hsSyn/HsUtils.hs

    {-
    (c) The University of Glasgow, 1992-2006

    Here we collect a variety of helper functions that construct or
    analyse HsSyn.  All these functions deal with generic HsSyn; functions
    which deal with the instantiated versions are located elsewhere:

       Parameterised by     Module
       ----------------     -------------
       RdrName              parser/RdrHsSyn
       Name                 rename/RnHsSyn
       Id                   typecheck/TcHsSyn
    -}

    {-# LANGUAGE CPP #-}
    {-# LANGUAGE ScopedTypeVariables #-}
    {-# LANGUAGE FlexibleContexts #-}

    module HsUtils(
      -- Terms
      mkHsPar, mkHsApp, mkHsConApp, mkSimpleHsAlt,
      mkSimpleMatch, unguardedGRHSs, unguardedRHS,
      mkMatchGroup, mkMatchGroupName, mkMatch, mkHsLam, mkHsIf,
      mkHsWrap, mkLHsWrap, mkHsWrapCo, mkHsWrapCoR, mkLHsWrapCo,
      coToHsWrapper, mkHsDictLet, mkHsLams,
      mkHsOpApp, mkHsDo, mkHsComp, mkHsWrapPat, mkHsWrapPatCo,
      mkLHsPar, mkHsCmdCast,

      nlHsTyApp, nlHsTyApps, nlHsVar, nlHsLit, nlHsApp, nlHsApps, nlHsIntLit, nlHsVarApps,
      nlHsDo, nlHsOpApp, nlHsLam, nlHsPar, nlHsIf, nlHsCase, nlList,
      mkLHsTupleExpr, mkLHsVarTuple, missingTupArg,
      toHsType, toHsKind,

      -- Bindings
      mkFunBind, mkVarBind, mkHsVarBind, mk_easy_FunBind, mkTopFunBind, mkPatSynBind,

      -- Literals
      mkHsIntegral, mkHsFractional, mkHsIsString, mkHsString,

      -- Patterns
      mkNPat, mkNPlusKPat, nlVarPat, nlLitPat, nlConVarPat, nlConPat,
      nlConPatName, nlInfixConPat, nlNullaryConPat, nlWildConPat, nlWildPat,
      nlWildPatName, nlWildPatId, nlTuplePat, mkParPat,

      -- Types
      mkHsAppTy, userHsTyVarBndrs,
      nlHsAppTy, nlHsTyVar, nlHsFunTy, nlHsTyConApp,

      -- Stmts
      mkTransformStmt, mkTransformByStmt, mkBodyStmt, mkBindStmt, mkLastStmt,
      emptyTransStmt, mkGroupUsingStmt, mkGroupByUsingStmt,
      emptyRecStmt, emptyRecStmtName, emptyRecStmtId, mkRecStmt,

      -- Template Haskell
      mkHsSpliceTy, mkHsSpliceE, mkHsSpliceTE, mkHsSplice,
      mkHsQuasiQuote, unqualQuasiQuote,

      -- Flags
      noRebindableInfo,

      -- Collecting binders
      collectLocalBinders, collectHsValBinders, collectHsBindListBinders,
      collectHsIdBinders,
      collectHsBindsBinders, collectHsBindBinders, collectMethodBinders,
      collectPatBinders, collectPatsBinders,
      collectLStmtsBinders, collectStmtsBinders,
      collectLStmtBinders, collectStmtBinders,

      hsLTyClDeclBinders, hsTyClForeignBinders, hsPatSynBinders,
      hsForeignDeclsBinders, hsGroupBinders, hsDataFamInstBinders,

      -- Collecting implicit binders
      lStmtsImplicits, hsValBindsImplicits, lPatImplicits
      ) where

    #include "HsVersions.h"

    import HsDecls
    import HsBinds
    import HsExpr
    import HsPat
    import HsTypes
    import HsLit
    import PlaceHolder

    import TcEvidence
    import RdrName
    import Var
    import TypeRep
    import TcType
    import Kind
    import DataCon
    import Name
    import NameSet
    import BasicTypes
    import SrcLoc
    import FastString
    import Util
    import Bag
    import Outputable

    import Data.Either
    import Data.Function
    import Data.List

    {-
    ************************************************************************
    *                                                                      *
            Some useful helpers for constructing syntax
    *                                                                      *
    ************************************************************************

    These functions attempt to construct a not-completely-useless SrcSpan
    from their components, compared with the nl* functions below which
    just attach noSrcSpan to everything.
    -}

    mkHsPar :: LHsExpr id -> LHsExpr id
    mkHsPar e = L (getLoc e) (HsPar e)

    mkSimpleMatch :: [LPat id] -> Located (body id) -> LMatch id (Located (body id))
    mkSimpleMatch pats rhs
      = L loc $
        Match Nothing pats Nothing (unguardedGRHSs rhs)
      where
        loc = case pats of
                    []      -> getLoc rhs
                    (pat:_) -> combineSrcSpans (getLoc pat) (getLoc rhs)

    unguardedGRHSs :: Located (body id) -> GRHSs id (Located (body id))
    unguardedGRHSs rhs@(L loc _) = GRHSs (unguardedRHS loc rhs) emptyLocalBinds

    unguardedRHS :: SrcSpan -> Located (body id) -> [LGRHS id (Located (body id))]
    unguardedRHS loc rhs = [L loc (GRHS [] rhs)]

    mkMatchGroup :: Origin -> [LMatch RdrName (Located (body RdrName))]
                 -> MatchGroup RdrName (Located (body RdrName))
    mkMatchGroup origin matches = MG { mg_alts = matches, mg_arg_tys = []
                                     , mg_res_ty = placeHolderType
                                     , mg_origin = origin }

    mkMatchGroupName :: Origin -> [LMatch Name (Located (body Name))]
                 -> MatchGroup Name (Located (body Name))
    mkMatchGroupName origin matches = MG { mg_alts = matches, mg_arg_tys = []
                                         , mg_res_ty = placeHolderType
                                         , mg_origin = origin }

    mkHsAppTy :: LHsType name -> LHsType name -> LHsType name
    mkHsAppTy t1 t2 = addCLoc t1 t2 (HsAppTy t1 t2)

    mkHsApp :: LHsExpr name -> LHsExpr name -> LHsExpr name
    mkHsApp e1 e2 = addCLoc e1 e2 (HsApp e1 e2)

    mkHsLam :: [LPat RdrName] -> LHsExpr RdrName -> LHsExpr RdrName
    mkHsLam pats body = mkHsPar (L (getLoc body) (HsLam matches))
            where
              matches = mkMatchGroup Generated [mkSimpleMatch pats body]

    mkHsLams :: [TyVar] -> [EvVar] -> LHsExpr Id -> LHsExpr Id
    mkHsLams tyvars dicts expr = mkLHsWrap (mkWpTyLams tyvars
                                           <.> mkWpLams dicts) expr

    mkHsConApp :: DataCon -> [Type] -> [HsExpr Id] -> LHsExpr Id
    -- Used for constructing dictionary terms etc, so no locations
    mkHsConApp data_con tys args
      = foldl mk_app (nlHsTyApp (dataConWrapId data_con) tys) args
      where
        mk_app f a = noLoc (HsApp f (noLoc a))

    mkSimpleHsAlt :: LPat id -> (Located (body id)) -> LMatch id (Located (body id))
    -- A simple lambda with a single pattern, no binds, no guards; pre-typechecking
    mkSimpleHsAlt pat expr
      = mkSimpleMatch [pat] expr

    nlHsTyApp :: name -> [Type] -> LHsExpr name
    nlHsTyApp fun_id tys = noLoc (HsWrap (mkWpTyApps tys) (HsVar fun_id))

    nlHsTyApps :: name -> [Type] -> [LHsExpr name] -> LHsExpr name
    nlHsTyApps fun_id tys xs = foldl nlHsApp (nlHsTyApp fun_id tys) xs

    --------- Adding parens ---------
    mkLHsPar :: LHsExpr name -> LHsExpr name
    -- Wrap in parens if hsExprNeedsParens says it needs them
    -- So   'f x'  becomes '(f x)', but '3' stays as '3'
    mkLHsPar le@(L loc e) | hsExprNeedsParens e = L loc (HsPar le)
                          | otherwise           = le

    mkParPat :: LPat name -> LPat name
    mkParPat lp@(L loc p) | hsPatNeedsParens p = L loc (ParPat lp)
                          | otherwise          = lp

    -------------------------------
    -- These are the bits of syntax that contain rebindable names
    -- See RnEnv.lookupSyntaxName

    mkHsIntegral   :: String -> Integer -> PostTc RdrName Type -> HsOverLit RdrName
    mkHsFractional :: FractionalLit -> PostTc RdrName Type -> HsOverLit RdrName
    mkHsIsString :: String -> FastString -> PostTc RdrName Type -> HsOverLit RdrName
    mkHsDo         :: HsStmtContext Name -> [ExprLStmt RdrName] -> HsExpr RdrName
    mkHsComp       :: HsStmtContext Name -> [ExprLStmt RdrName] -> LHsExpr RdrName
                   -> HsExpr RdrName

    mkNPat      :: Located (HsOverLit id) -> Maybe (SyntaxExpr id) -> Pat id
    mkNPlusKPat :: Located id -> Located (HsOverLit id) -> Pat id

    mkLastStmt :: Located (bodyR idR) -> StmtLR idL idR (Located (bodyR idR))
    mkBodyStmt :: Located (bodyR RdrName)
               -> StmtLR idL RdrName (Located (bodyR RdrName))
    mkBindStmt :: LPat idL -> Located (bodyR idR) -> StmtLR idL idR (Located (bodyR idR))

    emptyRecStmt     :: StmtLR idL  RdrName bodyR
    emptyRecStmtName :: StmtLR Name Name    bodyR
    emptyRecStmtId   :: StmtLR Id   Id      bodyR
    mkRecStmt    :: [LStmtLR idL RdrName bodyR] -> StmtLR idL RdrName bodyR

    mkHsIntegral src i  = OverLit (HsIntegral   src i) noRebindableInfo noSyntaxExpr
    mkHsFractional   f  = OverLit (HsFractional     f) noRebindableInfo noSyntaxExpr
    mkHsIsString src s  = OverLit (HsIsString   src s) noRebindableInfo noSyntaxExpr

    noRebindableInfo :: PlaceHolder
    noRebindableInfo = PlaceHolder -- Just another placeholder;

    mkHsDo ctxt stmts = HsDo ctxt stmts placeHolderType
    mkHsComp ctxt stmts expr = mkHsDo ctxt (stmts ++ [last_stmt])
      where
        last_stmt = L (getLoc expr) $ mkLastStmt expr

    mkHsIf :: LHsExpr id -> LHsExpr id -> LHsExpr id -> HsExpr id
    mkHsIf c a b = HsIf (Just noSyntaxExpr) c a b

    mkNPat lit neg     = NPat lit neg noSyntaxExpr
    mkNPlusKPat id lit = NPlusKPat id lit noSyntaxExpr noSyntaxExpr

    mkTransformStmt    :: [ExprLStmt idL] -> LHsExpr idR
                       -> StmtLR idL idR (LHsExpr idL)
    mkTransformByStmt  :: [ExprLStmt idL] -> LHsExpr idR -> LHsExpr idR
                       -> StmtLR idL idR (LHsExpr idL)
    mkGroupUsingStmt   :: [ExprLStmt idL]                -> LHsExpr idR
                       -> StmtLR idL idR (LHsExpr idL)
    mkGroupByUsingStmt :: [ExprLStmt idL] -> LHsExpr idR -> LHsExpr idR
                       -> StmtLR idL idR (LHsExpr idL)

    emptyTransStmt :: StmtLR idL idR (LHsExpr idR)
    emptyTransStmt = TransStmt { trS_form = panic "emptyTransStmt: form"
                               , trS_stmts = [], trS_bndrs = []
                               , trS_by = Nothing, trS_using = noLoc noSyntaxExpr
                               , trS_ret = noSyntaxExpr, trS_bind = noSyntaxExpr
                               , trS_fmap = noSyntaxExpr }
    mkTransformStmt    ss u   = emptyTransStmt { trS_form = ThenForm,  trS_stmts = ss, trS_using = u }
    mkTransformByStmt  ss u b = emptyTransStmt { trS_form = ThenForm,  trS_stmts = ss, trS_using = u, trS_by = Just b }
    mkGroupUsingStmt   ss u   = emptyTransStmt { trS_form = GroupForm, trS_stmts = ss, trS_using = u }
    mkGroupByUsingStmt ss b u = emptyTransStmt { trS_form = GroupForm, trS_stmts = ss, trS_using = u, trS_by = Just b }

    mkLastStmt body     = LastStmt body noSyntaxExpr
    mkBodyStmt body     = BodyStmt body noSyntaxExpr noSyntaxExpr placeHolderType
    mkBindStmt pat body = BindStmt pat body noSyntaxExpr noSyntaxExpr

    emptyRecStmt' :: forall idL idR body.
                           PostTc idR Type -> StmtLR idL idR body
    emptyRecStmt' tyVal =
       RecStmt
         { recS_stmts = [], recS_later_ids = []
         , recS_rec_ids = []
         , recS_ret_fn = noSyntaxExpr
         , recS_mfix_fn = noSyntaxExpr
         , recS_bind_fn = noSyntaxExpr, recS_later_rets = []
         , recS_rec_rets = [], recS_ret_ty = tyVal }

    emptyRecStmt     = emptyRecStmt' placeHolderType
    emptyRecStmtName = emptyRecStmt' placeHolderType
    emptyRecStmtId   = emptyRecStmt' placeHolderTypeTc
    mkRecStmt stmts  = emptyRecStmt { recS_stmts = stmts }

    -------------------------------
    --- A useful function for building @OpApps@.  The operator is always a
    -- variable, and we don't know the fixity yet.
    mkHsOpApp :: LHsExpr id -> id -> LHsExpr id -> HsExpr id
    mkHsOpApp e1 op e2 = OpApp e1 (noLoc (HsVar op)) (error "mkOpApp:fixity") e2

    mkHsSplice :: LHsExpr RdrName -> HsSplice RdrName
    mkHsSplice e = HsSplice unqualSplice e

    unqualSplice :: RdrName
    unqualSplice = mkRdrUnqual (mkVarOccFS (fsLit "splice"))

    mkHsSpliceE :: LHsExpr RdrName -> HsExpr RdrName
    mkHsSpliceE e = HsSpliceE False (mkHsSplice e)

    mkHsSpliceTE :: LHsExpr RdrName -> HsExpr RdrName
    mkHsSpliceTE e = HsSpliceE True (mkHsSplice e)

    mkHsSpliceTy :: LHsExpr RdrName -> HsType RdrName
    mkHsSpliceTy e = HsSpliceTy (mkHsSplice e) placeHolderKind

    mkHsQuasiQuote :: RdrName -> SrcSpan -> FastString -> HsQuasiQuote RdrName
    mkHsQuasiQuote quoter span quote = HsQuasiQuote quoter span quote

    unqualQuasiQuote :: RdrName
    unqualQuasiQuote = mkRdrUnqual (mkVarOccFS (fsLit "quasiquote"))
                    -- A name (uniquified later) to
                    -- identify the quasi-quote

    mkHsString :: String -> HsLit
    mkHsString s = HsString s (mkFastString s)

    -------------
    userHsTyVarBndrs :: SrcSpan -> [name] -> [Located (HsTyVarBndr name)]
    -- Caller sets location
    userHsTyVarBndrs loc bndrs = [ L loc (UserTyVar v) | v <- bndrs ]

    {-
    ************************************************************************
    *                                                                      *
            Constructing syntax with no location info
    *                                                                      *
    ************************************************************************
    -}

    nlHsVar :: id -> LHsExpr id
    nlHsVar n = noLoc (HsVar n)

    nlHsLit :: HsLit -> LHsExpr id
    nlHsLit n = noLoc (HsLit n)

    nlVarPat :: id -> LPat id
    nlVarPat n = noLoc (VarPat n)

    nlLitPat :: HsLit -> LPat id
    nlLitPat l = noLoc (LitPat l)

    nlHsApp :: LHsExpr id -> LHsExpr id -> LHsExpr id
    nlHsApp f x = noLoc (HsApp f x)

    nlHsIntLit :: Integer -> LHsExpr id
    nlHsIntLit n = noLoc (HsLit (HsInt (show n) n))

    nlHsApps :: id -> [LHsExpr id] -> LHsExpr id
    nlHsApps f xs = foldl nlHsApp (nlHsVar f) xs

    nlHsVarApps :: id -> [id] -> LHsExpr id
    nlHsVarApps f xs = noLoc (foldl mk (HsVar f) (map HsVar xs))
                     where
                       mk f a = HsApp (noLoc f) (noLoc a)

    nlConVarPat :: RdrName -> [RdrName] -> LPat RdrName
    nlConVarPat con vars = nlConPat con (map nlVarPat vars)

    nlInfixConPat :: id -> LPat id -> LPat id -> LPat id
    nlInfixConPat con l r = noLoc (ConPatIn (noLoc con) (InfixCon l r))

    nlConPat :: RdrName -> [LPat RdrName] -> LPat RdrName
    nlConPat con pats = noLoc (ConPatIn (noLoc con) (PrefixCon pats))

    nlConPatName :: Name -> [LPat Name] -> LPat Name
    nlConPatName con pats = noLoc (ConPatIn (noLoc con) (PrefixCon pats))

    nlNullaryConPat :: id -> LPat id
    nlNullaryConPat con = noLoc (ConPatIn (noLoc con) (PrefixCon []))

    nlWildConPat :: DataCon -> LPat RdrName
    nlWildConPat con = noLoc (ConPatIn (noLoc (getRdrName con))
                             (PrefixCon (nOfThem (dataConSourceArity con)
                                                 nlWildPat)))

    nlWildPat :: LPat RdrName
    nlWildPat  = noLoc (WildPat placeHolderType )  -- Pre-typechecking

    nlWildPatName :: LPat Name
    nlWildPatName  = noLoc (WildPat placeHolderType )  -- Pre-typechecking

    nlWildPatId :: LPat Id
    nlWildPatId  = noLoc (WildPat placeHolderTypeTc )  -- Post-typechecking

    nlHsDo :: HsStmtContext Name -> [LStmt RdrName (LHsExpr RdrName)]
           -> LHsExpr RdrName
    nlHsDo ctxt stmts = noLoc (mkHsDo ctxt stmts)

    nlHsOpApp :: LHsExpr id -> id -> LHsExpr id -> LHsExpr id
    nlHsOpApp e1 op e2 = noLoc (mkHsOpApp e1 op e2)

    nlHsLam  :: LMatch RdrName (LHsExpr RdrName) -> LHsExpr RdrName
    nlHsPar  :: LHsExpr id -> LHsExpr id
    nlHsIf   :: LHsExpr id -> LHsExpr id -> LHsExpr id -> LHsExpr id
    nlHsCase :: LHsExpr RdrName -> [LMatch RdrName (LHsExpr RdrName)]
             -> LHsExpr RdrName
    nlList   :: [LHsExpr RdrName] -> LHsExpr RdrName

    nlHsLam match          = noLoc (HsLam (mkMatchGroup Generated [match]))
    nlHsPar e              = noLoc (HsPar e)
    nlHsIf cond true false = noLoc (mkHsIf cond true false)
    nlHsCase expr matches  = noLoc (HsCase expr (mkMatchGroup Generated matches))
    nlList exprs           = noLoc (ExplicitList placeHolderType Nothing exprs)

    nlHsAppTy :: LHsType name -> LHsType name -> LHsType name
    nlHsTyVar :: name                         -> LHsType name
    nlHsFunTy :: LHsType name -> LHsType name -> LHsType name

    nlHsAppTy f t           = noLoc (HsAppTy f t)
    nlHsTyVar x             = noLoc (HsTyVar x)
    nlHsFunTy a b           = noLoc (HsFunTy a b)

    nlHsTyConApp :: name -> [LHsType name] -> LHsType name
    nlHsTyConApp tycon tys  = foldl nlHsAppTy (nlHsTyVar tycon) tys

    {-
    Tuples.  All these functions are *pre-typechecker* because they lack
    types on the tuple.
    -}

    mkLHsTupleExpr :: [LHsExpr a] -> LHsExpr a
    -- Makes a pre-typechecker boxed tuple, deals with 1 case
    mkLHsTupleExpr [e] = e
    mkLHsTupleExpr es  = noLoc $ ExplicitTuple (map (noLoc . Present) es) Boxed

    mkLHsVarTuple :: [a] -> LHsExpr a
    mkLHsVarTuple ids  = mkLHsTupleExpr (map nlHsVar ids)

    nlTuplePat :: [LPat id] -> Boxity -> LPat id
    nlTuplePat pats box = noLoc (TuplePat pats box [])

    missingTupArg :: HsTupArg RdrName
    missingTupArg = Missing placeHolderType

    {-
    ************************************************************************
    *                                                                      *
            Converting a Type to an HsType RdrName
    *                                                                      *
    ************************************************************************

    This is needed to implement GeneralizedNewtypeDeriving.
    -}

    toHsType :: Type -> LHsType RdrName
    toHsType ty
      | [] <- tvs_only
      , [] <- theta
      = to_hs_type tau
      | otherwise
      = noLoc $
        mkExplicitHsForAllTy (map mk_hs_tvb tvs_only)
                             (noLoc $ map toHsType theta)
                             (to_hs_type tau)

      where
        (tvs, theta, tau) = tcSplitSigmaTy ty
        tvs_only = filter isTypeVar tvs

        to_hs_type (TyVarTy tv) = nlHsTyVar (getRdrName tv)
        to_hs_type (AppTy t1 t2) = nlHsAppTy (toHsType t1) (toHsType t2)
        to_hs_type (TyConApp tc args) = nlHsTyConApp (getRdrName tc) (map toHsType args')
           where
             args' = filterOut isKind args
             -- Source-language types have _implicit_ kind arguments,
             -- so we must remove them here (Trac #8563)
        to_hs_type (FunTy arg res) = ASSERT( not (isConstraintKind (typeKind arg)) )
                                     nlHsFunTy (toHsType arg) (toHsType res)
        to_hs_type t@(ForAllTy {}) = pprPanic "toHsType" (ppr t)
        to_hs_type (LitTy (NumTyLit n)) = noLoc $ HsTyLit (HsNumTy "" n)
        to_hs_type (LitTy (StrTyLit s)) = noLoc $ HsTyLit (HsStrTy "" s)

        mk_hs_tvb tv = noLoc $ KindedTyVar (noLoc (getRdrName tv))
                                           (toHsKind (tyVarKind tv))

    toHsKind :: Kind -> LHsKind RdrName
    toHsKind = toHsType

    --------- HsWrappers: type args, dict args, casts ---------
    mkLHsWrap :: HsWrapper -> LHsExpr id -> LHsExpr id
    mkLHsWrap co_fn (L loc e) = L loc (mkHsWrap co_fn e)

    mkHsWrap :: HsWrapper -> HsExpr id -> HsExpr id
    mkHsWrap co_fn e | isIdHsWrapper co_fn = e
                     | otherwise           = HsWrap co_fn e

    mkHsWrapCo :: TcCoercion   -- A Nominal coercion  a ~N b
               -> HsExpr id -> HsExpr id
    mkHsWrapCo co e = mkHsWrap (coToHsWrapper co) e

    mkHsWrapCoR :: TcCoercion   -- A Representational coercion  a ~R b
                -> HsExpr id -> HsExpr id
    mkHsWrapCoR co e = mkHsWrap (coToHsWrapperR co) e

    mkLHsWrapCo :: TcCoercion -> LHsExpr id -> LHsExpr id
    mkLHsWrapCo co (L loc e) = L loc (mkHsWrapCo co e)

    mkHsCmdCast :: TcCoercion -> HsCmd id -> HsCmd id
    mkHsCmdCast co cmd | isTcReflCo co = cmd
                       | otherwise     = HsCmdCast co cmd

    coToHsWrapper :: TcCoercion -> HsWrapper   -- A Nominal coercion
    coToHsWrapper co | isTcReflCo co = idHsWrapper
                     | otherwise     = mkWpCast (mkTcSubCo co)

    coToHsWrapperR :: TcCoercion -> HsWrapper   -- A Representational coercion
    coToHsWrapperR co | isTcReflCo co = idHsWrapper
                      | otherwise     = mkWpCast co

    mkHsWrapPat :: HsWrapper -> Pat id -> Type -> Pat id
    mkHsWrapPat co_fn p ty | isIdHsWrapper co_fn = p
                           | otherwise           = CoPat co_fn p ty

    mkHsWrapPatCo :: TcCoercion -> Pat id -> Type -> Pat id
    mkHsWrapPatCo co pat ty | isTcReflCo co = pat
                            | otherwise     = CoPat (mkWpCast co) pat ty

    mkHsDictLet :: TcEvBinds -> LHsExpr Id -> LHsExpr Id
    mkHsDictLet ev_binds expr = mkLHsWrap (mkWpLet ev_binds) expr

    {-
    l
    ************************************************************************
    *                                                                      *
                    Bindings; with a location at the top
    *                                                                      *
    ************************************************************************
    -}

    mkFunBind :: Located RdrName -> [LMatch RdrName (LHsExpr RdrName)]
              -> HsBind RdrName
    -- Not infix, with place holders for coercion and free vars
    mkFunBind fn ms = FunBind { fun_id = fn, fun_infix = False
                              , fun_matches = mkMatchGroup Generated ms
                              , fun_co_fn = idHsWrapper
                              , bind_fvs = placeHolderNames
                              , fun_tick = [] }

    mkTopFunBind :: Origin -> Located Name -> [LMatch Name (LHsExpr Name)]
                 -> HsBind Name
    -- In Name-land, with empty bind_fvs
    mkTopFunBind origin fn ms = FunBind { fun_id = fn, fun_infix = False
                                        , fun_matches = mkMatchGroupName origin ms
                                        , fun_co_fn = idHsWrapper
                                        , bind_fvs = emptyNameSet -- NB: closed
                                                                  --     binding
                                        , fun_tick = [] }

    mkHsVarBind :: SrcSpan -> RdrName -> LHsExpr RdrName -> LHsBind RdrName
    mkHsVarBind loc var rhs = mk_easy_FunBind loc var [] rhs

    mkVarBind :: id -> LHsExpr id -> LHsBind id
    mkVarBind var rhs = L (getLoc rhs) $
                        VarBind { var_id = var, var_rhs = rhs, var_inline = False }

    mkPatSynBind :: Located RdrName -> HsPatSynDetails (Located RdrName)
                 -> LPat RdrName -> HsPatSynDir RdrName -> HsBind RdrName
    mkPatSynBind name details lpat dir = PatSynBind psb
      where
        psb = PSB{ psb_id = name
                 , psb_args = details
                 , psb_def = lpat
                 , psb_dir = dir
                 , psb_fvs = placeHolderNames }

    ------------
    mk_easy_FunBind :: SrcSpan -> RdrName -> [LPat RdrName]
                    -> LHsExpr RdrName -> LHsBind RdrName
    mk_easy_FunBind loc fun pats expr
      = L loc $ mkFunBind (L loc fun) [mkMatch pats expr emptyLocalBinds]

    ------------
    mkMatch :: [LPat id] -> LHsExpr id -> HsLocalBinds id -> LMatch id (LHsExpr id)
    mkMatch pats expr binds
      = noLoc (Match Nothing (map paren pats) Nothing
                     (GRHSs (unguardedRHS noSrcSpan expr) binds))
      where
        paren lp@(L l p) | hsPatNeedsParens p = L l (ParPat lp)
                         | otherwise          = lp

    {-
    ************************************************************************
    *                                                                      *
            Collecting binders
    *                                                                      *
    ************************************************************************

    Get all the binders in some HsBindGroups, IN THE ORDER OF APPEARANCE. eg.

    ...
    where
      (x, y) = ...
      f i j  = ...
      [a, b] = ...

    it should return [x, y, f, a, b] (remember, order important).

    Note [Collect binders only after renaming]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    These functions should only be used on HsSyn *after* the renamer,
    to return a [Name] or [Id].  Before renaming the record punning
    and wild-card mechanism makes it hard to know what is bound.
    So these functions should not be applied to (HsSyn RdrName)
    -}

    ----------------- Bindings --------------------------
    collectLocalBinders :: HsLocalBindsLR idL idR -> [idL]
    collectLocalBinders (HsValBinds binds) = collectHsIdBinders binds
                                             -- No pattern synonyms here
    collectLocalBinders (HsIPBinds _)      = []
    collectLocalBinders EmptyLocalBinds    = []

    collectHsIdBinders, collectHsValBinders :: HsValBindsLR idL idR -> [idL]
    -- Collect Id binders only, or Ids + pattern synonmys, respectively
    collectHsIdBinders  = collect_hs_val_binders True
    collectHsValBinders = collect_hs_val_binders False

    collectHsBindBinders :: HsBindLR idL idR -> [idL]
    -- Collect both Ids and pattern-synonym binders
    collectHsBindBinders b = collect_bind False b []

    collectHsBindsBinders :: LHsBindsLR idL idR -> [idL]
    collectHsBindsBinders binds = collect_binds False binds []

    collectHsBindListBinders :: [LHsBindLR idL idR] -> [idL]
    -- Same as collectHsBindsBinders, but works over a list of bindings
    collectHsBindListBinders = foldr (collect_bind False . unLoc) []

    collect_hs_val_binders :: Bool -> HsValBindsLR idL idR -> [idL]
    collect_hs_val_binders ps (ValBindsIn  binds _) = collect_binds     ps binds []
    collect_hs_val_binders ps (ValBindsOut binds _) = collect_out_binds ps binds

    collect_out_binds :: Bool -> [(RecFlag, LHsBinds id)] -> [id]
    collect_out_binds ps = foldr (collect_binds ps . snd) []

    collect_binds :: Bool -> LHsBindsLR idL idR -> [idL] -> [idL]
    -- Collect Ids, or Ids + patter synonyms, depending on boolean flag
    collect_binds ps binds acc = foldrBag (collect_bind ps . unLoc) acc binds

    collect_bind :: Bool -> HsBindLR idL idR -> [idL] -> [idL]
    collect_bind _ (PatBind { pat_lhs = p })           acc = collect_lpat p acc
    collect_bind _ (FunBind { fun_id = L _ f })        acc = f : acc
    collect_bind _ (VarBind { var_id = f })            acc = f : acc
    collect_bind _ (AbsBinds { abs_exports = dbinds }) acc = map abe_poly dbinds ++ acc
            -- I don't think we want the binders from the abe_binds
            -- The only time we collect binders from a typechecked
            -- binding (hence see AbsBinds) is in zonking in TcHsSyn
    collect_bind omitPatSyn (PatSynBind (PSB { psb_id = L _ ps })) acc =
        if omitPatSyn then acc else ps : acc

    collectMethodBinders :: LHsBindsLR RdrName idR -> [Located RdrName]
    -- Used exclusively for the bindings of an instance decl which are all FunBinds
    collectMethodBinders binds = foldrBag (get . unLoc) [] binds
      where
        get (FunBind { fun_id = f }) fs = f : fs
        get _                        fs = fs
           -- Someone else complains about non-FunBinds

    ----------------- Statements --------------------------
    collectLStmtsBinders :: [LStmtLR idL idR body] -> [idL]
    collectLStmtsBinders = concatMap collectLStmtBinders

    collectStmtsBinders :: [StmtLR idL idR body] -> [idL]
    collectStmtsBinders = concatMap collectStmtBinders

    collectLStmtBinders :: LStmtLR idL idR body -> [idL]
    collectLStmtBinders = collectStmtBinders . unLoc

    collectStmtBinders :: StmtLR idL idR body -> [idL]
      -- Id Binders for a Stmt... [but what about pattern-sig type vars]?
    collectStmtBinders (BindStmt pat _ _ _) = collectPatBinders pat
    collectStmtBinders (LetStmt binds)      = collectLocalBinders binds
    collectStmtBinders (BodyStmt {})        = []
    collectStmtBinders (LastStmt {})        = []
    collectStmtBinders (ParStmt xs _ _)     = collectLStmtsBinders
                                            $ [s | ParStmtBlock ss _ _ <- xs, s <- ss]
    collectStmtBinders (TransStmt { trS_stmts = stmts }) = collectLStmtsBinders stmts
    collectStmtBinders (RecStmt { recS_stmts = ss })     = collectLStmtsBinders ss

    ----------------- Patterns --------------------------
    collectPatBinders :: LPat a -> [a]
    collectPatBinders pat = collect_lpat pat []

    collectPatsBinders :: [LPat a] -> [a]
    collectPatsBinders pats = foldr collect_lpat [] pats

    -------------
    collect_lpat :: LPat name -> [name] -> [name]
    collect_lpat (L _ pat) bndrs
      = go pat
      where
        go (VarPat var)               = var : bndrs
        go (WildPat _)                = bndrs
        go (LazyPat pat)              = collect_lpat pat bndrs
        go (BangPat pat)              = collect_lpat pat bndrs
        go (AsPat (L _ a) pat)        = a : collect_lpat pat bndrs
        go (ViewPat _ pat _)          = collect_lpat pat bndrs
        go (ParPat  pat)              = collect_lpat pat bndrs

        go (ListPat pats _ _)         = foldr collect_lpat bndrs pats
        go (PArrPat pats _)           = foldr collect_lpat bndrs pats
        go (TuplePat pats _ _)        = foldr collect_lpat bndrs pats

        go (ConPatIn _ ps)            = foldr collect_lpat bndrs (hsConPatArgs ps)
        go (ConPatOut {pat_args=ps})  = foldr collect_lpat bndrs (hsConPatArgs ps)
            -- See Note [Dictionary binders in ConPatOut]
        go (LitPat _)                 = bndrs
        go (NPat _ _ _)               = bndrs
        go (NPlusKPat (L _ n) _ _ _)  = n : bndrs

        go (SigPatIn pat _)           = collect_lpat pat bndrs
        go (SigPatOut pat _)          = collect_lpat pat bndrs
        go (SplicePat _)              = bndrs
        go (QuasiQuotePat _)          = bndrs
        go (CoPat _ pat _)            = go pat

    {-
    Note [Dictionary binders in ConPatOut] See also same Note in DsArrows
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Do *not* gather (a) dictionary and (b) dictionary bindings as binders
    of a ConPatOut pattern.  For most calls it doesn't matter, because
    it's pre-typechecker and there are no ConPatOuts.  But it does matter
    more in the desugarer; for example, DsUtils.mkSelectorBinds uses
    collectPatBinders.  In a lazy pattern, for example f ~(C x y) = ...,
    we want to generate bindings for x,y but not for dictionaries bound by
    C.  (The type checker ensures they would not be used.)

    Desugaring of arrow case expressions needs these bindings (see DsArrows
    and arrowcase1), but SPJ (Jan 2007) says it's safer for it to use its
    own pat-binder-collector:

    Here's the problem.  Consider

    data T a where
       C :: Num a => a -> Int -> T a

    f ~(C (n+1) m) = (n,m)

    Here, the pattern (C (n+1)) binds a hidden dictionary (d::Num a),
    and *also* uses that dictionary to match the (n+1) pattern.  Yet, the
    variables bound by the lazy pattern are n,m, *not* the dictionary d.
    So in mkSelectorBinds in DsUtils, we want just m,n as the variables bound.
    -}

    hsGroupBinders :: HsGroup Name -> [Name]
    hsGroupBinders (HsGroup { hs_valds = val_decls, hs_tyclds = tycl_decls,
                              hs_instds = inst_decls, hs_fords = foreign_decls })
      =  collectHsValBinders val_decls
      ++ hsTyClForeignBinders tycl_decls inst_decls foreign_decls

    hsTyClForeignBinders :: [TyClGroup Name] -> [LInstDecl Name]
                         -> [LForeignDecl Name] -> [Name]
    -- We need to look at instance declarations too,
    -- because their associated types may bind data constructors
    hsTyClForeignBinders tycl_decls inst_decls foreign_decls
      = map unLoc $
        hsForeignDeclsBinders foreign_decls ++
        concatMap (concatMap hsLTyClDeclBinders . group_tyclds) tycl_decls ++
        concatMap hsLInstDeclBinders inst_decls

    -------------------
    hsLTyClDeclBinders :: Eq name => Located (TyClDecl name) -> [Located name]
    -- ^ Returns all the /binding/ names of the decl.
    -- The first one is guaranteed to be the name of the decl. For record fields
    -- mentioned in multiple constructors, the SrcLoc will be from the first
    -- occurrence.  We use the equality to filter out duplicate field names.
    --
    -- Each returned (Located name) has a SrcSpan for the /whole/ declaration.
    -- See Note [SrcSpan for binders]

    hsLTyClDeclBinders (L loc (FamDecl { tcdFam = FamilyDecl { fdLName = L _ name } }))
      = [L loc name]
    hsLTyClDeclBinders (L loc (SynDecl     { tcdLName = L _ name })) = [L loc name]
    hsLTyClDeclBinders (L loc (ClassDecl   { tcdLName = L _ cls_name
                                           , tcdSigs = sigs, tcdATs = ats }))
      = L loc cls_name :
        [ L fam_loc fam_name | L fam_loc (FamilyDecl { fdLName = L _ fam_name }) <- ats ] ++
        [ L mem_loc mem_name | L mem_loc (TypeSig ns _ _) <- sigs, L _ mem_name <- ns ]
    hsLTyClDeclBinders (L loc (DataDecl    { tcdLName = L _ name, tcdDataDefn = defn }))
      = L loc name : hsDataDefnBinders defn

    -------------------
    hsForeignDeclsBinders :: [LForeignDecl name] -> [Located name]
    -- See Note [SrcSpan for binders]
    hsForeignDeclsBinders foreign_decls
      = [ L decl_loc n
        | L decl_loc (ForeignImport (L _ n) _ _ _) <- foreign_decls]

    -------------------
    hsPatSynBinders :: LHsBindsLR idL idR -> [Located idL]
    -- Collect pattern-synonym binders only, not Ids
    -- See Note [SrcSpan for binders]
    hsPatSynBinders binds = foldrBag addPatSynBndr [] binds

    addPatSynBndr :: LHsBindLR idL idR -> [Located idL] -> [Located idL]
    -- See Note [SrcSpan for binders]
    addPatSynBndr bind pss
      | L bind_loc (PatSynBind (PSB { psb_id = L _ n })) <- bind
      = L bind_loc n : pss
      | otherwise
      = pss

    -------------------
    hsLInstDeclBinders :: Eq name => LInstDecl name -> [Located name]
    hsLInstDeclBinders (L _ (ClsInstD { cid_inst = ClsInstDecl { cid_datafam_insts = dfis } }))
      = concatMap (hsDataFamInstBinders . unLoc) dfis
    hsLInstDeclBinders (L _ (DataFamInstD { dfid_inst = fi }))
      = hsDataFamInstBinders fi
    hsLInstDeclBinders (L _ (TyFamInstD {})) = []

    -------------------
    -- the SrcLoc returned are for the whole declarations, not just the names
    hsDataFamInstBinders :: Eq name => DataFamInstDecl name -> [Located name]
    hsDataFamInstBinders (DataFamInstDecl { dfid_defn = defn })
      = hsDataDefnBinders defn
      -- There can't be repeated symbols because only data instances have binders

    -------------------
    -- the SrcLoc returned are for the whole declarations, not just the names
    hsDataDefnBinders :: Eq name => HsDataDefn name -> [Located name]
    hsDataDefnBinders (HsDataDefn { dd_cons = cons })
      = hsConDeclsBinders cons
      -- See Note [Binders in family instances]

    -------------------
    hsConDeclsBinders :: forall name. (Eq name) => [LConDecl name] -> [Located name]
      -- See hsLTyClDeclBinders for what this does
      -- The function is boringly complicated because of the records
      -- And since we only have equality, we have to be a little careful
    hsConDeclsBinders cons = go id cons
      where go :: ([Located name] -> [Located name]) -> [LConDecl name] -> [Located name]
            go _ [] = []
            go remSeen (r:rs) =
              -- don't re-mangle the location of field names, because we don't
              -- have a record of the full location of the field declaration anyway
              case r of
                 -- remove only the first occurrence of any seen field in order to
                 -- avoid circumventing detection of duplicate fields (#9156)
                 L loc (ConDecl { con_names = names, con_details = RecCon flds }) ->
                   (map (L loc . unLoc) names) ++ r' ++ go remSeen' rs
                      where r' = remSeen (concatMap (cd_fld_names . unLoc)
                                                    (unLoc flds))
                            remSeen' = foldr (.) remSeen [deleteBy ((==) `on` unLoc) v | v <- r']
                 L loc (ConDecl { con_names = names }) ->
                    (map (L loc . unLoc) names) ++ go remSeen rs

    {-

    Note [SrcSpan for binders]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~
    When extracting the (Located RdrNme) for a binder, at least for the
    main name (the TyCon of a type declaration etc), we want to give it
    the @SrcSpan@ of the whole /declaration/, not just the name itself
    (which is how it appears in the syntax tree).  This SrcSpan (for the
    entire declaration) is used as the SrcSpan for the Name that is
    finally produced, and hence for error messages.  (See Trac #8607.)

    Note [Binders in family instances]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    In a type or data family instance declaration, the type
    constructor is an *occurrence* not a binding site
        type instance T Int = Int -> Int   -- No binders
        data instance S Bool = S1 | S2     -- Binders are S1,S2

    ************************************************************************
    *                                                                      *
            Collecting binders the user did not write
    *                                                                      *
    ************************************************************************

    The job of this family of functions is to run through binding sites and find the set of all Names
    that were defined "implicitly", without being explicitly written by the user.

    The main purpose is to find names introduced by record wildcards so that we can avoid
    warning the user when they don't use those names (#4404)
    -}

    lStmtsImplicits :: [LStmtLR Name idR (Located (body idR))] -> NameSet
    lStmtsImplicits = hs_lstmts
      where
        hs_lstmts :: [LStmtLR Name idR (Located (body idR))] -> NameSet
        hs_lstmts = foldr (\stmt rest -> unionNameSet (hs_stmt (unLoc stmt)) rest) emptyNameSet

        hs_stmt (BindStmt pat _ _ _) = lPatImplicits pat
        hs_stmt (LetStmt binds)      = hs_local_binds binds
        hs_stmt (BodyStmt {})        = emptyNameSet
        hs_stmt (LastStmt {})        = emptyNameSet
        hs_stmt (ParStmt xs _ _)     = hs_lstmts [s | ParStmtBlock ss _ _ <- xs, s <- ss]
        hs_stmt (TransStmt { trS_stmts = stmts }) = hs_lstmts stmts
        hs_stmt (RecStmt { recS_stmts = ss })     = hs_lstmts ss

        hs_local_binds (HsValBinds val_binds) = hsValBindsImplicits val_binds
        hs_local_binds (HsIPBinds _)         = emptyNameSet
        hs_local_binds EmptyLocalBinds       = emptyNameSet

    hsValBindsImplicits :: HsValBindsLR Name idR -> NameSet
    hsValBindsImplicits (ValBindsOut binds _)
      = foldr (unionNameSet . lhsBindsImplicits . snd) emptyNameSet binds
    hsValBindsImplicits (ValBindsIn binds _)
      = lhsBindsImplicits binds

    lhsBindsImplicits :: LHsBindsLR Name idR -> NameSet
    lhsBindsImplicits = foldBag unionNameSet (lhs_bind . unLoc) emptyNameSet
      where
        lhs_bind (PatBind { pat_lhs = lpat }) = lPatImplicits lpat
        lhs_bind _ = emptyNameSet

    lPatImplicits :: LPat Name -> NameSet
    lPatImplicits = hs_lpat
      where
        hs_lpat (L _ pat) = hs_pat pat

        hs_lpats = foldr (\pat rest -> hs_lpat pat `unionNameSet` rest) emptyNameSet

        hs_pat (LazyPat pat)       = hs_lpat pat
        hs_pat (BangPat pat)       = hs_lpat pat
        hs_pat (AsPat _ pat)       = hs_lpat pat
        hs_pat (ViewPat _ pat _)   = hs_lpat pat
        hs_pat (ParPat  pat)       = hs_lpat pat
        hs_pat (ListPat pats _ _)  = hs_lpats pats
        hs_pat (PArrPat pats _)    = hs_lpats pats
        hs_pat (TuplePat pats _ _) = hs_lpats pats

        hs_pat (SigPatIn pat _)  = hs_lpat pat
        hs_pat (SigPatOut pat _) = hs_lpat pat
        hs_pat (CoPat _ pat _)   = hs_pat pat

        hs_pat (ConPatIn _ ps)           = details ps
        hs_pat (ConPatOut {pat_args=ps}) = details ps

        hs_pat _ = emptyNameSet

        details (PrefixCon ps)   = hs_lpats ps
        details (RecCon fs)      = hs_lpats explicit `unionNameSet` mkNameSet (collectPatsBinders implicit)
          where (explicit, implicit) = partitionEithers [if pat_explicit then Left pat else Right pat
                                                        | (i, fld) <- [0..] `zip` rec_flds fs
                                                        , let pat = hsRecFieldArg
                                                                         (unLoc fld)
                                                              pat_explicit = maybe True (i<) (rec_dotdot fs)]
        details (InfixCon p1 p2) = hs_lpat p1 `unionNameSet` hs_lpat p2