X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2FhsSyn%2FHsExpr.lhs;h=f638f657bced5eeb3caeb040e81de97fd795472a;hb=855d87925b0049d23e536c12b9af8e1b545e28f0;hp=78508c85d4b0609c5c68c332e9a5f5b8b49cadcf;hpb=c1500e4888be2341c0b6e6897f494766c86feba0;p=ghc-hetmet.git diff --git a/compiler/hsSyn/HsExpr.lhs b/compiler/hsSyn/HsExpr.lhs index 78508c8..f638f65 100644 --- a/compiler/hsSyn/HsExpr.lhs +++ b/compiler/hsSyn/HsExpr.lhs @@ -2,10 +2,9 @@ % (c) The University of Glasgow 2006 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 % - -HsExpr: Abstract Haskell syntax: expressions - \begin{code} + +-- | Abstract Haskell syntax for expressions. module HsExpr where #include "HsVersions.h" @@ -15,7 +14,6 @@ import HsDecls import HsPat import HsLit import HsTypes -import HsImpExp import HsBinds -- others: @@ -36,14 +34,16 @@ import FastString %************************************************************************ \begin{code} +-- * Expressions proper + type LHsExpr id = Located (HsExpr id) ------------------------- --- PostTcExpr is an evidence expression attached to the --- syntax tree by the type checker (c.f. postTcType) --- We use a PostTcTable where there are a bunch of pieces of --- evidence, more than is convenient to keep individually +-- | PostTcExpr is an evidence expression attached to the syntax tree by the +-- type checker (c.f. postTcType). type PostTcExpr = HsExpr Id +-- | We use a PostTcTable where there are a bunch of pieces of evidence, more +-- than is convenient to keep individually. type PostTcTable = [(Name, Id)] noPostTcExpr :: PostTcExpr @@ -53,11 +53,12 @@ noPostTcTable :: PostTcTable noPostTcTable = [] ------------------------- --- SyntaxExpr is like PostTcExpr, but it's filled in a little earlier, +-- | SyntaxExpr is like 'PostTcExpr', but it's filled in a little earlier, -- by the renamer. It's used for rebindable syntax. --- E.g. (>>=) is filled in before the renamer by the appropriate Name --- for (>>=), and then instantiated by the type checker with its --- type args tec +-- +-- E.g. @(>>=)@ is filled in before the renamer by the appropriate 'Name' for +-- @(>>=)@, and then instantiated by the type checker with its type args +-- tec type SyntaxExpr id = HsExpr id @@ -67,29 +68,33 @@ noSyntaxExpr = HsLit (HsString (fsLit "noSyntaxExpr")) type SyntaxTable id = [(Name, SyntaxExpr id)] --- *** Currently used only for CmdTop (sigh) *** --- * Before the renamer, this list is noSyntaxTable +-- ^ Currently used only for 'CmdTop' (sigh) +-- +-- * Before the renamer, this list is 'noSyntaxTable' -- --- * After the renamer, it takes the form [(std_name, HsVar actual_name)] +-- * After the renamer, it takes the form @[(std_name, HsVar actual_name)]@ -- For example, for the 'return' op of a monad --- normal case: (GHC.Base.return, HsVar GHC.Base.return) --- with rebindable syntax: (GHC.Base.return, return_22) --- where return_22 is whatever "return" is in scope -- --- * After the type checker, it takes the form [(std_name, )] --- where is the evidence for the method +-- * normal case: @(GHC.Base.return, HsVar GHC.Base.return)@ +-- +-- * with rebindable syntax: @(GHC.Base.return, return_22)@ +-- where @return_22@ is whatever @return@ is in scope +-- +-- * After the type checker, it takes the form @[(std_name, )]@ +-- where @@ is the evidence for the method noSyntaxTable :: SyntaxTable id noSyntaxTable = [] ------------------------- +-- | A Haskell expression. data HsExpr id - = HsVar id -- variable - | HsIPVar (IPName id) -- implicit parameter - | HsOverLit (HsOverLit id) -- Overloaded literals + = HsVar id -- ^ variable + | HsIPVar (IPName id) -- ^ implicit parameter + | HsOverLit (HsOverLit id) -- ^ Overloaded literals - | HsLit HsLit -- Simple (non-overloaded) literals + | HsLit HsLit -- ^ Simple (non-overloaded) literals | HsLam (MatchGroup id) -- Currently always a single match @@ -116,6 +121,10 @@ data HsExpr id | SectionR (LHsExpr id) -- operator (LHsExpr id) -- operand + | ExplicitTuple -- Used for explicit tuples and sections thereof + [HsTupArg id] + Boxity + | HsCase (LHsExpr id) (MatchGroup id) @@ -142,14 +151,6 @@ data HsExpr id PostTcType -- type of elements of the parallel array [LHsExpr id] - | ExplicitTuple -- tuple - [LHsExpr id] - -- NB: Unit is ExplicitTuple [] - -- for tuples, we can get the types - -- direct from the components - Boxity - - -- Record construction | RecordCon (Located id) -- The constructor. After type checking -- it's the dataConWrapId of the constructor @@ -159,8 +160,10 @@ data HsExpr id -- Record update | RecordUpd (LHsExpr id) (HsRecordBinds id) +-- (HsMatchGroup Id) -- Filled in by the type checker to be +-- -- a match that does the job [DataCon] -- Filled in by the type checker to the - -- *non-empty* list of DataCons that have + -- _non-empty_ list of DataCons that have -- all the upd'd fields [PostTcType] -- Argument types of *input* record type [PostTcType] -- and *output* record type @@ -198,7 +201,7 @@ data HsExpr id | HsBracketOut (HsBracket Name) -- Output of the type checker is -- the *original* [PendingSplice] -- renamed expression, plus - -- *typechecked* splices to be + -- _typechecked_ splices to be -- pasted back in by the desugarer | HsSpliceE (HsSplice id) @@ -273,6 +276,17 @@ data HsExpr id | HsWrap HsWrapper -- TRANSLATION (HsExpr id) +-- HsTupArg is used for tuple sections +-- (,a,) is represented by ExplicitTuple [Mising ty1, Present a, Missing ty3] +-- Which in turn stands for (\x:ty1 \y:ty2. (x,a,y)) +data HsTupArg id + = Present (LHsExpr id) -- The argument + | Missing PostTcType -- The argument is missing, but this is its type + +tupArgPresent :: HsTupArg id -> Bool +tupArgPresent (Present {}) = True +tupArgPresent (Missing {}) = False + type PendingSplice = (Name, LHsExpr Id) -- Typechecked splices, waiting to be -- pasted back in by the desugarer \end{code} @@ -346,7 +360,7 @@ ppr_expr (OpApp e1 op _ e2) = hang (ppr op) 2 (sep [pp_e1, pp_e2]) pp_infixly v - = sep [nest 2 pp_e1, pprInfix v, nest 2 pp_e2] + = sep [nest 2 pp_e1, pprHsInfix v, nest 2 pp_e2] ppr_expr (NegApp e _) = char '-' <+> pprDebugParendExpr e @@ -359,7 +373,7 @@ ppr_expr (SectionL expr op) pp_prefixly = hang (hsep [text " \\ x_ ->", ppr op]) 4 (hsep [pp_expr, ptext (sLit "x_ )")]) - pp_infixly v = (sep [pp_expr, pprInfix v]) + pp_infixly v = (sep [pp_expr, pprHsInfix v]) ppr_expr (SectionR op expr) = case unLoc op of @@ -371,7 +385,18 @@ ppr_expr (SectionR op expr) pp_prefixly = hang (hsep [text "( \\ x_ ->", ppr op, ptext (sLit "x_")]) 4 ((<>) pp_expr rparen) pp_infixly v - = (sep [pprInfix v, pp_expr]) + = (sep [pprHsInfix v, pp_expr]) + +ppr_expr (ExplicitTuple exprs boxity) + = tupleParens boxity (fcat (ppr_tup_args exprs)) + where + ppr_tup_args [] = [] + ppr_tup_args (Present e : es) = (ppr_lexpr e <> punc es) : ppr_tup_args es + ppr_tup_args (Missing _ : es) = punc es : ppr_tup_args es + + punc (Present {} : _) = comma <> space + punc (Missing {} : _) = comma + punc [] = empty --avoid using PatternSignatures for stage1 code portability ppr_expr exprType@(HsLam matches) @@ -379,8 +404,8 @@ ppr_expr exprType@(HsLam matches) where idType :: HsExpr id -> HsMatchContext id; idType = undefined ppr_expr exprType@(HsCase expr matches) - = sep [ sep [ptext (sLit "case"), nest 4 (ppr expr), ptext (sLit "of")], - nest 2 (pprMatches (CaseAlt `asTypeOf` idType exprType) matches) ] + = sep [ sep [ptext (sLit "case"), nest 4 (ppr expr), ptext (sLit "of {")], + nest 2 (pprMatches (CaseAlt `asTypeOf` idType exprType) matches <+> char '}') ] where idType :: HsExpr id -> HsMatchContext id; idType = undefined ppr_expr (HsIf e1 e2 e3) @@ -406,9 +431,6 @@ ppr_expr (ExplicitList _ exprs) ppr_expr (ExplicitPArr _ exprs) = pa_brackets (pprDeeperList fsep (punctuate comma (map ppr_lexpr exprs))) -ppr_expr (ExplicitTuple exprs boxity) - = tupleParens boxity (sep (punctuate comma (map ppr_lexpr exprs))) - ppr_expr (RecordCon con_id _ rbinds) = hang (ppr con_id) 2 (ppr rbinds) @@ -441,30 +463,30 @@ ppr_expr (HsSpliceE s) = pprSplice s ppr_expr (HsBracket b) = pprHsBracket b ppr_expr (HsBracketOut e []) = ppr e ppr_expr (HsBracketOut e ps) = ppr e $$ ptext (sLit "pending") <+> ppr ps -ppr_expr (HsQuasiQuoteE (HsQuasiQuote name quoter _ quote)) - = char '$' <> brackets (ppr name) <> - ptext (sLit "[:") <> ppr quoter <> ptext (sLit "|") <> - ppr quote <> ptext (sLit "|]") +ppr_expr (HsQuasiQuoteE qq) = ppr qq ppr_expr (HsProc pat (L _ (HsCmdTop cmd _ _ _))) = hsep [ptext (sLit "proc"), ppr pat, ptext (sLit "->"), ppr cmd] ppr_expr (HsTick tickId vars exp) - = hcat [ptext (sLit "tick<"), - ppr tickId, - ptext (sLit ">("), - hsep (map pprHsVar vars), - ppr exp, - ptext (sLit ")")] + = pprTicks (ppr exp) $ + hcat [ptext (sLit "tick<"), + ppr tickId, + ptext (sLit ">("), + hsep (map pprHsVar vars), + ppr exp, + ptext (sLit ")")] ppr_expr (HsBinTick tickIdTrue tickIdFalse exp) - = hcat [ptext (sLit "bintick<"), + = pprTicks (ppr exp) $ + hcat [ptext (sLit "bintick<"), ppr tickIdTrue, ptext (sLit ","), ppr tickIdFalse, ptext (sLit ">("), ppr exp,ptext (sLit ")")] ppr_expr (HsTickPragma externalSrcLoc exp) - = hcat [ptext (sLit "tickpragma<"), + = pprTicks (ppr exp) $ + hcat [ptext (sLit "tickpragma<"), ppr externalSrcLoc, ptext (sLit ">("), ppr exp, @@ -480,7 +502,7 @@ ppr_expr (HsArrApp arrow arg _ HsHigherOrderApp False) = hsep [ppr_lexpr arg, ptext (sLit ">>-"), ppr_lexpr arrow] ppr_expr (HsArrForm (L _ (HsVar v)) (Just _) [arg1, arg2]) - = sep [pprCmdArg (unLoc arg1), hsep [pprInfix v, pprCmdArg (unLoc arg2)]] + = sep [pprCmdArg (unLoc arg1), hsep [pprHsInfix v, pprCmdArg (unLoc arg2)]] ppr_expr (HsArrForm op _ args) = hang (ptext (sLit "(|") <> ppr_lexpr op) 4 (sep (map (pprCmdArg.unLoc) args) <> ptext (sLit "|)")) @@ -494,12 +516,6 @@ pprCmdArg (HsCmdTop cmd _ _ _) instance OutputableBndr id => Outputable (HsCmdTop id) where ppr = pprCmdArg --- Put a var in backquotes if it's not an operator already -pprInfix :: Outputable name => name -> SDoc -pprInfix v | isOperator ppr_v = ppr_v - | otherwise = char '`' <> ppr_v <> char '`' - where ppr_v = ppr v - -- add parallel array brackets around a document -- pa_brackets :: SDoc -> SDoc @@ -531,16 +547,18 @@ pprParendExpr expr -- I think that is usually (always?) right in case unLoc expr of - HsLit _ -> pp_as_was - HsOverLit _ -> pp_as_was - HsVar _ -> pp_as_was - HsIPVar _ -> pp_as_was - ExplicitList _ _ -> pp_as_was - ExplicitPArr _ _ -> pp_as_was - ExplicitTuple _ _ -> pp_as_was - HsPar _ -> pp_as_was - HsBracket _ -> pp_as_was - HsBracketOut _ [] -> pp_as_was + ArithSeq {} -> pp_as_was + PArrSeq {} -> pp_as_was + HsLit {} -> pp_as_was + HsOverLit {} -> pp_as_was + HsVar {} -> pp_as_was + HsIPVar {} -> pp_as_was + ExplicitTuple {} -> pp_as_was + ExplicitList {} -> pp_as_was + ExplicitPArr {} -> pp_as_was + HsPar {} -> pp_as_was + HsBracket {} -> pp_as_was + HsBracketOut _ [] -> pp_as_was HsDo sc _ _ _ | isListCompExpr sc -> pp_as_was _ -> parens pp_as_was @@ -673,9 +691,12 @@ data Match id -- Nothing after typechecking (GRHSs id) +isEmptyMatchGroup :: MatchGroup id -> Bool +isEmptyMatchGroup (MatchGroup ms _) = null ms + matchGroupArity :: MatchGroup id -> Arity matchGroupArity (MatchGroup [] _) - = panic "matchGroupArity" -- MatchGroup is never empty + = panic "matchGroupArity" -- Precondition: MatchGroup is non-empty matchGroupArity (MatchGroup (match:matches) _) = ASSERT( all ((== n_pats) . length . hsLMatchPats) matches ) -- Assertion just checks that all the matches have the same number of pats @@ -686,13 +707,16 @@ matchGroupArity (MatchGroup (match:matches) _) hsLMatchPats :: LMatch id -> [LPat id] hsLMatchPats (L _ (Match pats _ _)) = pats --- GRHSs are used both for pattern bindings and for Matches +-- | GRHSs are used both for pattern bindings and for Matches data GRHSs id - = GRHSs [LGRHS id] -- Guarded RHSs - (HsLocalBinds id) -- The where clause + = GRHSs { + grhssGRHSs :: [LGRHS id], -- ^ Guarded RHSs + grhssLocalBinds :: (HsLocalBinds id) -- ^ The where clause + } type LGRHS id = Located (GRHS id) +-- | Guarded Right Hand Side. data GRHS id = GRHS [LStmt id] -- Guards (LHsExpr id) -- Right hand side \end{code} @@ -753,8 +777,8 @@ pprGRHSs :: (OutputableBndr idL, OutputableBndr idR) => HsMatchContext idL -> GRHSs idR -> SDoc pprGRHSs ctxt (GRHSs grhss binds) = vcat (map (pprGRHS ctxt . unLoc) grhss) - $$ if isEmptyLocalBinds binds then empty - else text "where" $$ nest 4 (pprBinds binds) + $$ ppUnless (isEmptyLocalBinds binds) + (text "where" $$ nest 4 (pprBinds binds)) pprGRHS :: (OutputableBndr idL, OutputableBndr idR) => HsMatchContext idL -> GRHS idR -> SDoc @@ -823,26 +847,38 @@ data StmtLR idL idR -- the names which they group over in statements -- Recursive statement (see Note [RecStmt] below) - | RecStmt [LStmtLR idL idR] - --- The next two fields are only valid after renaming - [idR] -- The ids are a subset of the variables bound by the - -- stmts that are used in stmts that follow the RecStmt - - [idR] -- Ditto, but these variables are the "recursive" ones, - -- that are used before they are bound in the stmts of - -- the RecStmt. From a type-checking point of view, - -- these ones have to be monomorphic - - --- These fields are only valid after typechecking - [PostTcExpr] -- These expressions correspond 1-to-1 with - -- the "recursive" [id], and are the - -- expressions that should be returned by - -- the recursion. - -- They may not quite be the Ids themselves, - -- because the Id may be *polymorphic*, but - -- the returned thing has to be *monomorphic*. - (DictBinds idR) -- Method bindings of Ids bound by the - -- RecStmt, and used afterwards + | RecStmt + { recS_stmts :: [LStmtLR idL idR] + + -- The next two fields are only valid after renaming + , recS_later_ids :: [idR] -- The ids are a subset of the variables bound by the + -- stmts that are used in stmts that follow the RecStmt + + , recS_rec_ids :: [idR] -- Ditto, but these variables are the "recursive" ones, + -- that are used before they are bound in the stmts of + -- the RecStmt. + -- An Id can be in both groups + -- Both sets of Ids are (now) treated monomorphically + -- See Note [How RecStmt works] for why they are separate + + -- Rebindable syntax + , recS_bind_fn :: SyntaxExpr idR -- The bind function + , recS_ret_fn :: SyntaxExpr idR -- The return function + , recS_mfix_fn :: SyntaxExpr idR -- The mfix function + + -- These fields are only valid after typechecking + , recS_rec_rets :: [PostTcExpr] -- These expressions correspond 1-to-1 with + -- recS_rec_ids, and are the + -- expressions that should be returned by + -- the recursion. + -- They may not quite be the Ids themselves, + -- because the Id may be *polymorphic*, but + -- the returned thing has to be *monomorphic*, + -- so they may be type applications + + , recS_dicts :: DictBinds idR -- Method bindings of Ids bound by the + -- RecStmt, and used afterwards + } \end{code} ExprStmts are a bit tricky, because what they mean @@ -870,28 +906,44 @@ depends on the context. Consider the following contexts: Array comprehensions are handled like list comprehensions -=chak -Note [RecStmt] -~~~~~~~~~~~~~~ +Note [How RecStmt works] +~~~~~~~~~~~~~~~~~~~~~~~~ Example: - HsDo [ BindStmt x ex + HsDo [ BindStmt x ex - , RecStmt [a::forall a. a -> a, b] - [a::Int -> Int, c] - [ BindStmt b (return x) - , LetStmt a = ea - , BindStmt c ec ] + , RecStmt { recS_rec_ids = [a, c] + , recS_stmts = [ BindStmt b (return (a,c)) + , LetStmt a = ...b... + , BindStmt c ec ] + , recS_later_ids = [a, b] - , return (a b) ] + , return (a b) ] Here, the RecStmt binds a,b,c; but - Only a,b are used in the stmts *following* the RecStmt, - This 'a' is *polymorphic' - Only a,c are used in the stmts *inside* the RecStmt *before* their bindings - This 'a' is monomorphic -Nota Bene: the two a's have different types, even though they -have the same Name. +Why do we need *both* rec_ids and later_ids? For monads they could be +combined into a single set of variables, but not for arrows. That +follows from the types of the respective feedback operators: + + mfix :: MonadFix m => (a -> m a) -> m a + loop :: ArrowLoop a => a (b,d) (c,d) -> a b c + +* For mfix, the 'a' covers the union of the later_ids and the rec_ids +* For 'loop', 'c' is the later_ids and 'd' is the rec_ids + +Note [Typing a RecStmt] +~~~~~~~~~~~~~~~~~~~~~~~ +A (RecStmt stmts) types as if you had written + + (v1,..,vn, _, ..., _) <- mfix (\~(_, ..., _, r1, ..., rm) -> + do { stmts + ; return (v1,..vn, r1, ..., rm) }) + +where v1..vn are the later_ids + r1..rm are the rec_ids \begin{code} @@ -910,7 +962,11 @@ pprStmt (TransformStmt (stmts, _) usingExpr maybeByExpr) byExprDoc = maybe empty (\byExpr -> hsep [ptext (sLit "by"), ppr byExpr]) maybeByExpr pprStmt (GroupStmt (stmts, _) groupByClause) = (hsep [stmtsDoc, ptext (sLit "then group"), pprGroupByClause groupByClause]) where stmtsDoc = interpp'SP stmts -pprStmt (RecStmt segment _ _ _ _) = ptext (sLit "rec") <+> braces (vcat (map ppr segment)) +pprStmt (RecStmt { recS_stmts = segment, recS_rec_ids = rec_ids, recS_later_ids = later_ids }) + = ptext (sLit "rec") <+> + vcat [ braces (vcat (map ppr segment)) + , ifPprDebug (vcat [ ptext (sLit "rec_ids=") <> ppr rec_ids + , ptext (sLit "later_ids=") <> ppr later_ids])] pprGroupByClause :: (OutputableBndr id) => GroupByClause id -> SDoc pprGroupByClause (GroupByNothing usingExpr) = hsep [ptext (sLit "using"), ppr usingExpr] @@ -918,12 +974,19 @@ pprGroupByClause (GroupBySomething eitherUsingExpr byExpr) = hsep [ptext (sLit " where usingExprDoc = either (\usingExpr -> hsep [ptext (sLit "using"), ppr usingExpr]) (const empty) eitherUsingExpr pprDo :: OutputableBndr id => HsStmtContext any -> [LStmt id] -> LHsExpr id -> SDoc -pprDo DoExpr stmts body = ptext (sLit "do") <+> pprDeeperList vcat (map ppr stmts ++ [ppr body]) -pprDo (MDoExpr _) stmts body = ptext (sLit "mdo") <+> pprDeeperList vcat (map ppr stmts ++ [ppr body]) +pprDo DoExpr stmts body = ptext (sLit "do") <+> ppr_do_stmts stmts body +pprDo (MDoExpr _) stmts body = ptext (sLit "mdo") <+> ppr_do_stmts stmts body pprDo ListComp stmts body = pprComp brackets stmts body pprDo PArrComp stmts body = pprComp pa_brackets stmts body pprDo _ _ _ = panic "pprDo" -- PatGuard, ParStmtCxt +ppr_do_stmts :: OutputableBndr id => [LStmt id] -> LHsExpr id -> SDoc +-- Print a bunch of do stmts, with explicit braces and semicolons, +-- so that we are not vulnerable to layout bugs +ppr_do_stmts stmts body + = lbrace <+> pprDeeperList vcat ([ ppr s <> semi | s <- stmts] ++ [ppr body]) + <+> rbrace + pprComp :: OutputableBndr id => (SDoc -> SDoc) -> [LStmt id] -> LHsExpr id -> SDoc pprComp brack quals body = brack $ @@ -1016,10 +1079,10 @@ pp_dotdot = ptext (sLit " .. ") \begin{code} data HsMatchContext id -- Context of a Match = FunRhs id Bool -- Function binding for f; True <=> written infix - | CaseAlt -- Guard on a case alternative - | LambdaExpr -- Pattern of a lambda - | ProcExpr -- Pattern of a proc - | PatBindRhs -- Pattern binding + | CaseAlt -- Patterns and guards on a case alternative + | LambdaExpr -- Patterns of a lambda + | ProcExpr -- Patterns of a proc + | PatBindRhs -- Patterns in the *guards* of a pattern binding | RecUpd -- Record update [used only in DsExpr to -- tell matchWrapper what sort of -- runtime error message to generate] @@ -1101,20 +1164,20 @@ pprStmtResultContext other = ptext (sLit "the result of") <+> pprStmtC -} -- Used to generate the string for a *runtime* error message -matchContextErrString :: Outputable id => HsMatchContext id -> String -matchContextErrString (FunRhs fun _) = "function " ++ showSDoc (ppr fun) -matchContextErrString CaseAlt = "case" -matchContextErrString PatBindRhs = "pattern binding" -matchContextErrString RecUpd = "record update" -matchContextErrString LambdaExpr = "lambda" -matchContextErrString ProcExpr = "proc" +matchContextErrString :: Outputable id => HsMatchContext id -> SDoc +matchContextErrString (FunRhs fun _) = ptext (sLit "function") <+> ppr fun +matchContextErrString CaseAlt = ptext (sLit "case") +matchContextErrString PatBindRhs = ptext (sLit "pattern binding") +matchContextErrString RecUpd = ptext (sLit "record update") +matchContextErrString LambdaExpr = ptext (sLit "lambda") +matchContextErrString ProcExpr = ptext (sLit "proc") matchContextErrString (StmtCtxt (ParStmtCtxt c)) = matchContextErrString (StmtCtxt c) matchContextErrString (StmtCtxt (TransformStmtCtxt c)) = matchContextErrString (StmtCtxt c) -matchContextErrString (StmtCtxt (PatGuard _)) = "pattern guard" -matchContextErrString (StmtCtxt DoExpr) = "'do' expression" -matchContextErrString (StmtCtxt (MDoExpr _)) = "'mdo' expression" -matchContextErrString (StmtCtxt ListComp) = "list comprehension" -matchContextErrString (StmtCtxt PArrComp) = "array comprehension" +matchContextErrString (StmtCtxt (PatGuard _)) = ptext (sLit "pattern guard") +matchContextErrString (StmtCtxt DoExpr) = ptext (sLit "'do' expression") +matchContextErrString (StmtCtxt (MDoExpr _)) = ptext (sLit "'mdo' expression") +matchContextErrString (StmtCtxt ListComp) = ptext (sLit "list comprehension") +matchContextErrString (StmtCtxt PArrComp) = ptext (sLit "array comprehension") \end{code} \begin{code}