmts"), emptyLIE) + tc_stmts (stmt:stmts) = tcStmt tcExpr do_or_lc (mkAppTy m) combine_stmts stmt $ + tc_stmts stmts + + combine_stmts stmt@(ReturnStmt _) (Just ty) ([], _) = ([stmt], ty) + combine_stmts stmt@(ExprStmt e _) (Just ty) ([], _) = ([stmt], ty) + combine_stmts stmt _ ([], _) = panic "Bad last stmt tcDoStmts" + combine_stmts stmt _ (stmts, ty) = (stmt:stmts, ty) + in + tc_stmts stmts `thenTc` \ ((stmts', result_ty), final_lie) -> + unifyTauTy result_ty res_ty `thenTc_` + + -- Build the then and zero methods in case we need them + -- It's important that "then" and "return" appear just once in the final LIE, + -- not only for typechecker efficiency, but also because otherwise during + -- simplification we end up with silly stuff like + -- then = case d of (t,r) -> t + -- then = then + -- where the second "then" sees that it already exists in the "available" stuff. + -- + tcLookupGlobalValueByKey returnMClassOpKey `thenNF_Tc` \ return_sel_id -> + tcLookupGlobalValueByKey thenMClassOpKey `thenNF_Tc` \ then_sel_id -> + tcLookupGlobalValueByKey zeroClassOpKey `thenNF_Tc` \ zero_sel_id -> + newMethod DoOrigin + (RealId return_sel_id) [m] `thenNF_Tc` \ (return_lie, return_id) -> + newMethod DoOrigin + (RealId then_sel_id) [m] `thenNF_Tc` \ (then_lie, then_id) -> + newMethod DoOrigin + (RealId zero_sel_id) [m] `thenNF_Tc` \ (zero_lie, zero_id) -> + let + monad_lie = then_lie `plusLIE` return_lie `plusLIE` perhaps_zero_lie + perhaps_zero_lie | all failure_free stmts' = emptyLIE + | otherwise = zero_lie + + failure_free (BindStmt pat _ _) = failureFreePat pat + failure_free (GuardStmt _ _) = False + failure_free other_stmt = True + in + returnTc (HsDoOut do_or_lc stmts' return_id then_id zero_id res_ty src_loc, + final_lie `plusLIE` monad_lie) -tcListComp expr (LetQual binds : quals) - = tcBindsAndThen -- No error context, but a binding group is - combine -- rather a large thing for an error context anyway - binds - (tcListComp expr quals) - where - combine binds' (expr',quals') = (expr', LetQual binds' : quals') \end{code} +\begin{code} +tcStmt :: (RenamedHsExpr -> TcType s -> TcM s (TcExpr s, LIE s)) -- This is tcExpr + -- The sole, disgusting, reason for this parameter + -- is to get the effect of polymorphic recursion + -- ToDo: rm when booting with Haskell 1.3 + -> DoOrListComp + -> (TcType s -> TcType s) -- Relationship type of pat and rhs in pat <- rhs + -> (TcStmt s -> Maybe (TcType s) -> thing -> thing) + -> RenamedStmt + -> TcM s (thing, LIE s) + -> TcM s (thing, LIE s) + +tcStmt tc_expr do_or_lc m combine stmt@(ReturnStmt exp) do_next + = ASSERT( case do_or_lc of { DoStmt -> False; ListComp -> True; Guard -> True } ) + tcSetErrCtxt (stmtCtxt do_or_lc stmt) ( + newTyVarTy mkTypeKind `thenNF_Tc` \ exp_ty -> + tc_expr exp exp_ty `thenTc` \ (exp', exp_lie) -> + returnTc (ReturnStmt exp', exp_lie, m exp_ty) + ) `thenTc` \ (stmt', stmt_lie, stmt_ty) -> + do_next `thenTc` \ (thing', thing_lie) -> + returnTc (combine stmt' (Just stmt_ty) thing', + stmt_lie `plusLIE` thing_lie) + +tcStmt tc_expr do_or_lc m combine stmt@(GuardStmt exp src_loc) do_next + = ASSERT( case do_or_lc of { DoStmt -> False; ListComp -> True; Guard -> True } ) + newTyVarTy mkTypeKind `thenNF_Tc` \ exp_ty -> + tcAddSrcLoc src_loc ( + tcSetErrCtxt (stmtCtxt do_or_lc stmt) ( + tc_expr exp boolTy `thenTc` \ (exp', exp_lie) -> + returnTc (GuardStmt exp' src_loc, exp_lie) + )) `thenTc` \ (stmt', stmt_lie) -> + do_next `thenTc` \ (thing', thing_lie) -> + returnTc (combine stmt' Nothing thing', + stmt_lie `plusLIE` thing_lie) + +tcStmt tc_expr do_or_lc m combine stmt@(ExprStmt exp src_loc) do_next + = ASSERT( case do_or_lc of { DoStmt -> True; ListComp -> False; Guard -> False } ) + newTyVarTy mkTypeKind `thenNF_Tc` \ exp_ty -> + tcAddSrcLoc src_loc ( + tcSetErrCtxt (stmtCtxt do_or_lc stmt) ( + newTyVarTy mkTypeKind `thenNF_Tc` \ tau -> + let + -- exp has type (m tau) for some tau (doesn't matter what) + exp_ty = m tau + in + tc_expr exp exp_ty `thenTc` \ (exp', exp_lie) -> + returnTc (ExprStmt exp' src_loc, exp_lie, exp_ty) + )) `thenTc` \ (stmt', stmt_lie, stmt_ty) -> + do_next `thenTc` \ (thing', thing_lie) -> + returnTc (combine stmt' (Just stmt_ty) thing', + stmt_lie `plusLIE` thing_lie) + +tcStmt tc_expr do_or_lc m combine stmt@(BindStmt pat exp src_loc) do_next + = newMonoIds (collectPatBinders pat) mkBoxedTypeKind $ \ _ -> + tcAddSrcLoc src_loc ( + tcSetErrCtxt (stmtCtxt do_or_lc stmt) ( + tcPat pat `thenTc` \ (pat', pat_lie, pat_ty) -> + tc_expr exp (m pat_ty) `thenTc` \ (exp', exp_lie) -> + + -- NB: the environment has been extended with the new binders + -- which the rhs can't "see", but the renamer should have made + -- sure that everything is distinct by now, so there's no problem. + -- Putting the tcExpr before the newMonoIds messes up the nesting + -- of error contexts, so I didn't bother + + returnTc (BindStmt pat' exp' src_loc, pat_lie `plusLIE` exp_lie) + )) `thenTc` \ (stmt', stmt_lie) -> + do_next `thenTc` \ (thing', thing_lie) -> + returnTc (combine stmt' Nothing thing', + stmt_lie `plusLIE` thing_lie) + +tcStmt tc_expr do_or_lc m combine (LetStmt binds) do_next + = tcBindsAndThen -- No error context, but a binding group is + combine' -- rather a large thing for an error context anyway + binds + do_next + where + combine' is_rec binds' thing' = combine (LetStmt (MonoBind binds' [] is_rec)) Nothing thing' +\end{code} %************************************************************************ %* * -\subsection{@tcDoStmts@ typechecks a {\em list} of do statements} +\subsection{Record bindings} %* * %************************************************************************ -\begin{code} -tcDoStmts :: Bool -- True => require a monad - -> TcType s -- m - -> [RenamedStmt] - -> TcM s (([TcStmt s], - Bool, -- True => Monad - Bool), -- True => MonadZero - LIE s, - TcType s) - -tcDoStmts monad m [stmt@(ExprStmt exp src_loc)] - = tcAddSrcLoc src_loc $ - tcSetErrCtxt (stmtCtxt stmt) $ - tcExpr exp `thenTc` \ (exp', exp_lie, exp_ty) -> - (if monad then - newTyVarTy mkTypeKind `thenNF_Tc` \ a -> - unifyTauTy (mkAppTy m a) exp_ty - else - returnTc () - ) `thenTc_` - returnTc (([ExprStmt exp' src_loc], monad, False), exp_lie, exp_ty) - -tcDoStmts _ m (stmt@(ExprStmt exp src_loc) : stmts) - = tcAddSrcLoc src_loc ( - tcSetErrCtxt (stmtCtxt stmt) ( - tcExpr exp `thenTc` \ (exp', exp_lie, exp_ty) -> - newTyVarTy mkTypeKind `thenNF_Tc` \ a -> - unifyTauTy (mkAppTy m a) exp_ty `thenTc_` - returnTc (ExprStmt exp' src_loc, exp_lie) - )) `thenTc` \ (stmt', stmt_lie) -> - tcDoStmts True m stmts `thenTc` \ ((stmts', _, mzero), stmts_lie, stmts_ty) -> - returnTc ((stmt':stmts', True, mzero), - stmt_lie `plusLIE` stmts_lie, - stmts_ty) - -tcDoStmts _ m (stmt@(BindStmt pat exp src_loc) : stmts) - = tcAddSrcLoc src_loc ( - tcSetErrCtxt (stmtCtxt stmt) ( - tcPat pat `thenTc` \ (pat', pat_lie, pat_ty) -> - tcExpr exp `thenTc` \ (exp', exp_lie, exp_ty) -> - newTyVarTy mkTypeKind `thenNF_Tc` \ a -> - unifyTauTy a pat_ty `thenTc_` - unifyTauTy (mkAppTy m a) exp_ty `thenTc_` - returnTc (BindStmt pat' exp' src_loc, pat_lie `plusLIE` exp_lie, irrefutablePat pat') - )) `thenTc` \ (stmt', stmt_lie, failure_free) -> - tcDoStmts True m stmts `thenTc` \ ((stmts', _, mzero), stmts_lie, stmts_ty) -> - returnTc ((stmt':stmts', True, mzero || not failure_free), - stmt_lie `plusLIE` stmts_lie, - stmts_ty) - -tcDoStmts monad m (LetStmt binds : stmts) - = tcBindsAndThen -- No error context, but a binding group is - combine -- rather a large thing for an error context anyway - binds - (tcDoStmts monad m stmts) - where - combine binds' (stmts', monad, mzero) = ((LetStmt binds' : stmts'), monad, mzero) +Game plan for record bindings +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +For each binding + field = value +1. look up "field", to find its selector Id, which must have type + forall a1..an. T a1 .. an -> tau + where tau is the type of the field. + +2. Instantiate this type +3. Unify the (T a1 .. an) part with the "expected result type", which + is passed in. This checks that all the field labels come from the + same type. + +4. Type check the value using tcArg, passing tau as the expected + argument type. + +This extends OK when the field types are universally quantified. + +Actually, to save excessive creation of fresh type variables, +we + +\begin{code} +tcRecordBinds + :: TcType s -- Expected type of whole record + -> RenamedRecordBinds + -> TcM s (TcRecordBinds s, LIE s) + +tcRecordBinds expected_record_ty rbinds + = mapAndUnzipTc do_bind rbinds `thenTc` \ (rbinds', lies) -> + returnTc (rbinds', plusLIEs lies) + where + do_bind (field_label, rhs, pun_flag) + = tcLookupGlobalValue field_label `thenNF_Tc` \ sel_id -> + ASSERT( isRecordSelector sel_id ) + -- This lookup and assertion will surely succeed, because + -- we check that the fields are indeed record selectors + -- before calling tcRecordBinds + + tcInstId sel_id `thenNF_Tc` \ (_, _, tau) -> + + -- Record selectors all have type + -- forall a1..an. T a1 .. an -> tau + ASSERT( maybeToBool (splitFunTy_maybe tau) ) + let + -- Selector must have type RecordType -> FieldType + Just (record_ty, field_ty) = splitFunTy_maybe tau + in + unifyTauTy expected_record_ty record_ty `thenTc_` + tcPolyExpr rhs field_ty `thenTc` \ (rhs', lie) -> + returnTc ((RealId sel_id, rhs', pun_flag), lie) + +badFields rbinds data_con + = [field_name | (field_name, _, _) <- rbinds, + not (field_name `elem` field_names) + ] + where + field_names = map fieldLabelName (dataConFieldLabels data_con) \end{code} %************************************************************************ @@ -759,13 +1017,13 @@ tcDoStmts monad m (LetStmt binds : stmts) %************************************************************************ \begin{code} -tcExprs :: [RenamedHsExpr] -> TcM s ([TcExpr s], LIE s, [TcType s]) +tcExprs :: [RenamedHsExpr] -> [TcType s] -> TcM s ([TcExpr s], LIE s) -tcExprs [] = returnTc ([], emptyLIE, []) -tcExprs (expr:exprs) - = tcExpr expr `thenTc` \ (expr', lie1, ty) -> - tcExprs exprs `thenTc` \ (exprs', lie2, tys) -> - returnTc (expr':exprs', lie1 `plusLIE` lie2, ty:tys) +tcExprs [] [] = returnTc ([], emptyLIE) +tcExprs (expr:exprs) (ty:tys) + = tcExpr expr ty `thenTc` \ (expr', lie1) -> + tcExprs exprs tys `thenTc` \ (exprs', lie2) -> + returnTc (expr':exprs', lie1 `plusLIE` lie2) \end{code} @@ -776,63 +1034,84 @@ Errors and contexts Mini-utils: \begin{code} -pp_nest_hang :: String -> Pretty -> Pretty -pp_nest_hang label stuff = ppNest 2 (ppHang (ppStr label) 4 stuff) +pp_nest_hang :: String -> SDoc -> SDoc +pp_nest_hang label stuff = nest 2 (hang (text label) 4 stuff) \end{code} Boring and alphabetical: \begin{code} -arithSeqCtxt expr sty - = ppHang (ppStr "In an arithmetic sequence:") 4 (ppr sty expr) +arithSeqCtxt expr + = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr) + +caseCtxt expr + = hang (ptext SLIT("In the case expression:")) 4 (ppr expr) -branchCtxt b1 b2 sty - = ppSep [ppStr "In the branches of a conditional:", - pp_nest_hang "`then' branch:" (ppr sty b1), - pp_nest_hang "`else' branch:" (ppr sty b2)] +caseScrutCtxt expr + = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr) -caseCtxt expr sty - = ppHang (ppStr "In a case expression:") 4 (ppr sty expr) +exprSigCtxt expr + = hang (ptext SLIT("In an expression with a type signature:")) + 4 (ppr expr) -exprSigCtxt expr sty - = ppHang (ppStr "In an expression with a type signature:") - 4 (ppr sty expr) +listCtxt expr + = hang (ptext SLIT("In the list element:")) 4 (ppr expr) -listCtxt expr sty - = ppHang (ppStr "In a list expression:") 4 (ppr sty expr) +predCtxt expr + = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr) -predCtxt expr sty - = ppHang (ppStr "In a predicate expression:") 4 (ppr sty expr) +sectionRAppCtxt expr + = hang (ptext SLIT("In the right section:")) 4 (ppr expr) -sectionRAppCtxt expr sty - = ppHang (ppStr "In a right section:") 4 (ppr sty expr) +sectionLAppCtxt expr + = hang (ptext SLIT("In the left section:")) 4 (ppr expr) -sectionLAppCtxt expr sty - = ppHang (ppStr "In a left section:") 4 (ppr sty expr) +funAppCtxt fun arg arg_no + = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"), + quotes (ppr fun) <> text ", namely"]) + 4 (quotes (ppr arg)) -funAppCtxt fun arg_no arg sty - = ppHang (ppCat [ ppStr "In the", speakNth arg_no, ppStr "argument of", ppr sty fun]) - 4 (ppCat [ppStr "namely", ppr sty arg]) +stmtCtxt do_or_lc stmt + = hang (ptext SLIT("In a") <+> whatever <> colon) + 4 (ppr stmt) + where + whatever = case do_or_lc of + ListComp -> ptext SLIT("list-comprehension qualifier") + DoStmt -> ptext SLIT("do statement") + Guard -> ptext SLIT("guard") + +wrongArgsCtxt too_many_or_few fun args + = hang (ptext SLIT("Probable cause:") <+> ppr fun + <+> ptext SLIT("is applied to") <+> text too_many_or_few + <+> ptext SLIT("arguments in the call")) + 4 (ppr the_app) + where + the_app = foldl HsApp fun args -- Used in error messages -qualCtxt qual sty - = ppHang (ppStr "In a list-comprehension qualifer:") - 4 (ppr sty qual) +appCtxt fun args + = ptext SLIT("In the application") <+> (ppr the_app) + where + the_app = foldl HsApp fun args -- Used in error messages -stmtCtxt stmt sty - = ppHang (ppStr "In a do statement:") - 4 (ppr sty stmt) +lurkingRank2Err fun fun_ty + = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)]) + 4 (vcat [ptext SLIT("It is applied to too few arguments"), + ptext SLIT("so that the result type has for-alls in it")]) -tooManyArgs f sty - = ppHang (ppStr "Too many arguments in an application of the function") - 4 (ppr sty f) +rank2ArgCtxt arg expected_arg_ty + = ptext SLIT("In a polymorphic function argument:") <+> ppr arg -lurkingRank2Err fun fun_ty sty - = ppHang (ppCat [ppStr "Illegal use of", ppr sty fun]) - 4 (ppAboves [ppStr "It is applied to too few arguments,", - ppStr "so that the result type has for-alls in it"]) +badFieldsUpd rbinds + = hang (ptext SLIT("No constructor has all these fields:")) + 4 (pprQuotedList fields) + where + fields = [field | (field, _, _) <- rbinds] -rank2ArgCtxt arg expected_arg_ty sty - = ppHang (ppStr "In a polymorphic function argument:") - 4 (ppSep [ppBeside (ppr sty arg) (ppStr " ::"), - ppr sty expected_arg_ty]) -\end{code} +recordUpdCtxt = ptext SLIT("In a record update construct") + +badFieldsCon con fields + = hsep [ptext SLIT("Constructor"), ppr con, + ptext SLIT("does not have field(s):"), pprQuotedList fields] +notSelector field + = hsep [quotes (ppr field), ptext SLIT("is not a record selector")] +\end{code}