HsUtils.hs 41 KB
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{-
(c) The University of Glasgow, 1992-2006
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Here we collect a variety of helper functions that construct or
analyse HsSyn.  All these functions deal with generic HsSyn; functions
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which deal with the instantiated versions are located elsewhere:
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   Parameterised by     Module
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   ----------------     -------------
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   RdrName              parser/RdrHsSyn
   Name                 rename/RnHsSyn
   Id                   typecheck/TcHsSyn
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-}
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{-# LANGUAGE CPP #-}
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{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE FlexibleContexts #-}
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module HsUtils(
  -- Terms
  mkHsPar, mkHsApp, mkHsConApp, mkSimpleHsAlt,
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  mkSimpleMatch, unguardedGRHSs, unguardedRHS,
  mkMatchGroup, mkMatchGroupName, mkMatch, mkHsLam, mkHsIf,
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  mkHsWrap, mkLHsWrap, mkHsWrapCo, mkHsWrapCoR, mkLHsWrapCo,
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  coToHsWrapper, coToHsWrapperR, mkHsDictLet, mkHsLams,
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  mkHsOpApp, mkHsDo, mkHsComp, mkHsWrapPat, mkHsWrapPatCo,
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  mkLHsPar, mkHsCmdCast,
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  nlHsTyApp, nlHsTyApps, nlHsVar, nlHsLit, nlHsApp, nlHsApps, nlHsIntLit, nlHsVarApps,
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  nlHsDo, nlHsOpApp, nlHsLam, nlHsPar, nlHsIf, nlHsCase, nlList,
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  mkLHsTupleExpr, mkLHsVarTuple, missingTupArg,
  toHsType, toHsKind,
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  -- * Constructing general big tuples
  -- $big_tuples
  mkChunkified, chunkify,

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  -- Bindings
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  mkFunBind, mkVarBind, mkHsVarBind, mk_easy_FunBind, mkTopFunBind,
  mkPatSynBind,
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  -- Literals
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  mkHsIntegral, mkHsFractional, mkHsIsString, mkHsString,
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  -- Patterns
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  mkNPat, mkNPlusKPat, nlVarPat, nlLitPat, nlConVarPat, nlConVarPatName, nlConPat,
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  nlConPatName, nlInfixConPat, nlNullaryConPat, nlWildConPat, nlWildPat,
  nlWildPatName, nlWildPatId, nlTuplePat, mkParPat,
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  mkBigLHsVarTup, mkBigLHsTup, mkBigLHsVarPatTup, mkBigLHsPatTup,
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  -- Types
  mkHsAppTy, userHsTyVarBndrs,
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  nlHsAppTy, nlHsTyVar, nlHsFunTy, nlHsTyConApp,
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  -- Stmts
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  mkTransformStmt, mkTransformByStmt, mkBodyStmt, mkBindStmt, mkLastStmt,
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  emptyTransStmt, mkGroupUsingStmt, mkGroupByUsingStmt,
  emptyRecStmt, emptyRecStmtName, emptyRecStmtId, mkRecStmt,
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  -- Template Haskell
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  mkHsSpliceTy, mkHsSpliceE, mkHsSpliceTE, mkUntypedSplice,
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  mkHsQuasiQuote, unqualQuasiQuote,
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  -- Flags
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  noRebindableInfo,
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  -- Collecting binders
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  collectLocalBinders, collectHsValBinders, collectHsBindListBinders,
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  collectHsIdBinders,
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  collectHsBindsBinders, collectHsBindBinders, collectMethodBinders,
  collectPatBinders, collectPatsBinders,
  collectLStmtsBinders, collectStmtsBinders,
  collectLStmtBinders, collectStmtBinders,
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  hsLTyClDeclBinders, hsTyClForeignBinders, hsPatSynBinders,
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  hsForeignDeclsBinders, hsGroupBinders, hsDataFamInstBinders,
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  -- Collecting implicit binders
  lStmtsImplicits, hsValBindsImplicits, lPatImplicits
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  ) where
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#include "HsVersions.h"

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import HsDecls
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import HsBinds
import HsExpr
import HsPat
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import HsTypes
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import HsLit
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import PlaceHolder
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import TcEvidence
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import RdrName
import Var
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import TypeRep
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import TcType
import Kind
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import DataCon
import Name
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import NameSet
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import BasicTypes
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import SrcLoc
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import FastString
import Util
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import Bag
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import Outputable
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import Constants
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import Data.Either
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import Data.Function
import Data.List
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#if __GLASGOW_HASKELL__ < 709
import Data.Foldable ( foldMap )
import Data.Monoid ( mempty, mappend )
#endif

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{-
************************************************************************
*                                                                      *
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        Some useful helpers for constructing syntax
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*                                                                      *
************************************************************************
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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.
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-}
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mkHsPar :: LHsExpr id -> LHsExpr id
mkHsPar e = L (getLoc e) (HsPar e)

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mkSimpleMatch :: [LPat id] -> Located (body id) -> LMatch id (Located (body id))
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mkSimpleMatch pats rhs
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  = L loc $
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    Match Nothing pats Nothing (unguardedGRHSs rhs)
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  where
    loc = case pats of
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                []      -> getLoc rhs
                (pat:_) -> combineSrcSpans (getLoc pat) (getLoc rhs)
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unguardedGRHSs :: Located (body id) -> GRHSs id (Located (body id))
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unguardedGRHSs rhs@(L loc _) = GRHSs (unguardedRHS loc rhs) emptyLocalBinds
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unguardedRHS :: SrcSpan -> Located (body id) -> [LGRHS id (Located (body id))]
unguardedRHS loc rhs = [L loc (GRHS [] rhs)]
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mkMatchGroup :: Origin -> [LMatch RdrName (Located (body RdrName))]
             -> MatchGroup RdrName (Located (body RdrName))
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mkMatchGroup origin matches = MG { mg_alts = matches, mg_arg_tys = []
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                                 , mg_res_ty = placeHolderType
                                 , mg_origin = origin }

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

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mkHsLam :: [LPat RdrName] -> LHsExpr RdrName -> LHsExpr RdrName
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mkHsLam pats body = mkHsPar (L (getLoc body) (HsLam matches))
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        where
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          matches = mkMatchGroup Generated [mkSimpleMatch pats body]
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mkHsLams :: [TyVar] -> [EvVar] -> LHsExpr Id -> LHsExpr Id
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mkHsLams tyvars dicts expr = mkLHsWrap (mkWpTyLams tyvars
                                       <.> mkWpLams dicts) expr
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mkHsConApp :: DataCon -> [Type] -> [HsExpr Id] -> LHsExpr Id
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-- Used for constructing dictionary terms etc, so no locations
mkHsConApp data_con tys args
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  = foldl mk_app (nlHsTyApp (dataConWrapId data_con) tys) args
  where
    mk_app f a = noLoc (HsApp f (noLoc a))

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

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

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--------- 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

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

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mkHsIntegral   :: String -> Integer -> PostTc RdrName Type -> HsOverLit RdrName
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mkHsFractional :: FractionalLit -> PostTc RdrName Type -> HsOverLit RdrName
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mkHsIsString :: String -> FastString -> PostTc RdrName Type -> HsOverLit RdrName
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mkHsDo         :: HsStmtContext Name -> [ExprLStmt RdrName] -> HsExpr RdrName
mkHsComp       :: HsStmtContext Name -> [ExprLStmt RdrName] -> LHsExpr RdrName
               -> HsExpr RdrName
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mkNPat      :: Located (HsOverLit id) -> Maybe (SyntaxExpr id) -> Pat id
mkNPlusKPat :: Located id -> Located (HsOverLit id) -> Pat id
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mkLastStmt :: Located (bodyR idR) -> StmtLR idL idR (Located (bodyR idR))
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mkBodyStmt :: Located (bodyR RdrName)
           -> StmtLR idL RdrName (Located (bodyR RdrName))
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mkBindStmt :: LPat idL -> Located (bodyR idR) -> StmtLR idL idR (Located (bodyR idR))
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emptyRecStmt     :: StmtLR idL  RdrName bodyR
emptyRecStmtName :: StmtLR Name Name    bodyR
emptyRecStmtId   :: StmtLR Id   Id      bodyR
mkRecStmt    :: [LStmtLR idL RdrName bodyR] -> StmtLR idL RdrName bodyR
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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
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noRebindableInfo :: PlaceHolder
noRebindableInfo = PlaceHolder -- Just another placeholder;
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mkHsDo ctxt stmts = HsDo ctxt stmts placeHolderType
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mkHsComp ctxt stmts expr = mkHsDo ctxt (stmts ++ [last_stmt])
  where
    last_stmt = L (getLoc expr) $ mkLastStmt expr
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mkHsIf :: LHsExpr id -> LHsExpr id -> LHsExpr id -> HsExpr id
mkHsIf c a b = HsIf (Just noSyntaxExpr) c a b

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mkNPat lit neg     = NPat lit neg noSyntaxExpr
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mkNPlusKPat id lit = NPlusKPat id lit noSyntaxExpr noSyntaxExpr
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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)
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emptyTransStmt :: StmtLR idL idR (LHsExpr idR)
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emptyTransStmt = TransStmt { trS_form = panic "emptyTransStmt: form"
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                           , trS_stmts = [], trS_bndrs = []
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                           , trS_by = Nothing, trS_using = noLoc noSyntaxExpr
                           , trS_ret = noSyntaxExpr, trS_bind = noSyntaxExpr
                           , trS_fmap = noSyntaxExpr }
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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 }
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mkLastStmt body     = LastStmt body False noSyntaxExpr
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mkBodyStmt body     = BodyStmt body noSyntaxExpr noSyntaxExpr placeHolderType
mkBindStmt pat body = BindStmt pat body noSyntaxExpr noSyntaxExpr
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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 }
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-------------------------------
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--- A useful function for building @OpApps@.  The operator is always a
-- variable, and we don't know the fixity yet.
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mkHsOpApp :: LHsExpr id -> id -> LHsExpr id -> HsExpr id
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mkHsOpApp e1 op e2 = OpApp e1 (noLoc (HsVar op)) (error "mkOpApp:fixity") e2

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

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mkUntypedSplice :: LHsExpr RdrName -> HsSplice RdrName
mkUntypedSplice e = HsUntypedSplice unqualSplice e

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mkHsSpliceE :: LHsExpr RdrName -> HsExpr RdrName
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mkHsSpliceE e = HsSpliceE (mkUntypedSplice e)
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mkHsSpliceTE :: LHsExpr RdrName -> HsExpr RdrName
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mkHsSpliceTE e = HsSpliceE (HsTypedSplice unqualSplice e)
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mkHsSpliceTy :: LHsExpr RdrName -> HsType RdrName
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mkHsSpliceTy e = HsSpliceTy (HsUntypedSplice unqualSplice e) placeHolderKind
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mkHsQuasiQuote :: RdrName -> SrcSpan -> FastString -> HsSplice RdrName
mkHsQuasiQuote quoter span quote = HsQuasiQuote unqualSplice quoter span quote
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unqualQuasiQuote :: RdrName
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unqualQuasiQuote = mkRdrUnqual (mkVarOccFS (fsLit "quasiquote"))
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                -- A name (uniquified later) to
                -- identify the quasi-quote
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mkHsString :: String -> HsLit
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mkHsString s = HsString s (mkFastString s)
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-------------
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userHsTyVarBndrs :: SrcSpan -> [name] -> [Located (HsTyVarBndr name)]
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-- Caller sets location
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userHsTyVarBndrs loc bndrs = [ L loc (UserTyVar v) | v <- bndrs ]
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{-
************************************************************************
*                                                                      *
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        Constructing syntax with no location info
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*                                                                      *
************************************************************************
-}
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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)

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nlHsIntLit :: Integer -> LHsExpr id
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nlHsIntLit n = noLoc (HsLit (HsInt (show n) n))
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nlHsApps :: id -> [LHsExpr id] -> LHsExpr id
nlHsApps f xs = foldl nlHsApp (nlHsVar f) xs
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nlHsVarApps :: id -> [id] -> LHsExpr id
nlHsVarApps f xs = noLoc (foldl mk (HsVar f) (map HsVar xs))
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                 where
                   mk f a = HsApp (noLoc f) (noLoc a)
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nlConVarPat :: RdrName -> [RdrName] -> LPat RdrName
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nlConVarPat con vars = nlConPat con (map nlVarPat vars)

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nlConVarPatName :: Name -> [Name] -> LPat Name
nlConVarPatName con vars = nlConPatName con (map nlVarPat vars)

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

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

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

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

nlWildConPat :: DataCon -> LPat RdrName
nlWildConPat con = noLoc (ConPatIn (noLoc (getRdrName con))
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                         (PrefixCon (nOfThem (dataConSourceArity con)
                                             nlWildPat)))
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nlWildPat :: LPat RdrName
nlWildPat  = noLoc (WildPat placeHolderType )  -- Pre-typechecking
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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
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nlHsDo ctxt stmts = noLoc (mkHsDo ctxt stmts)
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nlHsOpApp :: LHsExpr id -> id -> LHsExpr id -> LHsExpr id
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nlHsOpApp e1 op e2 = noLoc (mkHsOpApp e1 op e2)

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nlHsLam  :: LMatch RdrName (LHsExpr RdrName) -> LHsExpr RdrName
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nlHsPar  :: LHsExpr id -> LHsExpr id
nlHsIf   :: LHsExpr id -> LHsExpr id -> LHsExpr id -> LHsExpr id
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nlHsCase :: LHsExpr RdrName -> [LMatch RdrName (LHsExpr RdrName)]
         -> LHsExpr RdrName
nlList   :: [LHsExpr RdrName] -> LHsExpr RdrName
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nlHsLam match          = noLoc (HsLam (mkMatchGroup Generated [match]))
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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)
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nlHsAppTy :: LHsType name -> LHsType name -> LHsType name
nlHsTyVar :: name                         -> LHsType name
nlHsFunTy :: LHsType name -> LHsType name -> LHsType name

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nlHsAppTy f t           = noLoc (HsAppTy f t)
nlHsTyVar x             = noLoc (HsTyVar x)
nlHsFunTy a b           = noLoc (HsFunTy a b)
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nlHsTyConApp :: name -> [LHsType name] -> LHsType name
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nlHsTyConApp tycon tys  = foldl nlHsAppTy (nlHsTyVar tycon) tys
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{-
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Tuples.  All these functions are *pre-typechecker* because they lack
types on the tuple.
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-}
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mkLHsTupleExpr :: [LHsExpr a] -> LHsExpr a
-- Makes a pre-typechecker boxed tuple, deals with 1 case
mkLHsTupleExpr [e] = e
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mkLHsTupleExpr es  = noLoc $ ExplicitTuple (map (noLoc . Present) es) Boxed
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mkLHsVarTuple :: [a] -> LHsExpr a
mkLHsVarTuple ids  = mkLHsTupleExpr (map nlHsVar ids)
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nlTuplePat :: [LPat id] -> Boxity -> LPat id
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nlTuplePat pats box = noLoc (TuplePat pats box [])
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missingTupArg :: HsTupArg RdrName
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missingTupArg = Missing placeHolderType
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mkLHsPatTup :: [LPat id] -> LPat id
mkLHsPatTup []     = noLoc $ TuplePat [] Boxed []
mkLHsPatTup [lpat] = lpat
mkLHsPatTup lpats  = L (getLoc (head lpats)) $ TuplePat lpats Boxed []

-- The Big equivalents for the source tuple expressions
mkBigLHsVarTup :: [id] -> LHsExpr id
mkBigLHsVarTup ids = mkBigLHsTup (map nlHsVar ids)

mkBigLHsTup :: [LHsExpr id] -> LHsExpr id
mkBigLHsTup = mkChunkified mkLHsTupleExpr

-- The Big equivalents for the source tuple patterns
mkBigLHsVarPatTup :: [id] -> LPat id
mkBigLHsVarPatTup bs = mkBigLHsPatTup (map nlVarPat bs)

mkBigLHsPatTup :: [LPat id] -> LPat id
mkBigLHsPatTup = mkChunkified mkLHsPatTup

-- $big_tuples
-- #big_tuples#
--
-- GHCs built in tuples can only go up to 'mAX_TUPLE_SIZE' in arity, but
-- we might concievably want to build such a massive tuple as part of the
-- output of a desugaring stage (notably that for list comprehensions).
--
-- We call tuples above this size \"big tuples\", and emulate them by
-- creating and pattern matching on >nested< tuples that are expressible
-- by GHC.
--
-- Nesting policy: it's better to have a 2-tuple of 10-tuples (3 objects)
-- than a 10-tuple of 2-tuples (11 objects), so we want the leaves of any
-- construction to be big.
--
-- If you just use the 'mkBigCoreTup', 'mkBigCoreVarTupTy', 'mkTupleSelector'
-- and 'mkTupleCase' functions to do all your work with tuples you should be
-- fine, and not have to worry about the arity limitation at all.

-- | Lifts a \"small\" constructor into a \"big\" constructor by recursive decompositon
mkChunkified :: ([a] -> a)      -- ^ \"Small\" constructor function, of maximum input arity 'mAX_TUPLE_SIZE'
             -> [a]             -- ^ Possible \"big\" list of things to construct from
             -> a               -- ^ Constructed thing made possible by recursive decomposition
mkChunkified small_tuple as = mk_big_tuple (chunkify as)
  where
        -- Each sub-list is short enough to fit in a tuple
    mk_big_tuple [as] = small_tuple as
    mk_big_tuple as_s = mk_big_tuple (chunkify (map small_tuple as_s))

chunkify :: [a] -> [[a]]
-- ^ Split a list into lists that are small enough to have a corresponding
-- tuple arity. The sub-lists of the result all have length <= 'mAX_TUPLE_SIZE'
-- But there may be more than 'mAX_TUPLE_SIZE' sub-lists
chunkify xs
  | n_xs <= mAX_TUPLE_SIZE = [xs]
  | otherwise              = split xs
  where
    n_xs     = length xs
    split [] = []
    split xs = take mAX_TUPLE_SIZE xs : split (drop mAX_TUPLE_SIZE xs)

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{-
************************************************************************
*                                                                      *
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        Converting a Type to an HsType RdrName
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*                                                                      *
************************************************************************
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This is needed to implement GeneralizedNewtypeDeriving.
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-}
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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)
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    to_hs_type (TyConApp tc args) = nlHsTyConApp (getRdrName tc) (map toHsType args')
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       where
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         args' = filterOut isKind args
         -- Source-language types have _implicit_ kind arguments,
         -- so we must remove them here (Trac #8563)
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    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)
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    to_hs_type (LitTy (NumTyLit n)) = noLoc $ HsTyLit (HsNumTy "" n)
    to_hs_type (LitTy (StrTyLit s)) = noLoc $ HsTyLit (HsStrTy "" s)
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    mk_hs_tvb tv = noLoc $ KindedTyVar (noLoc (getRdrName tv))
                                       (toHsKind (tyVarKind tv))
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toHsKind :: Kind -> LHsKind RdrName
toHsKind = toHsType

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--------- 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
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                 | otherwise           = HsWrap co_fn e
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mkHsWrapCo :: TcCoercionN   -- A Nominal coercion  a ~N b
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           -> HsExpr id -> HsExpr id
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mkHsWrapCo co e = mkHsWrap (coToHsWrapper co) e
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mkHsWrapCoR :: TcCoercionR   -- A Representational coercion  a ~R b
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            -> HsExpr id -> HsExpr id
mkHsWrapCoR co e = mkHsWrap (coToHsWrapperR co) e

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mkLHsWrapCo :: TcCoercion -> LHsExpr id -> LHsExpr id
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mkLHsWrapCo co (L loc e) = L loc (mkHsWrapCo co e)
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mkHsCmdCast :: TcCoercion -> HsCmd id -> HsCmd id
mkHsCmdCast co cmd | isTcReflCo co = cmd
                   | otherwise     = HsCmdCast co cmd

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

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mkHsWrapPat :: HsWrapper -> Pat id -> Type -> Pat id
mkHsWrapPat co_fn p ty | isIdHsWrapper co_fn = p
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                       | otherwise           = CoPat co_fn p ty
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-- input coercion is Nominal
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mkHsWrapPatCo :: TcCoercion -> Pat id -> Type -> Pat id
mkHsWrapPatCo co pat ty | isTcReflCo co = pat
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                        | otherwise     = CoPat (mkWpCast (mkTcSubCo co)) pat ty
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mkHsDictLet :: TcEvBinds -> LHsExpr Id -> LHsExpr Id
mkHsDictLet ev_binds expr = mkLHsWrap (mkWpLet ev_binds) expr
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{-
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l
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************************************************************************
*                                                                      *
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                Bindings; with a location at the top
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*                                                                      *
************************************************************************
-}
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mkFunBind :: Located RdrName -> [LMatch RdrName (LHsExpr RdrName)]
          -> HsBind RdrName
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-- Not infix, with place holders for coercion and free vars
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mkFunBind fn ms = FunBind { fun_id = fn, fun_infix = False
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                          , fun_matches = mkMatchGroup Generated ms
                          , fun_co_fn = idHsWrapper
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                          , bind_fvs = placeHolderNames
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                          , fun_tick = [] }
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mkTopFunBind :: Origin -> Located Name -> [LMatch Name (LHsExpr Name)]
             -> HsBind Name
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-- In Name-land, with empty bind_fvs
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mkTopFunBind origin fn ms = FunBind { fun_id = fn, fun_infix = False
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                                    , fun_matches = mkMatchGroupName origin ms
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                                    , fun_co_fn = idHsWrapper
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                                    , bind_fvs = emptyNameSet -- NB: closed
                                                              --     binding
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                                    , fun_tick = [] }
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mkHsVarBind :: SrcSpan -> RdrName -> LHsExpr RdrName -> LHsBind RdrName
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mkHsVarBind loc var rhs = mk_easy_FunBind loc var [] rhs

mkVarBind :: id -> LHsExpr id -> LHsBind id
mkVarBind var rhs = L (getLoc rhs) $
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                    VarBind { var_id = var, var_rhs = rhs, var_inline = False }
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mkPatSynBind :: Located RdrName -> HsPatSynDetails (Located RdrName)
             -> LPat RdrName -> HsPatSynDir RdrName -> HsBind RdrName
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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 }
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------------
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mk_easy_FunBind :: SrcSpan -> RdrName -> [LPat RdrName]
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                -> LHsExpr RdrName -> LHsBind RdrName
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mk_easy_FunBind loc fun pats expr
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  = L loc $ mkFunBind (L loc fun) [mkMatch pats expr emptyLocalBinds]
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------------
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mkMatch :: [LPat id] -> LHsExpr id -> HsLocalBinds id -> LMatch id (LHsExpr id)
mkMatch pats expr binds
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  = noLoc (Match Nothing (map paren pats) Nothing
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                 (GRHSs (unguardedRHS noSrcSpan expr) binds))
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  where
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    paren lp@(L l p) | hsPatNeedsParens p = L l (ParPat lp)
                     | otherwise          = lp
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{-
************************************************************************
*                                                                      *
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        Collecting binders
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*                                                                      *
************************************************************************
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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).

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Note [Collect binders only after renaming]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
These functions should only be used on HsSyn *after* the renamer,
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to return a [Name] or [Id].  Before renaming the record punning
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and wild-card mechanism makes it hard to know what is bound.
So these functions should not be applied to (HsSyn RdrName)
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-}
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----------------- Bindings --------------------------
collectLocalBinders :: HsLocalBindsLR idL idR -> [idL]
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collectLocalBinders (HsValBinds binds) = collectHsIdBinders binds
                                         -- No pattern synonyms here
collectLocalBinders (HsIPBinds _)      = []
collectLocalBinders EmptyLocalBinds    = []
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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
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collectHsBindBinders :: HsBindLR idL idR -> [idL]
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-- Collect both Ids and pattern-synonym binders
collectHsBindBinders b = collect_bind False b []
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collectHsBindsBinders :: LHsBindsLR idL idR -> [idL]
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collectHsBindsBinders binds = collect_binds False binds []
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collectHsBindListBinders :: [LHsBindLR idL idR] -> [idL]
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-- 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
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collectMethodBinders :: LHsBindsLR RdrName idR -> [Located RdrName]
-- Used exclusively for the bindings of an instance decl which are all FunBinds
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collectMethodBinders binds = foldrBag (get . unLoc) [] binds
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  where
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    get (FunBind { fun_id = f }) fs = f : fs
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    get _                        fs = fs
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       -- Someone else complains about non-FunBinds
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----------------- Statements --------------------------
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collectLStmtsBinders :: [LStmtLR idL idR body] -> [idL]
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collectLStmtsBinders = concatMap collectLStmtBinders
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collectStmtsBinders :: [StmtLR idL idR body] -> [idL]
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collectStmtsBinders = concatMap collectStmtBinders

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

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collectStmtBinders :: StmtLR idL idR body -> [idL]
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  -- Id Binders for a Stmt... [but what about pattern-sig type vars]?
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collectStmtBinders (BindStmt pat _ _ _) = collectPatBinders pat
collectStmtBinders (LetStmt binds)      = collectLocalBinders binds
collectStmtBinders (BodyStmt {})        = []
collectStmtBinders (LastStmt {})        = []
collectStmtBinders (ParStmt xs _ _)     = collectLStmtsBinders
                                        $ [s | ParStmtBlock ss _ _ <- xs, s <- ss]
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collectStmtBinders (TransStmt { trS_stmts = stmts }) = collectLStmtsBinders stmts
collectStmtBinders (RecStmt { recS_stmts = ss })     = collectLStmtsBinders ss
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collectStmtBinders ApplicativeStmt{} = []
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----------------- Patterns --------------------------
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collectPatBinders :: LPat a -> [a]
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collectPatBinders pat = collect_lpat pat []
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collectPatsBinders :: [LPat a] -> [a]
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collectPatsBinders pats = foldr collect_lpat [] pats
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-------------
collect_lpat :: LPat name -> [name] -> [name]
collect_lpat (L _ pat) bndrs
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  = go pat
  where
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    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
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    go (ViewPat _ pat _)          = collect_lpat pat bndrs
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    go (ParPat  pat)              = collect_lpat pat bndrs

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

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    go (ConPatIn _ ps)            = foldr collect_lpat bndrs (hsConPatArgs ps)
    go (ConPatOut {pat_args=ps})  = foldr collect_lpat bndrs (hsConPatArgs ps)
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        -- See Note [Dictionary binders in ConPatOut]
    go (LitPat _)                 = bndrs
    go (NPat _ _ _)               = bndrs
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    go (NPlusKPat (L _ n) _ _ _)  = n : bndrs
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    go (SigPatIn pat _)           = collect_lpat pat bndrs
    go (SigPatOut pat _)          = collect_lpat pat bndrs
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    go (SplicePat _)              = bndrs
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    go (CoPat _ pat _)            = go pat
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{-
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Note [Dictionary binders in ConPatOut] See also same Note in DsArrows
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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.)

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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.
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-}
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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
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  ++ hsTyClForeignBinders tycl_decls inst_decls foreign_decls
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hsTyClForeignBinders :: [TyClGroup Name] -> [LInstDecl Name]
                     -> [LForeignDecl Name] -> [Name]
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-- We need to look at instance declarations too,
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-- because their associated types may bind data constructors
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hsTyClForeignBinders tycl_decls inst_decls foreign_decls
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  = map unLoc (hsForeignDeclsBinders foreign_decls)
    ++ getSelectorNames (foldMap (foldMap hsLTyClDeclBinders . group_tyclds) tycl_decls
                        `mappend` foldMap hsLInstDeclBinders inst_decls)
  where
    getSelectorNames :: ([Located Name], [LFieldOcc Name]) -> [Name]
    getSelectorNames (ns, fs) = map unLoc ns ++ map (selectorFieldOcc.unLoc) fs
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-------------------
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hsLTyClDeclBinders :: Located (TyClDecl name) -> ([Located name], [LFieldOcc name])
-- ^ Returns all the /binding/ names of the decl.  The first one is
-- guaranteed to be the name of the decl. The first component
-- represents all binding names except record fields; the second
-- represents field occurrences. For record fields mentioned in
-- multiple constructors, the SrcLoc will be from the first occurrence.
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--
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-- Each returned (Located name) has a SrcSpan for the /whole/ declaration.
-- See Note [SrcSpan for binders]
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hsLTyClDeclBinders (L loc (FamDecl { tcdFam = FamilyDecl { fdLName = L _ name } }))
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  = ([L loc name], [])
hsLTyClDeclBinders (L loc (SynDecl     { tcdLName = L _ name })) = ([L loc name], [])
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hsLTyClDeclBinders (L loc (ClassDecl   { tcdLName = L _ cls_name
                                       , tcdSigs = sigs, tcdATs = ats }))
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  = (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 ]
    , [])
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hsLTyClDeclBinders (L loc (DataDecl    { tcdLName = L _ name, tcdDataDefn = defn }))
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  = (\ (xs, ys) -> (L loc name : xs, ys)) $ hsDataDefnBinders defn
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-------------------
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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]

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-------------------
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hsPatSynBinders :: HsValBinds RdrName
                -> ([Located RdrName], [Located RdrName])
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-- Collect pattern-synonym binders only, not Ids
-- See Note [SrcSpan for binders]
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hsPatSynBinders (ValBindsIn binds _) = foldrBag addPatSynBndr ([],[]) binds
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hsPatSynBinders _ = panic "hsPatSynBinders"
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addPatSynBndr :: LHsBindLR id id -> ([Located id], [Located id])
                -> ([Located id], [Located id]) -- (selectors, other)
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-- See Note [SrcSpan for binders]
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addPatSynBndr bind (sels, pss)
  | L bind_loc (PatSynBind (PSB { psb_id = L _ n
                                , psb_args = RecordPatSyn as })) <- bind
  = (map recordPatSynSelectorId as ++ sels, L bind_loc n : pss)
  | L bind_loc (PatSynBind (PSB { psb_id = L _ n})) <- bind
  = (sels, L bind_loc n : pss)
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  | otherwise
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  = (sels, pss)
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-------------------
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hsLInstDeclBinders :: LInstDecl name -> ([Located name], [LFieldOcc name])
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hsLInstDeclBinders (L _ (ClsInstD { cid_inst = ClsInstDecl { cid_datafam_insts = dfis } }))
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  = foldMap (hsDataFamInstBinders . unLoc) dfis
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hsLInstDeclBinders (L _ (DataFamInstD { dfid_inst = fi }))
  = hsDataFamInstBinders fi
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hsLInstDeclBinders (L _ (TyFamInstD {})) = mempty
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-------------------
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-- the SrcLoc returned are for the whole declarations, not just the names
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hsDataFamInstBinders :: DataFamInstDecl name -> ([Located name], [LFieldOcc name])
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hsDataFamInstBinders (DataFamInstDecl { dfid_defn = defn })
  = hsDataDefnBinders defn
  -- There can't be repeated symbols because only data instances have binders
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-------------------
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-- the SrcLoc returned are for the whole declarations, not just the names
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hsDataDefnBinders :: HsDataDefn name -> ([Located name], [LFieldOcc name])
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hsDataDefnBinders (HsDataDefn { dd_cons = cons })
  = hsConDeclsBinders cons
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  -- See Note [Binders in family instances]
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-------------------
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hsConDeclsBinders :: [LConDecl name] -> ([Located name], [LFieldOcc name])
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  -- See hsLTyClDeclBinders for what this does
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  -- The function is boringly complicated because of the records
  -- And since we only have equality, we have to be a little careful
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hsConDeclsBinders cons = go id cons
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  where go :: ([LFieldOcc name] -> [LFieldOcc name])
           -> [LConDecl name] -> ([Located name], [LFieldOcc name])
        go _ [] = ([], [])
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        go remSeen (r:rs) =
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          -- 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
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          case r of
             -- remove only the first occurrence of any seen field in order to
             -- avoid circumventing detection of duplicate fields (#9156)
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             L loc (ConDecl { con_names = names, con_details = RecCon flds }) ->
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               (map (L loc . unLoc) names ++ ns, r' ++ fs)
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                  where r' = remSeen (concatMap (cd_fld_names . unLoc)
                                                (unLoc flds))
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                        remSeen' = foldr (.) remSeen [deleteBy ((==) `on` rdrNameFieldOcc . unLoc) v | v <- r']
                        (ns, fs) = go remSeen' rs
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             L loc (ConDecl { con_names = names }) ->
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                (map (L loc . unLoc) names ++ ns, fs)
                  where (ns, fs) = go remSeen rs
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{-
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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.)

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Note [Binders in family instances]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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In a type or data family instance declaration, the type
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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

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        Collecting binders the user did not write
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