% % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 % \section[RnExpr]{Renaming of expressions} Basically dependency analysis. Handles @Match@, @GRHSs@, @HsExpr@, and @Qualifier@ datatypes. In general, all of these functions return a renamed thing, and a set of free variables. \begin{code}

    module RnExpr (
    	rnLExpr, rnExpr, rnStmts
       ) where

    #include "HsVersions.h"

    #ifdef GHCI
    import {-# SOURCE #-} TcSplice( runQuasiQuoteExpr )
    #endif 	/* GHCI */

    import RnSource  ( rnSrcDecls, findSplice )
    import RnBinds   ( rnLocalBindsAndThen, rnLocalValBindsLHS, rnLocalValBindsRHS,
                       rnMatchGroup, makeMiniFixityEnv)
    import HsSyn
    import TcRnMonad
    import TcEnv		( thRnBrack )
    import RnEnv
    import RnTypes		( rnHsTypeFVs, rnSplice, checkTH,
    			  mkOpFormRn, mkOpAppRn, mkNegAppRn, checkSectionPrec)
    import RnPat
    import DynFlags
    import BasicTypes	( FixityDirection(..) )
    import PrelNames

    import Name
    import NameSet
    import RdrName
    import LoadIface	( loadInterfaceForName )
    import UniqSet
    import Data.List
    import Util		( isSingleton )
    import ListSetOps	( removeDups )
    import Outputable
    import SrcLoc
    import FastString
    import Control.Monad

\end{code} \begin{code}

    -- XXX
    thenM :: Monad a => a b -> (b -> a c) -> a c
    thenM = (>>=)

    thenM_ :: Monad a => a b -> a c -> a c
    thenM_ = (>>)

\end{code} %************************************************************************ %* * \subsubsection{Expressions} %* * %************************************************************************ \begin{code}

    rnExprs :: [LHsExpr RdrName] -> RnM ([LHsExpr Name], FreeVars)
    rnExprs ls = rnExprs' ls emptyUniqSet
     where
      rnExprs' [] acc = return ([], acc)
      rnExprs' (expr:exprs) acc
       = rnLExpr expr 	        `thenM` \ (expr', fvExpr) ->

    	-- Now we do a "seq" on the free vars because typically it's small
    	-- or empty, especially in very long lists of constants
        let
    	acc' = acc `plusFV` fvExpr
        in
        acc' `seq` rnExprs' exprs acc' `thenM` \ (exprs', fvExprs) ->
        return (expr':exprs', fvExprs)

\end{code} Variables. We look up the variable and return the resulting name. \begin{code}

    rnLExpr :: LHsExpr RdrName -> RnM (LHsExpr Name, FreeVars)
    rnLExpr = wrapLocFstM rnExpr

    rnExpr :: HsExpr RdrName -> RnM (HsExpr Name, FreeVars)

    finishHsVar :: Name -> RnM (HsExpr Name, FreeVars)
    -- Separated from rnExpr because it's also used
    -- when renaming infix expressions
    -- See Note [Adding the implicit parameter to 'assert']
    finishHsVar name
     = do { ignore_asserts <- doptM Opt_IgnoreAsserts
          ; if ignore_asserts || not (name `hasKey` assertIdKey)
    	then return (HsVar name, unitFV name)
    	else do { e <- mkAssertErrorExpr
    		; return (e, unitFV name) } }

    rnExpr (HsVar v)
      = do name <- lookupOccRn v
           finishHsVar name

    rnExpr (HsIPVar v)
      = newIPNameRn v		`thenM` \ name ->
        return (HsIPVar name, emptyFVs)

    rnExpr (HsLit lit@(HsString s))
      = do {
             opt_OverloadedStrings <- xoptM Opt_OverloadedStrings
           ; if opt_OverloadedStrings then
                rnExpr (HsOverLit (mkHsIsString s placeHolderType))
    	 else -- Same as below
    	    rnLit lit		`thenM_`
                return (HsLit lit, emptyFVs)
           }

    rnExpr (HsLit lit)
      = rnLit lit		`thenM_`
        return (HsLit lit, emptyFVs)

    rnExpr (HsOverLit lit)
      = rnOverLit lit		`thenM` \ (lit', fvs) ->
        return (HsOverLit lit', fvs)

    rnExpr (HsApp fun arg)
      = rnLExpr fun		`thenM` \ (fun',fvFun) ->
        rnLExpr arg		`thenM` \ (arg',fvArg) ->
        return (HsApp fun' arg', fvFun `plusFV` fvArg)

    rnExpr (OpApp e1 (L op_loc (HsVar op_rdr)) _ e2)
      = do  { (e1', fv_e1) <- rnLExpr e1
    	; (e2', fv_e2) <- rnLExpr e2
    	; op_name <- setSrcSpan op_loc (lookupOccRn op_rdr)
      	; (op', fv_op) <- finishHsVar op_name
    		-- NB: op' is usually just a variable, but might be
    		--     an applicatoin (assert "Foo.hs:47")
    	-- Deal with fixity
    	-- When renaming code synthesised from "deriving" declarations
    	-- we used to avoid fixity stuff, but we can't easily tell any
    	-- more, so I've removed the test.  Adding HsPars in TcGenDeriv
    	-- should prevent bad things happening.
    	; fixity <- lookupFixityRn op_name
    	; final_e <- mkOpAppRn e1' (L op_loc op') fixity e2'
    	; return (final_e, fv_e1 `plusFV` fv_op `plusFV` fv_e2) }
    rnExpr (OpApp _ other_op _ _)
      = failWith (vcat [ hang (ptext (sLit "Operator application with a non-variable operator:"))
                            2 (ppr other_op)
                       , ptext (sLit "(Probably resulting from a Template Haskell splice)") ])

    rnExpr (NegApp e _)
      = rnLExpr e			`thenM` \ (e', fv_e) ->
        lookupSyntaxName negateName	`thenM` \ (neg_name, fv_neg) ->
        mkNegAppRn e' neg_name	`thenM` \ final_e ->
        return (final_e, fv_e `plusFV` fv_neg)

    ------------------------------------------
    -- Template Haskell extensions
    -- Don't ifdef-GHCI them because we want to fail gracefully
    -- (not with an rnExpr crash) in a stage-1 compiler.
    rnExpr e@(HsBracket br_body)
      = checkTH e "bracket"		`thenM_`
        rnBracket br_body		`thenM` \ (body', fvs_e) ->
        return (HsBracket body', fvs_e)

    rnExpr (HsSpliceE splice)
      = rnSplice splice 		`thenM` \ (splice', fvs) ->
        return (HsSpliceE splice', fvs)

    #ifndef GHCI
    rnExpr e@(HsQuasiQuoteE _) = pprPanic "Cant do quasiquotation without GHCi" (ppr e)
    #else
    rnExpr (HsQuasiQuoteE qq)
      = runQuasiQuoteExpr qq	`thenM` \ (L _ expr') ->
        rnExpr expr'
    #endif 	/* GHCI */

    ---------------------------------------------
    --	Sections
    -- See Note [Parsing sections] in Parser.y.pp
    rnExpr (HsPar (L loc (section@(SectionL {}))))
      = do	{ (section', fvs) <- rnSection section
    	; return (HsPar (L loc section'), fvs) }

    rnExpr (HsPar (L loc (section@(SectionR {}))))
      = do	{ (section', fvs) <- rnSection section
    	; return (HsPar (L loc section'), fvs) }

    rnExpr (HsPar e)
      = do	{ (e', fvs_e) <- rnLExpr e
    	; return (HsPar e', fvs_e) }

    rnExpr expr@(SectionL {})
      = do	{ addErr (sectionErr expr); rnSection expr }
    rnExpr expr@(SectionR {})
      = do	{ addErr (sectionErr expr); rnSection expr }

    ---------------------------------------------
    rnExpr (HsCoreAnn ann expr)
      = rnLExpr expr `thenM` \ (expr', fvs_expr) ->
        return (HsCoreAnn ann expr', fvs_expr)

    rnExpr (HsSCC lbl expr)
      = rnLExpr expr	 	`thenM` \ (expr', fvs_expr) ->
        return (HsSCC lbl expr', fvs_expr)
    rnExpr (HsTickPragma info expr)
      = rnLExpr expr	 	`thenM` \ (expr', fvs_expr) ->
        return (HsTickPragma info expr', fvs_expr)

    rnExpr (HsLam matches)
      = rnMatchGroup LambdaExpr matches	`thenM` \ (matches', fvMatch) ->
        return (HsLam matches', fvMatch)

    rnExpr (HsCase expr matches)
      = rnLExpr expr		 	`thenM` \ (new_expr, e_fvs) ->
        rnMatchGroup CaseAlt matches	`thenM` \ (new_matches, ms_fvs) ->
        return (HsCase new_expr new_matches, e_fvs `plusFV` ms_fvs)

    rnExpr (HsLet binds expr)
      = rnLocalBindsAndThen binds		$ \ binds' ->
        rnLExpr expr			 `thenM` \ (expr',fvExpr) ->
        return (HsLet binds' expr', fvExpr)

    rnExpr (HsDo do_or_lc stmts body _)
      = do 	{ ((stmts', body'), fvs) <- rnStmts do_or_lc stmts $
    				    rnLExpr body
    	; return (HsDo do_or_lc stmts' body' placeHolderType, fvs) }

    rnExpr (ExplicitList _ exps)
      = rnExprs exps		 	`thenM` \ (exps', fvs) ->
        return  (ExplicitList placeHolderType exps', fvs)

    rnExpr (ExplicitPArr _ exps)
      = rnExprs exps		 	`thenM` \ (exps', fvs) ->
        return  (ExplicitPArr placeHolderType exps', fvs)

    rnExpr (ExplicitTuple tup_args boxity)
      = do { checkTupleSection tup_args
           ; checkTupSize (length tup_args)
           ; (tup_args', fvs) <- mapAndUnzipM rnTupArg tup_args
           ; return (ExplicitTuple tup_args' boxity, plusFVs fvs) }
      where
        rnTupArg (Present e) = do { (e',fvs) <- rnLExpr e; return (Present e', fvs) }
        rnTupArg (Missing _) = return (Missing placeHolderType, emptyFVs)

    rnExpr (RecordCon con_id _ rbinds)
      = do	{ conname <- lookupLocatedOccRn con_id
    	; (rbinds', fvRbinds) <- rnHsRecBinds (HsRecFieldCon (unLoc conname)) rbinds
    	; return (RecordCon conname noPostTcExpr rbinds',
    		  fvRbinds `addOneFV` unLoc conname) }

    rnExpr (RecordUpd expr rbinds _ _ _)
      = do	{ (expr', fvExpr) <- rnLExpr expr
    	; (rbinds', fvRbinds) <- rnHsRecBinds HsRecFieldUpd rbinds
    	; return (RecordUpd expr' rbinds' [] [] [],
    		  fvExpr `plusFV` fvRbinds) }

    rnExpr (ExprWithTySig expr pty)
      = do	{ (pty', fvTy) <- rnHsTypeFVs doc pty
    	; (expr', fvExpr) <- bindSigTyVarsFV (hsExplicitTvs pty') $
    		  	     rnLExpr expr
    	; return (ExprWithTySig expr' pty', fvExpr `plusFV` fvTy) }
      where
        doc = text "In an expression type signature"

    rnExpr (HsIf _ p b1 b2)
      = do { (p', fvP) <- rnLExpr p
        ; (b1', fvB1) <- rnLExpr b1
        ; (b2', fvB2) <- rnLExpr b2
        ; rebind <- xoptM Opt_RebindableSyntax
        ; if not rebind
           then return (HsIf Nothing p' b1' b2', plusFVs [fvP, fvB1, fvB2])
           else do { c <- liftM HsVar (lookupOccRn (mkVarUnqual (fsLit "ifThenElse")))
                   ; return (HsIf (Just c) p' b1' b2', plusFVs [fvP, fvB1, fvB2]) }}

    rnExpr (HsType a)
      = rnHsTypeFVs doc a	`thenM` \ (t, fvT) ->
        return (HsType t, fvT)
      where
        doc = text "In a type argument"

    rnExpr (ArithSeq _ seq)
      = rnArithSeq seq	 `thenM` \ (new_seq, fvs) ->
        return (ArithSeq noPostTcExpr new_seq, fvs)

    rnExpr (PArrSeq _ seq)
      = rnArithSeq seq	 `thenM` \ (new_seq, fvs) ->
        return (PArrSeq noPostTcExpr new_seq, fvs)

\end{code} These three are pattern syntax appearing in expressions. Since all the symbols are reservedops we can simply reject them. We return a (bogus) EWildPat in each case. \begin{code}

    rnExpr e@EWildPat      = patSynErr e
    rnExpr e@(EAsPat {})   = patSynErr e
    rnExpr e@(EViewPat {}) = patSynErr e
    rnExpr e@(ELazyPat {}) = patSynErr e

\end{code} %************************************************************************ %* * Arrow notation %* * %************************************************************************ \begin{code}

    rnExpr (HsProc pat body)
      = newArrowScope $
        rnPat ProcExpr pat $ \ pat' ->
        rnCmdTop body	         `thenM` \ (body',fvBody) ->
        return (HsProc pat' body', fvBody)

    rnExpr (HsArrApp arrow arg _ ho rtl)
      = select_arrow_scope (rnLExpr arrow)	`thenM` \ (arrow',fvArrow) ->
        rnLExpr arg				`thenM` \ (arg',fvArg) ->
        return (HsArrApp arrow' arg' placeHolderType ho rtl,
    	     fvArrow `plusFV` fvArg)
      where
        select_arrow_scope tc = case ho of
            HsHigherOrderApp -> tc
            HsFirstOrderApp  -> escapeArrowScope tc

    -- infix form
    rnExpr (HsArrForm op (Just _) [arg1, arg2])
      = escapeArrowScope (rnLExpr op)
    			`thenM` \ (op',fv_op) ->
        let L _ (HsVar op_name) = op' in
        rnCmdTop arg1	`thenM` \ (arg1',fv_arg1) ->
        rnCmdTop arg2	`thenM` \ (arg2',fv_arg2) ->

    	-- Deal with fixity

        lookupFixityRn op_name		`thenM` \ fixity ->
        mkOpFormRn arg1' op' fixity arg2'	`thenM` \ final_e ->

        return (final_e,
    	      fv_arg1 `plusFV` fv_op `plusFV` fv_arg2)

    rnExpr (HsArrForm op fixity cmds)
      = escapeArrowScope (rnLExpr op)	`thenM` \ (op',fvOp) ->
        rnCmdArgs cmds			`thenM` \ (cmds',fvCmds) ->
        return (HsArrForm op' fixity cmds', fvOp `plusFV` fvCmds)

    rnExpr other = pprPanic "rnExpr: unexpected expression" (ppr other)
    	-- HsWrap

    ----------------------
    -- See Note [Parsing sections] in Parser.y.pp
    rnSection :: HsExpr RdrName -> RnM (HsExpr Name, FreeVars)
    rnSection section@(SectionR op expr)
      = do	{ (op', fvs_op)     <- rnLExpr op
    	; (expr', fvs_expr) <- rnLExpr expr
    	; checkSectionPrec InfixR section op' expr'
    	; return (SectionR op' expr', fvs_op `plusFV` fvs_expr) }

    rnSection section@(SectionL expr op)
      = do	{ (expr', fvs_expr) <- rnLExpr expr
    	; (op', fvs_op)     <- rnLExpr op
    	; checkSectionPrec InfixL section op' expr'
    	; return (SectionL expr' op', fvs_op `plusFV` fvs_expr) }

    rnSection other = pprPanic "rnSection" (ppr other)

\end{code} %************************************************************************ %* * Records %* * %************************************************************************ \begin{code}

    rnHsRecBinds :: HsRecFieldContext -> HsRecordBinds RdrName
                 -> RnM (HsRecordBinds Name, FreeVars)
    rnHsRecBinds ctxt rec_binds@(HsRecFields { rec_dotdot = dd })
      = do { (flds, fvs) <- rnHsRecFields1 ctxt HsVar rec_binds
           ; (flds', fvss) <- mapAndUnzipM rn_field flds
           ; return (HsRecFields { rec_flds = flds', rec_dotdot = dd },
                     fvs `plusFV` plusFVs fvss) }
      where
        rn_field fld = do { (arg', fvs) <- rnLExpr (hsRecFieldArg fld)
                          ; return (fld { hsRecFieldArg = arg' }, fvs) }

\end{code} %************************************************************************ %* * Arrow commands %* * %************************************************************************ \begin{code}

    rnCmdArgs :: [LHsCmdTop RdrName] -> RnM ([LHsCmdTop Name], FreeVars)
    rnCmdArgs [] = return ([], emptyFVs)
    rnCmdArgs (arg:args)
      = rnCmdTop arg	`thenM` \ (arg',fvArg) ->
        rnCmdArgs args	`thenM` \ (args',fvArgs) ->
        return (arg':args', fvArg `plusFV` fvArgs)

    rnCmdTop :: LHsCmdTop RdrName -> RnM (LHsCmdTop Name, FreeVars)
    rnCmdTop = wrapLocFstM rnCmdTop'
     where
      rnCmdTop' (HsCmdTop cmd _ _ _)
       = rnLExpr (convertOpFormsLCmd cmd) `thenM` \ (cmd', fvCmd) ->
         let
    	cmd_names = [arrAName, composeAName, firstAName] ++
    		    nameSetToList (methodNamesCmd (unLoc cmd'))
         in
    	-- Generate the rebindable syntax for the monad
         lookupSyntaxTable cmd_names	`thenM` \ (cmd_names', cmd_fvs) ->

         return (HsCmdTop cmd' [] placeHolderType cmd_names',
    	     fvCmd `plusFV` cmd_fvs)

    ---------------------------------------------------
    -- convert OpApp's in a command context to HsArrForm's

    convertOpFormsLCmd :: LHsCmd id -> LHsCmd id
    convertOpFormsLCmd = fmap convertOpFormsCmd

    convertOpFormsCmd :: HsCmd id -> HsCmd id

    convertOpFormsCmd (HsApp c e) = HsApp (convertOpFormsLCmd c) e
    convertOpFormsCmd (HsLam match) = HsLam (convertOpFormsMatch match)
    convertOpFormsCmd (OpApp c1 op fixity c2)
      = let
    	arg1 = L (getLoc c1) $ HsCmdTop (convertOpFormsLCmd c1) [] placeHolderType []
    	arg2 = L (getLoc c2) $ HsCmdTop (convertOpFormsLCmd c2) [] placeHolderType []
        in
        HsArrForm op (Just fixity) [arg1, arg2]

    convertOpFormsCmd (HsPar c) = HsPar (convertOpFormsLCmd c)

    convertOpFormsCmd (HsCase exp matches)
      = HsCase exp (convertOpFormsMatch matches)

    convertOpFormsCmd (HsIf f exp c1 c2)
      = HsIf f exp (convertOpFormsLCmd c1) (convertOpFormsLCmd c2)

    convertOpFormsCmd (HsLet binds cmd)
      = HsLet binds (convertOpFormsLCmd cmd)

    convertOpFormsCmd (HsDo ctxt stmts body ty)
      = HsDo ctxt (map (fmap convertOpFormsStmt) stmts)
    	      (convertOpFormsLCmd body) ty

    -- Anything else is unchanged.  This includes HsArrForm (already done),
    -- things with no sub-commands, and illegal commands (which will be
    -- caught by the type checker)
    convertOpFormsCmd c = c

    convertOpFormsStmt :: StmtLR id id -> StmtLR id id
    convertOpFormsStmt (BindStmt pat cmd _ _)
      = BindStmt pat (convertOpFormsLCmd cmd) noSyntaxExpr noSyntaxExpr
    convertOpFormsStmt (ExprStmt cmd _ _)
      = ExprStmt (convertOpFormsLCmd cmd) noSyntaxExpr placeHolderType
    convertOpFormsStmt stmt@(RecStmt { recS_stmts = stmts })
      = stmt { recS_stmts = map (fmap convertOpFormsStmt) stmts }
    convertOpFormsStmt stmt = stmt

    convertOpFormsMatch :: MatchGroup id -> MatchGroup id
    convertOpFormsMatch (MatchGroup ms ty)
      = MatchGroup (map (fmap convert) ms) ty
     where convert (Match pat mty grhss)
    	  = Match pat mty (convertOpFormsGRHSs grhss)

    convertOpFormsGRHSs :: GRHSs id -> GRHSs id
    convertOpFormsGRHSs (GRHSs grhss binds)
      = GRHSs (map convertOpFormsGRHS grhss) binds

    convertOpFormsGRHS :: Located (GRHS id) -> Located (GRHS id)
    convertOpFormsGRHS = fmap convert
     where
       convert (GRHS stmts cmd) = GRHS stmts (convertOpFormsLCmd cmd)

    ---------------------------------------------------
    type CmdNeeds = FreeVars	-- Only inhabitants are
    				-- 	appAName, choiceAName, loopAName

    -- find what methods the Cmd needs (loop, choice, apply)
    methodNamesLCmd :: LHsCmd Name -> CmdNeeds
    methodNamesLCmd = methodNamesCmd . unLoc

    methodNamesCmd :: HsCmd Name -> CmdNeeds

    methodNamesCmd (HsArrApp _arrow _arg _ HsFirstOrderApp _rtl)
      = emptyFVs
    methodNamesCmd (HsArrApp _arrow _arg _ HsHigherOrderApp _rtl)
      = unitFV appAName
    methodNamesCmd (HsArrForm {}) = emptyFVs

    methodNamesCmd (HsPar c) = methodNamesLCmd c

    methodNamesCmd (HsIf _ _ c1 c2)
      = methodNamesLCmd c1 `plusFV` methodNamesLCmd c2 `addOneFV` choiceAName

    methodNamesCmd (HsLet _ c) = methodNamesLCmd c

    methodNamesCmd (HsDo _ stmts body _)
      = methodNamesStmts stmts `plusFV` methodNamesLCmd body

    methodNamesCmd (HsApp c _) = methodNamesLCmd c

    methodNamesCmd (HsLam match) = methodNamesMatch match

    methodNamesCmd (HsCase _ matches)
      = methodNamesMatch matches `addOneFV` choiceAName

    methodNamesCmd _ = emptyFVs
       -- Other forms can't occur in commands, but it's not convenient
       -- to error here so we just do what's convenient.
       -- The type checker will complain later

    ---------------------------------------------------
    methodNamesMatch :: MatchGroup Name -> FreeVars
    methodNamesMatch (MatchGroup ms _)
      = plusFVs (map do_one ms)
     where
        do_one (L _ (Match _ _ grhss)) = methodNamesGRHSs grhss

    -------------------------------------------------
    -- gaw 2004
    methodNamesGRHSs :: GRHSs Name -> FreeVars
    methodNamesGRHSs (GRHSs grhss _) = plusFVs (map methodNamesGRHS grhss)

    -------------------------------------------------

    methodNamesGRHS :: Located (GRHS Name) -> CmdNeeds
    methodNamesGRHS (L _ (GRHS _ rhs)) = methodNamesLCmd rhs

    ---------------------------------------------------
    methodNamesStmts :: [Located (StmtLR Name Name)] -> FreeVars
    methodNamesStmts stmts = plusFVs (map methodNamesLStmt stmts)

    ---------------------------------------------------
    methodNamesLStmt :: Located (StmtLR Name Name) -> FreeVars
    methodNamesLStmt = methodNamesStmt . unLoc

    methodNamesStmt :: StmtLR Name Name -> FreeVars
    methodNamesStmt (ExprStmt cmd _ _)               = methodNamesLCmd cmd
    methodNamesStmt (BindStmt _ cmd _ _)             = methodNamesLCmd cmd
    methodNamesStmt (RecStmt { recS_stmts = stmts }) = methodNamesStmts stmts `addOneFV` loopAName
    methodNamesStmt (LetStmt _)                      = emptyFVs
    methodNamesStmt (ParStmt _)                      = emptyFVs
    methodNamesStmt (TransformStmt {})               = emptyFVs
    methodNamesStmt (GroupStmt {})                   = emptyFVs
       -- ParStmt, TransformStmt and GroupStmt can't occur in commands, but it's not convenient to error
       -- here so we just do what's convenient

\end{code} %************************************************************************ %* * Arithmetic sequences %* * %************************************************************************ \begin{code}

    rnArithSeq :: ArithSeqInfo RdrName -> RnM (ArithSeqInfo Name, FreeVars)
    rnArithSeq (From expr)
     = rnLExpr expr 	`thenM` \ (expr', fvExpr) ->
       return (From expr', fvExpr)

    rnArithSeq (FromThen expr1 expr2)
     = rnLExpr expr1 	`thenM` \ (expr1', fvExpr1) ->
       rnLExpr expr2	`thenM` \ (expr2', fvExpr2) ->
       return (FromThen expr1' expr2', fvExpr1 `plusFV` fvExpr2)

    rnArithSeq (FromTo expr1 expr2)
     = rnLExpr expr1	`thenM` \ (expr1', fvExpr1) ->
       rnLExpr expr2	`thenM` \ (expr2', fvExpr2) ->
       return (FromTo expr1' expr2', fvExpr1 `plusFV` fvExpr2)

    rnArithSeq (FromThenTo expr1 expr2 expr3)
     = rnLExpr expr1	`thenM` \ (expr1', fvExpr1) ->
       rnLExpr expr2	`thenM` \ (expr2', fvExpr2) ->
       rnLExpr expr3	`thenM` \ (expr3', fvExpr3) ->
       return (FromThenTo expr1' expr2' expr3',
    	    plusFVs [fvExpr1, fvExpr2, fvExpr3])

\end{code} %************************************************************************ %* * Template Haskell brackets %* * %************************************************************************ \begin{code}

    rnBracket :: HsBracket RdrName -> RnM (HsBracket Name, FreeVars)
    rnBracket (VarBr n) = do { name <- lookupOccRn n
    			 ; this_mod <- getModule
    			 ; unless (nameIsLocalOrFrom this_mod name) $	-- Reason: deprecation checking asumes the
    			   do { _ <- loadInterfaceForName msg name	-- home interface is loaded, and this is the
    			      ; return () }				-- only way that is going to happen
    			 ; return (VarBr name, unitFV name) }
    		    where
    		      msg = ptext (sLit "Need interface for Template Haskell quoted Name")

    rnBracket (ExpBr e) = do { (e', fvs) <- rnLExpr e
    			 ; return (ExpBr e', fvs) }

    rnBracket (PatBr p) = rnPat ThPatQuote p $ \ p' -> return (PatBr p', emptyFVs)

    rnBracket (TypBr t) = do { (t', fvs) <- rnHsTypeFVs doc t
    			 ; return (TypBr t', fvs) }
    		    where
    		      doc = ptext (sLit "In a Template-Haskell quoted type")

    rnBracket (DecBrL decls)
      = do { (group, mb_splice) <- findSplice decls
           ; case mb_splice of
               Nothing -> return ()
               Just (SpliceDecl (L loc _) _, _)
                  -> setSrcSpan loc $
                     addErr (ptext (sLit "Declaration splices are not permitted inside declaration brackets"))
    		-- Why not?  See Section 7.3 of the TH paper.

           ; gbl_env  <- getGblEnv
           ; let new_gbl_env = gbl_env { tcg_dus = emptyDUs }
    	      		  -- The emptyDUs is so that we just collect uses for this
                              -- group alone in the call to rnSrcDecls below
           ; (tcg_env, group') <- setGblEnv new_gbl_env $
           	 	   	      setStage thRnBrack $
    			      rnSrcDecls group

    	      -- Discard the tcg_env; it contains only extra info about fixity
            ; traceRn (text "rnBracket dec" <+> (ppr (tcg_dus tcg_env) $$ ppr (duUses (tcg_dus tcg_env))))
    	; return (DecBrG group', duUses (tcg_dus tcg_env)) }

    rnBracket (DecBrG _) = panic "rnBracket: unexpected DecBrG"

\end{code} %************************************************************************ %* * \subsubsection{@Stmt@s: in @do@ expressions} %* * %************************************************************************ \begin{code}

    rnStmts :: HsStmtContext Name -> [LStmt RdrName]
    	-> RnM (thing, FreeVars)
    	-> RnM (([LStmt Name], thing), FreeVars)
    -- Variables bound by the Stmts, and mentioned in thing_inside,
    -- do not appear in the result FreeVars

    rnStmts (MDoExpr _) stmts thing_inside = rnMDoStmts    stmts thing_inside
    rnStmts ctxt        stmts thing_inside = rnNormalStmts ctxt stmts (\ _ -> thing_inside)

    rnNormalStmts :: HsStmtContext Name -> [LStmt RdrName]
    	      -> ([Name] -> RnM (thing, FreeVars))
    	      -> RnM (([LStmt Name], thing), FreeVars)
    -- Variables bound by the Stmts, and mentioned in thing_inside,
    -- do not appear in the result FreeVars
    --
    -- Renaming a single RecStmt can give a sequence of smaller Stmts

    rnNormalStmts _ [] thing_inside
      = do { (res, fvs) <- thing_inside []
           ; return (([], res), fvs) }

    rnNormalStmts ctxt (stmt@(L loc _) : stmts) thing_inside
      = do { ((stmts1, (stmts2, thing)), fvs)
                <- setSrcSpan loc           $
                   rnStmt ctxt stmt         $ \ bndrs1 ->
                   rnNormalStmts ctxt stmts $ \ bndrs2 ->
                   thing_inside (bndrs1 ++ bndrs2)
    	; return (((stmts1 ++ stmts2), thing), fvs) }

    rnStmt :: HsStmtContext Name -> LStmt RdrName
           -> ([Name] -> RnM (thing, FreeVars))
           -> RnM (([LStmt Name], thing), FreeVars)
    -- Variables bound by the Stmt, and mentioned in thing_inside,
    -- do not appear in the result FreeVars

    rnStmt _ (L loc (ExprStmt expr _ _)) thing_inside
      = do	{ (expr', fv_expr) <- rnLExpr expr
    	; (then_op, fvs1)  <- lookupSyntaxName thenMName
    	; (thing, fvs2)    <- thing_inside []
    	; return (([L loc (ExprStmt expr' then_op placeHolderType)], thing),
    		  fv_expr `plusFV` fvs1 `plusFV` fvs2) }

    rnStmt ctxt (L loc (BindStmt pat expr _ _)) thing_inside
      = do	{ (expr', fv_expr) <- rnLExpr expr
    		-- The binders do not scope over the expression
    	; (bind_op, fvs1) <- lookupSyntaxName bindMName
    	; (fail_op, fvs2) <- lookupSyntaxName failMName
    	; rnPat (StmtCtxt ctxt) pat $ \ pat' -> do
    	{ (thing, fvs3) <- thing_inside (collectPatBinders pat')
    	; return (([L loc (BindStmt pat' expr' bind_op fail_op)], thing),
    		  fv_expr `plusFV` fvs1 `plusFV` fvs2 `plusFV` fvs3) }}
           -- fv_expr shouldn't really be filtered by the rnPatsAndThen
    	-- but it does not matter because the names are unique

    rnStmt ctxt (L loc (LetStmt binds)) thing_inside
      = do	{ checkLetStmt ctxt binds
    	; rnLocalBindsAndThen binds $ \binds' -> do
    	{ (thing, fvs) <- thing_inside (collectLocalBinders binds')
            ; return (([L loc (LetStmt binds')], thing), fvs) }  }

    rnStmt ctxt (L _ (RecStmt { recS_stmts = rec_stmts })) thing_inside
      = do	{ checkRecStmt ctxt

    	-- Step1: Bring all the binders of the mdo into scope
    	-- (Remember that this also removes the binders from the
    	-- finally-returned free-vars.)
       	-- And rename each individual stmt, making a
    	-- singleton segment.  At this stage the FwdRefs field
    	-- isn't finished: it's empty for all except a BindStmt
    	-- for which it's the fwd refs within the bind itself
    	-- (This set may not be empty, because we're in a recursive
    	-- context.)
            ; rn_rec_stmts_and_then rec_stmts	$ \ segs -> do

    	{ let bndrs = nameSetToList $ foldr (unionNameSets . (\(ds,_,_,_) -> ds))
                                                emptyNameSet segs
            ; (thing, fvs_later) <- thing_inside bndrs
    	; (return_op, fvs1)  <- lookupSyntaxName returnMName
    	; (mfix_op,   fvs2)  <- lookupSyntaxName mfixName
    	; (bind_op,   fvs3)  <- lookupSyntaxName bindMName
    	; let
    		-- Step 2: Fill in the fwd refs.
    		-- 	   The segments are all singletons, but their fwd-ref
    		--	   field mentions all the things used by the segment
    		--	   that are bound after their use
    	    segs_w_fwd_refs          = addFwdRefs segs

    		-- Step 3: Group together the segments to make bigger segments
    		--	   Invariant: in the result, no segment uses a variable
    		--	   	      bound in a later segment
    	    grouped_segs = glomSegments segs_w_fwd_refs

    		-- Step 4: Turn the segments into Stmts
    		--	   Use RecStmt when and only when there are fwd refs
    		--	   Also gather up the uses from the end towards the
    		--	   start, so we can tell the RecStmt which things are
    		--	   used 'after' the RecStmt
    	    empty_rec_stmt = emptyRecStmt { recS_ret_fn  = return_op
                                              , recS_mfix_fn = mfix_op
                                              , recS_bind_fn = bind_op }
    	    (rec_stmts', fvs) = segsToStmts empty_rec_stmt grouped_segs fvs_later

    	; return ((rec_stmts', thing), fvs `plusFV` fvs1 `plusFV` fvs2 `plusFV` fvs3) } }

    rnStmt ctxt (L loc (ParStmt segs)) thing_inside
      = do	{ checkParStmt ctxt
    	; ((segs', thing), fvs) <- rnParallelStmts (ParStmtCtxt ctxt) segs thing_inside
    	; return (([L loc (ParStmt segs')], thing), fvs) }

    rnStmt ctxt (L loc (TransformStmt stmts _ using by)) thing_inside
      = do { checkTransformStmt ctxt

           ; (using', fvs1) <- rnLExpr using

           ; ((stmts', (by', used_bndrs, thing)), fvs2)
                 <- rnNormalStmts (TransformStmtCtxt ctxt) stmts $ \ bndrs ->
                    do { (by', fvs_by) <- case by of
                                            Nothing -> return (Nothing, emptyFVs)
                                            Just e  -> do { (e', fvs) <- rnLExpr e; return (Just e', fvs) }
                       ; (thing, fvs_thing) <- thing_inside bndrs
                       ; let fvs        = fvs_by `plusFV` fvs_thing
                             used_bndrs = filter (`elemNameSet` fvs) bndrs
                             -- The paper (Fig 5) has a bug here; we must treat any free varaible of
                             -- the "thing inside", **or of the by-expression**, as used
                       ; return ((by', used_bndrs, thing), fvs) }

           ; return (([L loc (TransformStmt stmts' used_bndrs using' by')], thing),
                     fvs1 `plusFV` fvs2) }

    rnStmt ctxt (L loc (GroupStmt stmts _ by using)) thing_inside
      = do { checkTransformStmt ctxt

             -- Rename the 'using' expression in the context before the transform is begun
           ; (using', fvs1) <- case using of
                                 Left e  -> do { (e', fvs) <- rnLExpr e; return (Left e', fvs) }
    			     Right _ -> do { (e', fvs) <- lookupSyntaxName groupWithName
                                               ; return (Right e', fvs) }

             -- Rename the stmts and the 'by' expression
    	 -- Keep track of the variables mentioned in the 'by' expression
           ; ((stmts', (by', used_bndrs, thing)), fvs2)
                 <- rnNormalStmts (TransformStmtCtxt ctxt) stmts $ \ bndrs ->
                    do { (by',   fvs_by) <- mapMaybeFvRn rnLExpr by
                       ; (thing, fvs_thing) <- thing_inside bndrs
                       ; let fvs = fvs_by `plusFV` fvs_thing
                             used_bndrs = filter (`elemNameSet` fvs) bndrs
                       ; return ((by', used_bndrs, thing), fvs) }

           ; let all_fvs  = fvs1 `plusFV` fvs2
                 bndr_map = used_bndrs `zip` used_bndrs
    	     -- See Note [GroupStmt binder map] in HsExpr

           ; traceRn (text "rnStmt: implicitly rebound these used binders:" <+> ppr bndr_map)
           ; return (([L loc (GroupStmt stmts' bndr_map by' using')], thing), all_fvs) }

    type ParSeg id = ([LStmt id], [id])	   -- The Names are bound by the Stmts

    rnParallelStmts :: forall thing. HsStmtContext Name
                    -> [ParSeg RdrName]
                    -> ([Name] -> RnM (thing, FreeVars))
                    -> RnM (([ParSeg Name], thing), FreeVars)
    -- Note [Renaming parallel Stmts]
    rnParallelStmts ctxt segs thing_inside
      = do { orig_lcl_env <- getLocalRdrEnv
           ; rn_segs orig_lcl_env [] segs }
      where
        rn_segs :: LocalRdrEnv
                -> [Name] -> [ParSeg RdrName]
                -> RnM (([ParSeg Name], thing), FreeVars)
        rn_segs _ bndrs_so_far []
          = do { let (bndrs', dups) = removeDups cmpByOcc bndrs_so_far
               ; mapM_ dupErr dups
               ; (thing, fvs) <- bindLocalNames bndrs' (thing_inside bndrs')
               ; return (([], thing), fvs) }

        rn_segs env bndrs_so_far ((stmts,_) : segs)
          = do { ((stmts', (used_bndrs, segs', thing)), fvs)
                        <- rnNormalStmts ctxt stmts $ \ bndrs ->
                           setLocalRdrEnv env       $ do
                           { ((segs', thing), fvs) <- rn_segs env (bndrs ++ bndrs_so_far) segs
    		       ; let used_bndrs = filter (`elemNameSet` fvs) bndrs
                           ; return ((used_bndrs, segs', thing), fvs) }

               ; let seg' = (stmts', used_bndrs)
               ; return ((seg':segs', thing), fvs) }

        cmpByOcc n1 n2 = nameOccName n1 `compare` nameOccName n2
        dupErr vs = addErr (ptext (sLit "Duplicate binding in parallel list comprehension for:")
                        <+> quotes (ppr (head vs)))

\end{code} Note [Renaming parallel Stmts] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Renaming parallel statements is painful. Given, say [ a+c | a <- as, bs <- bss | c <- bs, a <- ds ] Note that (a) In order to report "Defined by not used" about 'bs', we must rename each group of Stmts with a thing_inside whose FreeVars include at least {a,c} (b) We want to report that 'a' is illegally bound in both branches (c) The 'bs' in the second group must obviously not be captured by the binding in the first group To satisfy (a) we nest the segements. To satisfy (b) we check for duplicates just before thing_inside. To satisfy (c) we reset the LocalRdrEnv each time. %************************************************************************ %* * \subsubsection{mdo expressions} %* * %************************************************************************ \begin{code}

    type FwdRefs = NameSet
    type Segment stmts = (Defs,
    		      Uses, 	-- May include defs
    		      FwdRefs,	-- A subset of uses that are
    				--   (a) used before they are bound in this segment, or
    				--   (b) used here, and bound in subsequent segments
    		      stmts)	-- Either Stmt or [Stmt]

    ----------------------------------------------------

    rnMDoStmts :: [LStmt RdrName]
    	   -> RnM (thing, FreeVars)
    	   -> RnM (([LStmt Name], thing), FreeVars)
    rnMDoStmts stmts thing_inside
      = rn_rec_stmts_and_then stmts $ \ segs -> do
        { (thing, fvs_later) <- thing_inside
        ; let   segs_w_fwd_refs = addFwdRefs segs
    	    grouped_segs = glomSegments segs_w_fwd_refs
    	    (stmts', fvs) = segsToStmts emptyRecStmt grouped_segs fvs_later
        ; return ((stmts', thing), fvs) }

    ---------------------------------------------

    -- wrapper that does both the left- and right-hand sides
    rn_rec_stmts_and_then :: [LStmt RdrName]
                             -- assumes that the FreeVars returned includes
                             -- the FreeVars of the Segments
                          -> ([Segment (LStmt Name)] -> RnM (a, FreeVars))
                          -> RnM (a, FreeVars)
    rn_rec_stmts_and_then s cont
      = do	{ -- (A) Make the mini fixity env for all of the stmts
    	  fix_env <- makeMiniFixityEnv (collectRecStmtsFixities s)

    	  -- (B) Do the LHSes
    	; new_lhs_and_fv <- rn_rec_stmts_lhs fix_env s

    	  --    ...bring them and their fixities into scope
    	; let bound_names = collectLStmtsBinders (map fst new_lhs_and_fv)
    	; bindLocalNamesFV bound_names $
              addLocalFixities fix_env bound_names $ do

    	  -- (C) do the right-hand-sides and thing-inside
    	{ segs <- rn_rec_stmts bound_names new_lhs_and_fv
    	; (res, fvs) <- cont segs
    	; warnUnusedLocalBinds bound_names fvs
    	; return (res, fvs) }}

    -- get all the fixity decls in any Let stmt
    collectRecStmtsFixities :: [LStmtLR RdrName RdrName] -> [LFixitySig RdrName]
    collectRecStmtsFixities l =
        foldr (\ s -> \acc -> case s of
                                (L _ (LetStmt (HsValBinds (ValBindsIn _ sigs)))) ->
                                    foldr (\ sig -> \ acc -> case sig of
                                                               (L loc (FixSig s)) -> (L loc s) : acc
                                                               _ -> acc) acc sigs
                                _ -> acc) [] l

    -- left-hand sides

    rn_rec_stmt_lhs :: MiniFixityEnv
                    -> LStmt RdrName
                       -- rename LHS, and return its FVs
                       -- Warning: we will only need the FreeVars below in the case of a BindStmt,
                       -- so we don't bother to compute it accurately in the other cases
                    -> RnM [(LStmtLR Name RdrName, FreeVars)]

    rn_rec_stmt_lhs _ (L loc (ExprStmt expr a b)) = return [(L loc (ExprStmt expr a b),
                                                           -- this is actually correct
                                                           emptyFVs)]

    rn_rec_stmt_lhs fix_env (L loc (BindStmt pat expr a b))
      = do
          -- should the ctxt be MDo instead?
          (pat', fv_pat) <- rnBindPat (localRecNameMaker fix_env) pat
          return [(L loc (BindStmt pat' expr a b),
                   fv_pat)]

    rn_rec_stmt_lhs _ (L _ (LetStmt binds@(HsIPBinds _)))
      = failWith (badIpBinds (ptext (sLit "an mdo expression")) binds)

    rn_rec_stmt_lhs fix_env (L loc (LetStmt (HsValBinds binds)))
        = do (_bound_names, binds') <- rnLocalValBindsLHS fix_env binds
             return [(L loc (LetStmt (HsValBinds binds')),
                     -- Warning: this is bogus; see function invariant
                     emptyFVs
                     )]

    -- XXX Do we need to do something with the return and mfix names?
    rn_rec_stmt_lhs fix_env (L _ (RecStmt { recS_stmts = stmts }))	-- Flatten Rec inside Rec
        = rn_rec_stmts_lhs fix_env stmts

    rn_rec_stmt_lhs _ stmt@(L _ (ParStmt _))	-- Syntactically illegal in mdo
      = pprPanic "rn_rec_stmt" (ppr stmt)

    rn_rec_stmt_lhs _ stmt@(L _ (TransformStmt {}))	-- Syntactically illegal in mdo
      = pprPanic "rn_rec_stmt" (ppr stmt)

    rn_rec_stmt_lhs _ stmt@(L _ (GroupStmt {}))	-- Syntactically illegal in mdo
      = pprPanic "rn_rec_stmt" (ppr stmt)

    rn_rec_stmt_lhs _ (L _ (LetStmt EmptyLocalBinds))
      = panic "rn_rec_stmt LetStmt EmptyLocalBinds"

    rn_rec_stmts_lhs :: MiniFixityEnv
                     -> [LStmt RdrName]
                     -> RnM [(LStmtLR Name RdrName, FreeVars)]
    rn_rec_stmts_lhs fix_env stmts
      = do { ls <- concatMapM (rn_rec_stmt_lhs fix_env) stmts
           ; let boundNames = collectLStmtsBinders (map fst ls)
                -- First do error checking: we need to check for dups here because we
                -- don't bind all of the variables from the Stmt at once
                -- with bindLocatedLocals.
           ; checkDupNames boundNames
           ; return ls }

    -- right-hand-sides

    rn_rec_stmt :: [Name] -> LStmtLR Name RdrName -> FreeVars -> RnM [Segment (LStmt Name)]
    	-- Rename a Stmt that is inside a RecStmt (or mdo)
    	-- Assumes all binders are already in scope
    	-- Turns each stmt into a singleton Stmt
    rn_rec_stmt _ (L loc (ExprStmt expr _ _)) _
      = rnLExpr expr `thenM` \ (expr', fvs) ->
        lookupSyntaxName thenMName	`thenM` \ (then_op, fvs1) ->
        return [(emptyNameSet, fvs `plusFV` fvs1, emptyNameSet,
    	      L loc (ExprStmt expr' then_op placeHolderType))]

    rn_rec_stmt _ (L loc (BindStmt pat' expr _ _)) fv_pat
      = rnLExpr expr		`thenM` \ (expr', fv_expr) ->
        lookupSyntaxName bindMName	`thenM` \ (bind_op, fvs1) ->
        lookupSyntaxName failMName	`thenM` \ (fail_op, fvs2) ->
        let
    	bndrs = mkNameSet (collectPatBinders pat')
    	fvs   = fv_expr `plusFV` fv_pat `plusFV` fvs1 `plusFV` fvs2
        in
        return [(bndrs, fvs, bndrs `intersectNameSet` fvs,
    	      L loc (BindStmt pat' expr' bind_op fail_op))]

    rn_rec_stmt _ (L _ (LetStmt binds@(HsIPBinds _))) _
      = failWith (badIpBinds (ptext (sLit "an mdo expression")) binds)

    rn_rec_stmt all_bndrs (L loc (LetStmt (HsValBinds binds'))) _ = do
      (binds', du_binds) <-
          -- fixities and unused are handled above in rn_rec_stmts_and_then
          rnLocalValBindsRHS (mkNameSet all_bndrs) binds'
      return [(duDefs du_binds, allUses du_binds,
    	   emptyNameSet, L loc (LetStmt (HsValBinds binds')))]

    -- no RecStmt case becuase they get flattened above when doing the LHSes
    rn_rec_stmt _ stmt@(L _ (RecStmt {})) _
      = pprPanic "rn_rec_stmt: RecStmt" (ppr stmt)

    rn_rec_stmt _ stmt@(L _ (ParStmt {})) _	-- Syntactically illegal in mdo
      = pprPanic "rn_rec_stmt: ParStmt" (ppr stmt)

    rn_rec_stmt _ stmt@(L _ (TransformStmt {})) _	-- Syntactically illegal in mdo
      = pprPanic "rn_rec_stmt: TransformStmt" (ppr stmt)

    rn_rec_stmt _ stmt@(L _ (GroupStmt {})) _	-- Syntactically illegal in mdo
      = pprPanic "rn_rec_stmt: GroupStmt" (ppr stmt)

    rn_rec_stmt _ (L _ (LetStmt EmptyLocalBinds)) _
      = panic "rn_rec_stmt: LetStmt EmptyLocalBinds"

    rn_rec_stmts :: [Name] -> [(LStmtLR Name RdrName, FreeVars)] -> RnM [Segment (LStmt Name)]
    rn_rec_stmts bndrs stmts = mapM (uncurry (rn_rec_stmt bndrs)) stmts	`thenM` \ segs_s ->
    		   	   return (concat segs_s)

    ---------------------------------------------
    addFwdRefs :: [Segment a] -> [Segment a]
    -- So far the segments only have forward refs *within* the Stmt
    -- 	(which happens for bind:  x <- ...x...)
    -- This function adds the cross-seg fwd ref info

    addFwdRefs pairs
      = fst (foldr mk_seg ([], emptyNameSet) pairs)
      where
        mk_seg (defs, uses, fwds, stmts) (segs, later_defs)
    	= (new_seg : segs, all_defs)
    	where
    	  new_seg = (defs, uses, new_fwds, stmts)
    	  all_defs = later_defs `unionNameSets` defs
    	  new_fwds = fwds `unionNameSets` (uses `intersectNameSet` later_defs)
    		-- Add the downstream fwd refs here

    ----------------------------------------------------
    -- 	Glomming the singleton segments of an mdo into
    --	minimal recursive groups.
    --
    -- At first I thought this was just strongly connected components, but
    -- there's an important constraint: the order of the stmts must not change.
    --
    -- Consider
    --	mdo { x <- ...y...
    --	      p <- z
    --	      y <- ...x...
    --	      q <- x
    --	      z <- y
    --	      r <- x }
    --
    -- Here, the first stmt mention 'y', which is bound in the third.
    -- But that means that the innocent second stmt (p <- z) gets caught
    -- up in the recursion.  And that in turn means that the binding for
    -- 'z' has to be included... and so on.
    --
    -- Start at the tail { r <- x }
    -- Now add the next one { z <- y ; r <- x }
    -- Now add one more     { q <- x ; z <- y ; r <- x }
    -- Now one more... but this time we have to group a bunch into rec
    --	{ rec { y <- ...x... ; q <- x ; z <- y } ; r <- x }
    -- Now one more, which we can add on without a rec
    --	{ p <- z ;
    --	  rec { y <- ...x... ; q <- x ; z <- y } ;
    -- 	  r <- x }
    -- Finally we add the last one; since it mentions y we have to
    -- glom it togeher with the first two groups
    --	{ rec { x <- ...y...; p <- z ; y <- ...x... ;
    --		q <- x ; z <- y } ;
    -- 	  r <- x }

    glomSegments :: [Segment (LStmt Name)] -> [Segment [LStmt Name]]

    glomSegments [] = []
    glomSegments ((defs,uses,fwds,stmt) : segs)
    	-- Actually stmts will always be a singleton
      = (seg_defs, seg_uses, seg_fwds, seg_stmts)  : others
      where
        segs'	     = glomSegments segs
        (extras, others) = grab uses segs'
        (ds, us, fs, ss) = unzip4 extras

        seg_defs  = plusFVs ds `plusFV` defs
        seg_uses  = plusFVs us `plusFV` uses
        seg_fwds  = plusFVs fs `plusFV` fwds
        seg_stmts = stmt : concat ss

        grab :: NameSet	 	-- The client
    	 -> [Segment a]
    	 -> ([Segment a],	-- Needed by the 'client'
    	     [Segment a])	-- Not needed by the client
    	-- The result is simply a split of the input
        grab uses dus
    	= (reverse yeses, reverse noes)
    	where
    	  (noes, yeses) 	  = span not_needed (reverse dus)
    	  not_needed (defs,_,_,_) = not (intersectsNameSet defs uses)

    ----------------------------------------------------
    segsToStmts :: Stmt Name		-- A RecStmt with the SyntaxOps filled in
                -> [Segment [LStmt Name]]
    	    -> FreeVars			-- Free vars used 'later'
    	    -> ([LStmt Name], FreeVars)

    segsToStmts _ [] fvs_later = ([], fvs_later)
    segsToStmts empty_rec_stmt ((defs, uses, fwds, ss) : segs) fvs_later
      = ASSERT( not (null ss) )
        (new_stmt : later_stmts, later_uses `plusFV` uses)
      where
        (later_stmts, later_uses) = segsToStmts empty_rec_stmt segs fvs_later
        new_stmt | non_rec	 = head ss
    	     | otherwise = L (getLoc (head ss)) rec_stmt
        rec_stmt = empty_rec_stmt { recS_stmts     = ss
                                  , recS_later_ids = nameSetToList used_later
                                  , recS_rec_ids   = nameSetToList fwds }
        non_rec    = isSingleton ss && isEmptyNameSet fwds
        used_later = defs `intersectNameSet` later_uses
    				-- The ones needed after the RecStmt

\end{code} %************************************************************************ %* * \subsubsection{Assertion utils} %* * %************************************************************************ \begin{code}

    srcSpanPrimLit :: SrcSpan -> HsExpr Name
    srcSpanPrimLit span = HsLit (HsStringPrim (mkFastString (showSDocOneLine (ppr span))))

    mkAssertErrorExpr :: RnM (HsExpr Name)
    -- Return an expression for (assertError "Foo.hs:27")
    mkAssertErrorExpr
      = getSrcSpanM    			`thenM` \ sloc ->
        return (HsApp (L sloc (HsVar assertErrorName))
    		  (L sloc (srcSpanPrimLit sloc)))

\end{code} Note [Adding the implicit parameter to 'assert'] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The renamer transforms (assert e1 e2) to (assert "Foo.hs:27" e1 e2). By doing this in the renamer we allow the typechecker to just see the expanded application and do the right thing. But it's not really the Right Thing because there's no way to "undo" if you want to see the original source code. We'll have fix this in due course, when we care more about being able to reconstruct the exact original program. %************************************************************************ %* * \subsubsection{Errors} %* * %************************************************************************ \begin{code}

    ----------------------
    -- Checking when a particular Stmt is ok
    checkLetStmt :: HsStmtContext Name -> HsLocalBinds RdrName -> RnM ()
    checkLetStmt (ParStmtCtxt _) (HsIPBinds binds) = addErr (badIpBinds (ptext (sLit "a parallel list comprehension:")) binds)
    checkLetStmt _ctxt 	     _binds	       = return ()
      	-- We do not allow implicit-parameter bindings in a parallel
    	-- list comprehension.  I'm not sure what it might mean.

    ---------
    checkRecStmt :: HsStmtContext Name -> RnM ()
    checkRecStmt (MDoExpr {}) = return ()	-- Recursive stmt ok in 'mdo'
    checkRecStmt (DoExpr {})  = return ()	-- and in 'do'
    checkRecStmt ctxt	  = addErr msg
      where
        msg = ptext (sLit "Illegal 'rec' stmt in") <+> pprStmtContext ctxt

    ---------
    checkParStmt :: HsStmtContext Name -> RnM ()
    checkParStmt _
      = do	{ parallel_list_comp <- xoptM Opt_ParallelListComp
    	; checkErr parallel_list_comp msg }
      where
        msg = ptext (sLit "Illegal parallel list comprehension: use -XParallelListComp")

    ---------
    checkTransformStmt :: HsStmtContext Name -> RnM ()
    checkTransformStmt ListComp  -- Ensure we are really within a list comprehension because otherwise the
    			     -- desugarer will break when we come to operate on a parallel array
      = do	{ transform_list_comp <- xoptM Opt_TransformListComp
    	; checkErr transform_list_comp msg }
      where
        msg = ptext (sLit "Illegal transform or grouping list comprehension: use -XTransformListComp")
    checkTransformStmt (ParStmtCtxt       ctxt) = checkTransformStmt ctxt	-- Ok to nest inside a parallel comprehension
    checkTransformStmt (TransformStmtCtxt ctxt) = checkTransformStmt ctxt	-- Ok to nest inside a parallel comprehension
    checkTransformStmt ctxt = addErr msg
      where
        msg = ptext (sLit "Illegal transform or grouping in") <+> pprStmtContext ctxt

    ---------
    checkTupleSection :: [HsTupArg RdrName] -> RnM ()
    checkTupleSection args
      = do	{ tuple_section <- xoptM Opt_TupleSections
    	; checkErr (all tupArgPresent args || tuple_section) msg }
      where
        msg = ptext (sLit "Illegal tuple section: use -XTupleSections")

    ---------
    sectionErr :: HsExpr RdrName -> SDoc
    sectionErr expr
      = hang (ptext (sLit "A section must be enclosed in parentheses"))
           2 (ptext (sLit "thus:") <+> (parens (ppr expr)))

    patSynErr :: HsExpr RdrName -> RnM (HsExpr Name, FreeVars)
    patSynErr e = do { addErr (sep [ptext (sLit "Pattern syntax in expression context:"),
    			 	nest 4 (ppr e)])
    		 ; return (EWildPat, emptyFVs) }

    badIpBinds :: Outputable a => SDoc -> a -> SDoc
    badIpBinds what binds
      = hang (ptext (sLit "Implicit-parameter bindings illegal in") <+> what)
    	 2 (ppr binds)

\end{code}