TcHsSyn.hs 70.8 KB
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{-
(c) The University of Glasgow 2006
(c) The AQUA Project, Glasgow University, 1996-1998

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TcHsSyn: Specialisations of the @HsSyn@ syntax for the typechecker
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This module is an extension of @HsSyn@ syntax, for use in the type
checker.
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-}
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{-# LANGUAGE CPP, TupleSections #-}
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module TcHsSyn (
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        mkHsConApp, mkHsDictLet, mkHsApp,
        hsLitType, hsLPatType, hsPatType,
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        mkHsAppTy, mkHsCaseAlt,
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        nlHsIntLit,
        shortCutLit, hsOverLitName,
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        conLikeResTy,
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        -- * re-exported from TcMonad
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        TcId, TcIdSet,

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        -- * Zonking
        -- | For a description of "zonking", see Note [What is zonking?]
        -- in TcMType
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        zonkTopDecls, zonkTopExpr, zonkTopLExpr,
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        zonkTopBndrs, zonkTyBndrsX,
        zonkTyConBinders,
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        emptyZonkEnv, mkEmptyZonkEnv,
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        zonkTcTypeToType, zonkTcTypeToTypes, zonkTyVarOcc,
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        zonkCoToCo,
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        zonkEvBinds,
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        -- * Validity checking
        checkForRepresentationPolymorphism
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  ) where

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#include "HsVersions.h"
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import HsSyn
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import Id
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import TcRnMonad
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import PrelNames
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import TcType
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import TcMType
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import TcEvidence
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import TysPrim
import TysWiredIn
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import Type
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import TyCon
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import Coercion
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import ConLike
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import DataCon
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import HscTypes
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import Name
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import NameEnv
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import Var
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import VarSet
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import VarEnv
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import DynFlags
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import Literal
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import BasicTypes
import Maybes
import SrcLoc
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import Bag
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import Outputable
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import Util
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import UniqFM
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import Control.Monad
import Data.List  ( partition )
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import Control.Arrow ( second )
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{-
************************************************************************
*                                                                      *
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\subsection[mkFailurePair]{Code for pattern-matching and other failures}
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*                                                                      *
************************************************************************
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Note: If @hsLPatType@ doesn't bear a strong resemblance to @exprType@,
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then something is wrong.
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-}

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hsLPatType :: OutPat Id -> Type
hsLPatType (L _ pat) = hsPatType pat

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hsPatType :: Pat Id -> Type
hsPatType (ParPat pat)                = hsLPatType pat
hsPatType (WildPat ty)                = ty
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hsPatType (VarPat (L _ var))          = idType var
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hsPatType (BangPat pat)               = hsLPatType pat
hsPatType (LazyPat pat)               = hsLPatType pat
hsPatType (LitPat lit)                = hsLitType lit
hsPatType (AsPat var _)               = idType (unLoc var)
hsPatType (ViewPat _ _ ty)            = ty
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hsPatType (ListPat _ ty Nothing)      = mkListTy ty
hsPatType (ListPat _ _ (Just (ty,_))) = ty
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hsPatType (PArrPat _ ty)              = mkPArrTy ty
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hsPatType (TuplePat _ bx tys)         = mkTupleTy bx tys
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hsPatType (ConPatOut { pat_con = L _ con, pat_arg_tys = tys })
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                                      = conLikeResTy con tys
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hsPatType (SigPatOut _ ty)            = ty
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hsPatType (NPat _ _ _ ty)             = ty
hsPatType (NPlusKPat _ _ _ _ _ ty)    = ty
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hsPatType (CoPat _ _ ty)              = ty
hsPatType p                           = pprPanic "hsPatType" (ppr p)
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hsLitType :: HsLit -> TcType
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hsLitType (HsChar _ _)       = charTy
hsLitType (HsCharPrim _ _)   = charPrimTy
hsLitType (HsString _ _)     = stringTy
hsLitType (HsStringPrim _ _) = addrPrimTy
hsLitType (HsInt _ _)        = intTy
hsLitType (HsIntPrim _ _)    = intPrimTy
hsLitType (HsWordPrim _ _)   = wordPrimTy
hsLitType (HsInt64Prim _ _)  = int64PrimTy
hsLitType (HsWord64Prim _ _) = word64PrimTy
hsLitType (HsInteger _ _ ty) = ty
hsLitType (HsRat _ ty)       = ty
hsLitType (HsFloatPrim _)    = floatPrimTy
hsLitType (HsDoublePrim _)   = doublePrimTy
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-- Overloaded literals. Here mainly because it uses isIntTy etc
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shortCutLit :: DynFlags -> OverLitVal -> TcType -> Maybe (HsExpr TcId)
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shortCutLit dflags (HsIntegral src i) ty
  | isIntTy ty  && inIntRange  dflags i = Just (HsLit (HsInt src i))
  | isWordTy ty && inWordRange dflags i
                                   = Just (mkLit wordDataCon (HsWordPrim src i))
  | isIntegerTy ty = Just (HsLit (HsInteger src i ty))
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  | otherwise = shortCutLit dflags (HsFractional (integralFractionalLit i)) ty
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        -- The 'otherwise' case is important
        -- Consider (3 :: Float).  Syntactically it looks like an IntLit,
        -- so we'll call shortCutIntLit, but of course it's a float
        -- This can make a big difference for programs with a lot of
        -- literals, compiled without -O
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shortCutLit _ (HsFractional f) ty
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  | isFloatTy ty  = Just (mkLit floatDataCon  (HsFloatPrim f))
  | isDoubleTy ty = Just (mkLit doubleDataCon (HsDoublePrim f))
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  | otherwise     = Nothing

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shortCutLit _ (HsIsString src s) ty
  | isStringTy ty = Just (HsLit (HsString src s))
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  | otherwise     = Nothing

mkLit :: DataCon -> HsLit -> HsExpr Id
mkLit con lit = HsApp (nlHsVar (dataConWrapId con)) (nlHsLit lit)

------------------------------
hsOverLitName :: OverLitVal -> Name
-- Get the canonical 'fromX' name for a particular OverLitVal
hsOverLitName (HsIntegral {})   = fromIntegerName
hsOverLitName (HsFractional {}) = fromRationalName
hsOverLitName (HsIsString {})   = fromStringName
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{-
************************************************************************
*                                                                      *
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\subsection[BackSubst-HsBinds]{Running a substitution over @HsBinds@}
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*                                                                      *
************************************************************************
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The rest of the zonking is done *after* typechecking.
The main zonking pass runs over the bindings
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 a) to convert TcTyVars to TyVars etc, dereferencing any bindings etc
 b) convert unbound TcTyVar to Void
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 c) convert each TcId to an Id by zonking its type
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The type variables are converted by binding mutable tyvars to immutable ones
and then zonking as normal.
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The Ids are converted by binding them in the normal Tc envt; that
way we maintain sharing; eg an Id is zonked at its binding site and they
all occurrences of that Id point to the common zonked copy
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It's all pretty boring stuff, because HsSyn is such a large type, and
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the environment manipulation is tiresome.
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-}
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-- Confused by zonking? See Note [What is zonking?] in TcMType.
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type UnboundTyVarZonker = TcTyVar -> TcM Type
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        -- How to zonk an unbound type variable
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        -- Note [Zonking the LHS of a RULE]

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-- | A ZonkEnv carries around several bits.
-- The UnboundTyVarZonker just zaps unbouned meta-tyvars to Any (as
-- defined in zonkTypeZapping), except on the LHS of rules. See
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-- Note [Zonking the LHS of a RULE].
--
-- The (TyCoVarEnv TyVar) and is just an optimisation: when binding a
-- tyvar or covar, we zonk the kind right away and add a mapping to
-- the env. This prevents re-zonking the kind at every occurrence. But
-- this is *just* an optimisation.
--
-- The final (IdEnv Var) optimises zonking for Ids. It is
-- knot-tied. We must be careful never to put coercion variables
-- (which are Ids, after all) in the knot-tied env, because coercions
-- can appear in types, and we sometimes inspect a zonked type in this
-- module.
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--
-- Confused by zonking? See Note [What is zonking?] in TcMType.
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data ZonkEnv
  = ZonkEnv
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      UnboundTyVarZonker
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      (TyCoVarEnv TyVar)
      (IdEnv      Var)         -- What variables are in scope
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        -- Maps an Id or EvVar to its zonked version; both have the same Name
        -- Note that all evidence (coercion variables as well as dictionaries)
        --      are kept in the ZonkEnv
        -- Only *type* abstraction is done by side effect
        -- Is only consulted lazily; hence knot-tying

instance Outputable ZonkEnv where
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  ppr (ZonkEnv _ _ty_env var_env) = pprUFM var_env (vcat . map ppr)
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-- The EvBinds have to already be zonked, but that's usually the case.
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emptyZonkEnv :: ZonkEnv
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emptyZonkEnv = mkEmptyZonkEnv zonkTypeZapping

mkEmptyZonkEnv :: UnboundTyVarZonker -> ZonkEnv
mkEmptyZonkEnv zonker = ZonkEnv zonker emptyVarEnv emptyVarEnv
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-- | Extend the knot-tied environment.
extendIdZonkEnvRec :: ZonkEnv -> [Var] -> ZonkEnv
extendIdZonkEnvRec (ZonkEnv zonk_ty ty_env id_env) ids
    -- NB: Don't look at the var to decide which env't to put it in. That
    -- would end up knot-tying all the env'ts.
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  = ZonkEnv zonk_ty ty_env (extendVarEnvList id_env [(id,id) | id <- ids])
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  -- Given coercion variables will actually end up here. That's OK though:
  -- coercion variables are never looked up in the knot-tied env't, so zonking
  -- them simply doesn't get optimised. No one gets hurt. An improvement (?)
  -- would be to do SCC analysis in zonkEvBinds and then only knot-tie the
  -- recursive groups. But perhaps the time it takes to do the analysis is
  -- more than the savings.

extendZonkEnv :: ZonkEnv -> [Var] -> ZonkEnv
extendZonkEnv (ZonkEnv zonk_ty tyco_env id_env) vars
  = ZonkEnv zonk_ty (extendVarEnvList tyco_env [(tv,tv) | tv <- tycovars])
                    (extendVarEnvList id_env   [(id,id) | id <- ids])
  where (tycovars, ids) = partition isTyCoVar vars
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extendIdZonkEnv1 :: ZonkEnv -> Var -> ZonkEnv
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extendIdZonkEnv1 (ZonkEnv zonk_ty ty_env id_env) id
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  = ZonkEnv zonk_ty ty_env (extendVarEnv id_env id id)
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extendTyZonkEnv1 :: ZonkEnv -> TyVar -> ZonkEnv
extendTyZonkEnv1 (ZonkEnv zonk_ty ty_env id_env) ty
  = ZonkEnv zonk_ty (extendVarEnv ty_env ty ty) id_env

setZonkType :: ZonkEnv -> UnboundTyVarZonker -> ZonkEnv
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setZonkType (ZonkEnv _ ty_env id_env) zonk_ty
  = ZonkEnv zonk_ty ty_env id_env
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zonkEnvIds :: ZonkEnv -> TypeEnv
zonkEnvIds (ZonkEnv _ _ id_env) =
  mkNameEnv [(getName id, AnId id) | id <- nonDetEltsUFM id_env]
  -- It's OK to use nonDetEltsUFM here because we forget the ordering
  -- immediately by creating a TypeEnv
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zonkIdOcc :: ZonkEnv -> TcId -> Id
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-- Ids defined in this module should be in the envt;
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-- ignore others.  (Actually, data constructors are also
-- not LocalVars, even when locally defined, but that is fine.)
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-- (Also foreign-imported things aren't currently in the ZonkEnv;
--  that's ok because they don't need zonking.)
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--
-- Actually, Template Haskell works in 'chunks' of declarations, and
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-- an earlier chunk won't be in the 'env' that the zonking phase
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-- carries around.  Instead it'll be in the tcg_gbl_env, already fully
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-- zonked.  There's no point in looking it up there (except for error
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-- checking), and it's not conveniently to hand; hence the simple
-- 'orElse' case in the LocalVar branch.
--
-- Even without template splices, in module Main, the checking of
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-- 'main' is done as a separate chunk.
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zonkIdOcc (ZonkEnv _zonk_ty _ty_env id_env) id
  | isLocalVar id = lookupVarEnv id_env id `orElse`
                    id
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  | otherwise     = id
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zonkIdOccs :: ZonkEnv -> [TcId] -> [Id]
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zonkIdOccs env ids = map (zonkIdOcc env) ids
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-- zonkIdBndr is used *after* typechecking to get the Id's type
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-- to its final form.  The TyVarEnv give
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zonkIdBndr :: ZonkEnv -> TcId -> TcM Id
zonkIdBndr env id
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  = do ty' <- zonkTcTypeToType env (idType id)
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       ensureNotRepresentationPolymorphic ty'
         (text "In the type of binder" <+> quotes (ppr id))
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       return (setIdType id ty')
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zonkIdBndrs :: ZonkEnv -> [TcId] -> TcM [Id]
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zonkIdBndrs env ids = mapM (zonkIdBndr env) ids
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zonkTopBndrs :: [TcId] -> TcM [Id]
zonkTopBndrs ids = zonkIdBndrs emptyZonkEnv ids
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zonkFieldOcc :: ZonkEnv -> FieldOcc TcId -> TcM (FieldOcc Id)
zonkFieldOcc env (FieldOcc lbl sel) = fmap (FieldOcc lbl) $ zonkIdBndr env sel

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zonkEvBndrsX :: ZonkEnv -> [EvVar] -> TcM (ZonkEnv, [Var])
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zonkEvBndrsX = mapAccumLM zonkEvBndrX
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zonkEvBndrX :: ZonkEnv -> EvVar -> TcM (ZonkEnv, EvVar)
-- Works for dictionaries and coercions
zonkEvBndrX env var
  = do { var' <- zonkEvBndr env var
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       ; return (extendZonkEnv env [var'], var') }
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zonkEvBndr :: ZonkEnv -> EvVar -> TcM EvVar
-- Works for dictionaries and coercions
-- Does not extend the ZonkEnv
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zonkEvBndr env var
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  = do { let var_ty = varType var
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       ; ty <-
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           {-# SCC "zonkEvBndr_zonkTcTypeToType" #-}
           zonkTcTypeToType env var_ty
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       ; return (setVarType var ty) }
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zonkEvVarOcc :: ZonkEnv -> EvVar -> TcM EvTerm
zonkEvVarOcc env v
  | isCoVar v
  = EvCoercion <$> zonkCoVarOcc env v
  | otherwise
  = return (EvId $ zonkIdOcc env v)
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zonkTyBndrsX :: ZonkEnv -> [TyVar] -> TcM (ZonkEnv, [TyVar])
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zonkTyBndrsX = mapAccumLM zonkTyBndrX
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zonkTyBndrX :: ZonkEnv -> TyVar -> TcM (ZonkEnv, TyVar)
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-- This guarantees to return a TyVar (not a TcTyVar)
-- then we add it to the envt, so all occurrences are replaced
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zonkTyBndrX env tv
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  = ASSERT( isImmutableTyVar tv )
    do { ki <- zonkTcTypeToType env (tyVarKind tv)
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               -- Internal names tidy up better, for iface files.
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       ; let tv' = mkTyVar (tyVarName tv) ki
       ; return (extendTyZonkEnv1 env tv', tv') }
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zonkTyConBinders :: ZonkEnv -> [TyConBinder] -> TcM (ZonkEnv, [TyConBinder])
zonkTyConBinders = mapAccumLM zonkTyConBinderX
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zonkTyConBinderX :: ZonkEnv -> TyConBinder -> TcM (ZonkEnv, TyConBinder)
zonkTyConBinderX env (TvBndr tv vis)
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  = do { (env', tv') <- zonkTyBndrX env tv
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       ; return (env', TvBndr tv' vis) }
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zonkTopExpr :: HsExpr TcId -> TcM (HsExpr Id)
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zonkTopExpr e = zonkExpr emptyZonkEnv e

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zonkTopLExpr :: LHsExpr TcId -> TcM (LHsExpr Id)
zonkTopLExpr e = zonkLExpr emptyZonkEnv e

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zonkTopDecls :: Bag EvBind
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             -> LHsBinds TcId
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             -> [LRuleDecl TcId] -> [LVectDecl TcId] -> [LTcSpecPrag] -> [LForeignDecl TcId]
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             -> TcM (TypeEnv,
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                     Bag EvBind,
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                     LHsBinds Id,
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                     [LForeignDecl Id],
                     [LTcSpecPrag],
                     [LRuleDecl    Id],
                     [LVectDecl    Id])
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zonkTopDecls ev_binds binds rules vects imp_specs fords
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  = do  { (env1, ev_binds') <- zonkEvBinds emptyZonkEnv ev_binds
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        ; (env2, binds') <- zonkRecMonoBinds env1 binds
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                        -- Top level is implicitly recursive
        ; rules' <- zonkRules env2 rules
        ; vects' <- zonkVects env2 vects
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        ; specs' <- zonkLTcSpecPrags env2 imp_specs
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        ; fords' <- zonkForeignExports env2 fords
        ; return (zonkEnvIds env2, ev_binds', binds', fords', specs', rules', vects') }
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---------------------------------------------
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zonkLocalBinds :: ZonkEnv -> HsLocalBinds TcId -> TcM (ZonkEnv, HsLocalBinds Id)
zonkLocalBinds env EmptyLocalBinds
  = return (env, EmptyLocalBinds)

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zonkLocalBinds _ (HsValBinds (ValBindsIn {}))
  = panic "zonkLocalBinds" -- Not in typechecker output

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zonkLocalBinds env (HsValBinds (ValBindsOut binds sigs))
  = do  { (env1, new_binds) <- go env binds
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        ; return (env1, HsValBinds (ValBindsOut new_binds sigs)) }
  where
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    go env []
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      = return (env, [])
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    go env ((r,b):bs)
      = do { (env1, b')  <- zonkRecMonoBinds env b
           ; (env2, bs') <- go env1 bs
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           ; return (env2, (r,b'):bs') }
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zonkLocalBinds env (HsIPBinds (IPBinds binds dict_binds)) = do
    new_binds <- mapM (wrapLocM zonk_ip_bind) binds
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    let
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        env1 = extendIdZonkEnvRec env [ n | L _ (IPBind (Right n) _) <- new_binds]
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    (env2, new_dict_binds) <- zonkTcEvBinds env1 dict_binds
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    return (env2, HsIPBinds (IPBinds new_binds new_dict_binds))
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  where
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    zonk_ip_bind (IPBind n e)
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        = do n' <- mapIPNameTc (zonkIdBndr env) n
             e' <- zonkLExpr env e
             return (IPBind n' e')
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---------------------------------------------
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zonkRecMonoBinds :: ZonkEnv -> LHsBinds TcId -> TcM (ZonkEnv, LHsBinds Id)
zonkRecMonoBinds env binds
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 = fixM (\ ~(_, new_binds) -> do
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        { let env1 = extendIdZonkEnvRec env (collectHsBindsBinders new_binds)
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        ; binds' <- zonkMonoBinds env1 binds
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        ; return (env1, binds') })

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---------------------------------------------
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zonkMonoBinds :: ZonkEnv -> LHsBinds TcId -> TcM (LHsBinds Id)
zonkMonoBinds env binds = mapBagM (zonk_lbind env) binds
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zonk_lbind :: ZonkEnv -> LHsBind TcId -> TcM (LHsBind Id)
zonk_lbind env = wrapLocM (zonk_bind env)
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zonk_bind :: ZonkEnv -> HsBind TcId -> TcM (HsBind Id)
zonk_bind env bind@(PatBind { pat_lhs = pat, pat_rhs = grhss, pat_rhs_ty = ty})
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  = do  { (_env, new_pat) <- zonkPat env pat            -- Env already extended
        ; new_grhss <- zonkGRHSs env zonkLExpr grhss
        ; new_ty    <- zonkTcTypeToType env ty
        ; return (bind { pat_lhs = new_pat, pat_rhs = new_grhss, pat_rhs_ty = new_ty }) }
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zonk_bind env (VarBind { var_id = var, var_rhs = expr, var_inline = inl })
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  = do { new_var  <- zonkIdBndr env var
       ; new_expr <- zonkLExpr env expr
       ; return (VarBind { var_id = new_var, var_rhs = new_expr, var_inline = inl }) }

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zonk_bind env bind@(FunBind { fun_id = L loc var, fun_matches = ms
                            , fun_co_fn = co_fn })
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  = do { new_var <- zonkIdBndr env var
       ; (env1, new_co_fn) <- zonkCoFn env co_fn
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       ; new_ms <- zonkMatchGroup env1 zonkLExpr ms
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       ; return (bind { fun_id = L loc new_var, fun_matches = new_ms
                      , fun_co_fn = new_co_fn }) }

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zonk_bind env (AbsBinds { abs_tvs = tyvars, abs_ev_vars = evs
                        , abs_ev_binds = ev_binds
                        , abs_exports = exports
                        , abs_binds = val_binds })
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  = ASSERT( all isImmutableTyVar tyvars )
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    do { (env0, new_tyvars) <- zonkTyBndrsX env tyvars
       ; (env1, new_evs) <- zonkEvBndrsX env0 evs
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       ; (env2, new_ev_binds) <- zonkTcEvBinds_s env1 ev_binds
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       ; (new_val_bind, new_exports) <- fixM $ \ ~(new_val_binds, _) ->
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         do { let env3 = extendIdZonkEnvRec env2
                           (collectHsBindsBinders new_val_binds)
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            ; new_val_binds <- zonkMonoBinds env3 val_binds
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            ; new_exports   <- mapM (zonkExport env3) exports
            ; return (new_val_binds, new_exports) }
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       ; return (AbsBinds { abs_tvs = new_tyvars, abs_ev_vars = new_evs
                          , abs_ev_binds = new_ev_binds
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                          , abs_exports = new_exports, abs_binds = new_val_bind }) }
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  where
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    zonkExport env (ABE{ abe_wrap = wrap
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                       , abe_poly = poly_id
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                       , abe_mono = mono_id, abe_prags = prags })
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        = do new_poly_id <- zonkIdBndr env poly_id
             (_, new_wrap) <- zonkCoFn env wrap
             new_prags <- zonkSpecPrags env prags
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             return (ABE{ abe_wrap = new_wrap
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                        , abe_poly = new_poly_id
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                        , abe_mono = zonkIdOcc env mono_id
                        , abe_prags = new_prags })
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zonk_bind env outer_bind@(AbsBindsSig { abs_tvs         = tyvars
                                      , abs_ev_vars     = evs
                                      , abs_sig_export  = poly
                                      , abs_sig_prags   = prags
                                      , abs_sig_ev_bind = ev_bind
                                      , abs_sig_bind    = lbind })
  | L bind_loc bind@(FunBind { fun_id      = L loc local
                             , fun_matches = ms
                             , fun_co_fn   = co_fn }) <- lbind
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  = ASSERT( all isImmutableTyVar tyvars )
    do { (env0, new_tyvars)  <- zonkTyBndrsX env  tyvars
       ; (env1, new_evs)     <- zonkEvBndrsX env0 evs
       ; (env2, new_ev_bind) <- zonkTcEvBinds env1 ev_bind
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           -- Inline zonk_bind (FunBind ...) because we wish to skip
           -- the check for representation-polymorphic binders. The
           -- local binder in the FunBind in an AbsBindsSig is never actually
           -- bound in Core -- indeed, that's the whole point of AbsBindsSig.
           -- just calling zonk_bind causes #11405.
       ; new_local           <- updateVarTypeM (zonkTcTypeToType env2) local
       ; (env3, new_co_fn)   <- zonkCoFn env2 co_fn
       ; new_ms              <- zonkMatchGroup env3 zonkLExpr ms
           -- If there is a representation polymorphism problem, it will
           -- be caught here:
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       ; new_poly_id         <- zonkIdBndr env2 poly
       ; new_prags           <- zonkSpecPrags env2 prags
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       ; let new_val_bind = L bind_loc (bind { fun_id      = L loc new_local
                                             , fun_matches = new_ms
                                             , fun_co_fn   = new_co_fn })
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       ; return (AbsBindsSig { abs_tvs         = new_tyvars
                             , abs_ev_vars     = new_evs
                             , abs_sig_export  = new_poly_id
                             , abs_sig_prags   = new_prags
                             , abs_sig_ev_bind = new_ev_bind
                             , abs_sig_bind    = new_val_bind  }) }

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  | otherwise
  = pprPanic "zonk_bind" (ppr outer_bind)

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zonk_bind env (PatSynBind bind@(PSB { psb_id = L loc id
                                    , psb_args = details
                                    , psb_def = lpat
                                    , psb_dir = dir }))
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  = do { id' <- zonkIdBndr env id
       ; details' <- zonkPatSynDetails env details
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       ; (env1, lpat') <- zonkPat env lpat
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       ; (_env2, dir') <- zonkPatSynDir env1 dir
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       ; return $ PatSynBind $
                  bind { psb_id = L loc id'
                       , psb_args = details'
                       , psb_def = lpat'
                       , psb_dir = dir' } }
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zonkPatSynDetails :: ZonkEnv
                  -> HsPatSynDetails (Located TcId)
                  -> TcM (HsPatSynDetails (Located Id))
zonkPatSynDetails env = traverse (wrapLocM $ zonkIdBndr env)

zonkPatSynDir :: ZonkEnv -> HsPatSynDir TcId -> TcM (ZonkEnv, HsPatSynDir Id)
zonkPatSynDir env Unidirectional = return (env, Unidirectional)
zonkPatSynDir env ImplicitBidirectional = return (env, ImplicitBidirectional)
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zonkPatSynDir env (ExplicitBidirectional mg) = do
    mg' <- zonkMatchGroup env zonkLExpr mg
    return (env, ExplicitBidirectional mg')
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zonkSpecPrags :: ZonkEnv -> TcSpecPrags -> TcM TcSpecPrags
zonkSpecPrags _   IsDefaultMethod = return IsDefaultMethod
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zonkSpecPrags env (SpecPrags ps)  = do { ps' <- zonkLTcSpecPrags env ps
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                                       ; return (SpecPrags ps') }
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zonkLTcSpecPrags :: ZonkEnv -> [LTcSpecPrag] -> TcM [LTcSpecPrag]
zonkLTcSpecPrags env ps
  = mapM zonk_prag ps
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  where
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    zonk_prag (L loc (SpecPrag id co_fn inl))
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        = do { (_, co_fn') <- zonkCoFn env co_fn
             ; return (L loc (SpecPrag (zonkIdOcc env id) co_fn' inl)) }
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{-
************************************************************************
*                                                                      *
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\subsection[BackSubst-Match-GRHSs]{Match and GRHSs}
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*                                                                      *
************************************************************************
-}
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zonkMatchGroup :: ZonkEnv
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               -> (ZonkEnv -> Located (body TcId) -> TcM (Located (body Id)))
               -> MatchGroup TcId (Located (body TcId)) -> TcM (MatchGroup Id (Located (body Id)))
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zonkMatchGroup env zBody (MG { mg_alts = L l ms, mg_arg_tys = arg_tys
                             , mg_res_ty = res_ty, mg_origin = origin })
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  = do  { ms' <- mapM (zonkMatch env zBody) ms
        ; arg_tys' <- zonkTcTypeToTypes env arg_tys
        ; res_ty'  <- zonkTcTypeToType env res_ty
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        ; return (MG { mg_alts = L l ms', mg_arg_tys = arg_tys'
                     , mg_res_ty = res_ty', mg_origin = origin }) }
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zonkMatch :: ZonkEnv
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          -> (ZonkEnv -> Located (body TcId) -> TcM (Located (body Id)))
          -> LMatch TcId (Located (body TcId)) -> TcM (LMatch Id (Located (body Id)))
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zonkMatch env zBody (L loc (Match mf pats _ grhss))
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  = do  { (env1, new_pats) <- zonkPats env pats
        ; new_grhss <- zonkGRHSs env1 zBody grhss
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        ; return (L loc (Match mf new_pats Nothing new_grhss)) }
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-------------------------------------------------------------------------
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zonkGRHSs :: ZonkEnv
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          -> (ZonkEnv -> Located (body TcId) -> TcM (Located (body Id)))
          -> GRHSs TcId (Located (body TcId)) -> TcM (GRHSs Id (Located (body Id)))
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zonkGRHSs env zBody (GRHSs grhss (L l binds)) = do
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    (new_env, new_binds) <- zonkLocalBinds env binds
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    let
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        zonk_grhs (GRHS guarded rhs)
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          = do (env2, new_guarded) <- zonkStmts new_env zonkLExpr guarded
               new_rhs <- zBody env2 rhs
               return (GRHS new_guarded new_rhs)
    new_grhss <- mapM (wrapLocM zonk_grhs) grhss
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    return (GRHSs new_grhss (L l new_binds))
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{-
************************************************************************
*                                                                      *
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\subsection[BackSubst-HsExpr]{Running a zonkitution over a TypeCheckedExpr}
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*                                                                      *
************************************************************************
-}
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zonkLExprs :: ZonkEnv -> [LHsExpr TcId] -> TcM [LHsExpr Id]
zonkLExpr  :: ZonkEnv -> LHsExpr TcId   -> TcM (LHsExpr Id)
zonkExpr   :: ZonkEnv -> HsExpr TcId    -> TcM (HsExpr Id)
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zonkLExprs env exprs = mapM (zonkLExpr env) exprs
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zonkLExpr  env expr  = wrapLocM (zonkExpr env) expr
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zonkExpr env (HsVar (L l id))
  = return (HsVar (L l (zonkIdOcc env id)))
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zonkExpr _ (HsIPVar id)
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  = return (HsIPVar id)
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zonkExpr _ (HsOverLabel l)
  = return (HsOverLabel l)

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zonkExpr env (HsLit (HsRat f ty))
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  = do new_ty <- zonkTcTypeToType env ty
       return (HsLit (HsRat f new_ty))
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zonkExpr _ (HsLit lit)
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  = return (HsLit lit)
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zonkExpr env (HsOverLit lit)
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  = do  { lit' <- zonkOverLit env lit
        ; return (HsOverLit lit') }
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zonkExpr env (HsLam matches)
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  = do new_matches <- zonkMatchGroup env zonkLExpr matches
       return (HsLam new_matches)
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zonkExpr env (HsLamCase matches)
  = do new_matches <- zonkMatchGroup env zonkLExpr matches
       return (HsLamCase new_matches)
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zonkExpr env (HsApp e1 e2)
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  = do new_e1 <- zonkLExpr env e1
       new_e2 <- zonkLExpr env e2
       return (HsApp new_e1 new_e2)
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zonkExpr env (HsAppTypeOut e t)
  = do new_e <- zonkLExpr env e
       return (HsAppTypeOut new_e t)
       -- NB: the type is an HsType; can't zonk that!

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zonkExpr _ e@(HsRnBracketOut _ _)
  = pprPanic "zonkExpr: HsRnBracketOut" (ppr e)

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zonkExpr env (HsTcBracketOut body bs)
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  = do bs' <- mapM zonk_b bs
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       return (HsTcBracketOut body bs')
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  where
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    zonk_b (PendingTcSplice n e) = do e' <- zonkLExpr env e
                                      return (PendingTcSplice n e')
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zonkExpr _ (HsSpliceE s) = WARN( True, ppr s ) -- Should not happen
                           return (HsSpliceE s)
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zonkExpr env (OpApp e1 op fixity e2)
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  = do new_e1 <- zonkLExpr env e1
       new_op <- zonkLExpr env op
       new_e2 <- zonkLExpr env e2
       return (OpApp new_e1 new_op fixity new_e2)
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zonkExpr env (NegApp expr op)
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  = do (env', new_op) <- zonkSyntaxExpr env op
       new_expr <- zonkLExpr env' expr
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       return (NegApp new_expr new_op)
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zonkExpr env (HsPar e)
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  = do new_e <- zonkLExpr env e
       return (HsPar new_e)
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zonkExpr env (SectionL expr op)
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  = do new_expr <- zonkLExpr env expr
       new_op   <- zonkLExpr env op
       return (SectionL new_expr new_op)
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zonkExpr env (SectionR op expr)
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  = do new_op   <- zonkLExpr env op
       new_expr <- zonkLExpr env expr
       return (SectionR new_op new_expr)
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zonkExpr env (ExplicitTuple tup_args boxed)
  = do { new_tup_args <- mapM zonk_tup_arg tup_args
       ; return (ExplicitTuple new_tup_args boxed) }
  where
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    zonk_tup_arg (L l (Present e)) = do { e' <- zonkLExpr env e
                                        ; return (L l (Present e')) }
    zonk_tup_arg (L l (Missing t)) = do { t' <- zonkTcTypeToType env t
                                        ; return (L l (Missing t')) }
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zonkExpr env (HsCase expr ms)
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  = do new_expr <- zonkLExpr env expr
       new_ms <- zonkMatchGroup env zonkLExpr ms
       return (HsCase new_expr new_ms)
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zonkExpr env (HsIf Nothing e1 e2 e3)
  = do new_e1 <- zonkLExpr env e1
       new_e2 <- zonkLExpr env e2
       new_e3 <- zonkLExpr env e3
       return (HsIf Nothing new_e1 new_e2 new_e3)

zonkExpr env (HsIf (Just fun) e1 e2 e3)
  = do (env1, new_fun) <- zonkSyntaxExpr env fun
       new_e1 <- zonkLExpr env1 e1
       new_e2 <- zonkLExpr env1 e2
       new_e3 <- zonkLExpr env1 e3
       return (HsIf (Just new_fun) new_e1 new_e2 new_e3)
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zonkExpr env (HsMultiIf ty alts)
  = do { alts' <- mapM (wrapLocM zonk_alt) alts
       ; ty'   <- zonkTcTypeToType env ty
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       ; return $ HsMultiIf ty' alts' }
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  where zonk_alt (GRHS guard expr)
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          = do { (env', guard') <- zonkStmts env zonkLExpr guard
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               ; expr'          <- zonkLExpr env' expr
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               ; return $ GRHS guard' expr' }
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zonkExpr env (HsLet (L l binds) expr)
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  = do (new_env, new_binds) <- zonkLocalBinds env binds
       new_expr <- zonkLExpr new_env expr
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       return (HsLet (L l new_binds) new_expr)
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zonkExpr env (HsDo do_or_lc (L l stmts) ty)
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  = do (_, new_stmts) <- zonkStmts env zonkLExpr stmts
       new_ty <- zonkTcTypeToType env ty
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       return (HsDo do_or_lc (L l new_stmts) new_ty)
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zonkExpr env (ExplicitList ty wit exprs)
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  = do (env1, new_wit) <- zonkWit env wit
       new_ty <- zonkTcTypeToType env1 ty
       new_exprs <- zonkLExprs env1 exprs
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       return (ExplicitList new_ty new_wit new_exprs)
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   where zonkWit env Nothing    = return (env, Nothing)
         zonkWit env (Just fln) = second Just <$> zonkSyntaxExpr env fln
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zonkExpr env (ExplicitPArr ty exprs)
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  = do new_ty <- zonkTcTypeToType env ty
       new_exprs <- zonkLExprs env exprs
       return (ExplicitPArr new_ty new_exprs)
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zonkExpr env expr@(RecordCon { rcon_con_expr = con_expr, rcon_flds = rbinds })
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  = do  { new_con_expr <- zonkExpr env con_expr
        ; new_rbinds   <- zonkRecFields env rbinds
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        ; return (expr { rcon_con_expr = new_con_expr
                       , rcon_flds = new_rbinds }) }
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zonkExpr env (RecordUpd { rupd_expr = expr, rupd_flds = rbinds
                        , rupd_cons = cons, rupd_in_tys = in_tys
                        , rupd_out_tys = out_tys, rupd_wrap = req_wrap })
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  = do  { new_expr    <- zonkLExpr env expr
        ; new_in_tys  <- mapM (zonkTcTypeToType env) in_tys
        ; new_out_tys <- mapM (zonkTcTypeToType env) out_tys
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        ; new_rbinds  <- zonkRecUpdFields env rbinds
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        ; (_, new_recwrap) <- zonkCoFn env req_wrap
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        ; return (RecordUpd { rupd_expr = new_expr, rupd_flds =  new_rbinds
                            , rupd_cons = cons, rupd_in_tys = new_in_tys
                            , rupd_out_tys = new_out_tys, rupd_wrap = new_recwrap }) }
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zonkExpr env (ExprWithTySigOut e ty)
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  = do { e' <- zonkLExpr env e
       ; return (ExprWithTySigOut e' ty) }

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zonkExpr env (ArithSeq expr wit info)
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  = do (env1, new_wit) <- zonkWit env wit
       new_expr <- zonkExpr env expr
       new_info <- zonkArithSeq env1 info
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       return (ArithSeq new_expr new_wit new_info)
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   where zonkWit env Nothing    = return (env, Nothing)
         zonkWit env (Just fln) = second Just <$> zonkSyntaxExpr env fln
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zonkExpr env (PArrSeq expr info)
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  = do new_expr <- zonkExpr env expr
       new_info <- zonkArithSeq env info
       return (PArrSeq new_expr new_info)
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zonkExpr env (HsSCC src lbl expr)
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  = do new_expr <- zonkLExpr env expr
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       return (HsSCC src lbl new_expr)
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zonkExpr env (HsTickPragma src info srcInfo expr)
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  = do new_expr <- zonkLExpr env expr
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       return (HsTickPragma src info srcInfo new_expr)
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-- hdaume: core annotations
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zonkExpr env (HsCoreAnn src lbl expr)
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  = do new_expr <- zonkLExpr env expr
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       return (HsCoreAnn src lbl new_expr)
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-- arrow notation extensions
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zonkExpr env (HsProc pat body)
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  = do  { (env1, new_pat) <- zonkPat env pat
        ; new_body <- zonkCmdTop env1 body
        ; return (HsProc new_pat new_body) }
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-- StaticPointers extension
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zonkExpr env (HsStatic fvs expr)
  = HsStatic fvs <$> zonkLExpr env expr
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zonkExpr env (HsWrap co_fn expr)
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  = do (env1, new_co_fn) <- zonkCoFn env co_fn
       new_expr <- zonkExpr env1 expr
       return (HsWrap new_co_fn new_expr)
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zonkExpr _ e@(HsUnboundVar {}) = return e
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zonkExpr _ expr = pprPanic "zonkExpr" (ppr expr)
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-------------------------------------------------------------------------
{-
Note [Skolems in zonkSyntaxExpr]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider rebindable syntax with something like

  (>>=) :: (forall x. blah) -> (forall y. blah') -> blah''

The x and y become skolems that are in scope when type-checking the
arguments to the bind. This means that we must extend the ZonkEnv with
these skolems when zonking the arguments to the bind. But the skolems
are different between the two arguments, and so we should theoretically
carry around different environments to use for the different arguments.

However, this becomes a logistical nightmare, especially in dealing with
the more exotic Stmt forms. So, we simplify by making the critical
assumption that the uniques of the skolems are different. (This assumption
is justified by the use of newUnique in TcMType.instSkolTyCoVarX.)
Now, we can safely just extend one environment.
-}

-- See Note [Skolems in zonkSyntaxExpr]
zonkSyntaxExpr :: ZonkEnv -> SyntaxExpr TcId
               -> TcM (ZonkEnv, SyntaxExpr Id)
zonkSyntaxExpr env (SyntaxExpr { syn_expr      = expr
                               , syn_arg_wraps = arg_wraps
                               , syn_res_wrap  = res_wrap })
  = do { (env0, res_wrap')  <- zonkCoFn env res_wrap
       ; expr'              <- zonkExpr env0 expr
       ; (env1, arg_wraps') <- mapAccumLM zonkCoFn env0 arg_wraps
       ; return (env1, SyntaxExpr { syn_expr      = expr'
                                  , syn_arg_wraps = arg_wraps'
                                  , syn_res_wrap  = res_wrap' }) }

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

zonkLCmd  :: ZonkEnv -> LHsCmd TcId   -> TcM (LHsCmd Id)
zonkCmd   :: ZonkEnv -> HsCmd TcId    -> TcM (HsCmd Id)

zonkLCmd  env cmd  = wrapLocM (zonkCmd env) cmd

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zonkCmd env (HsCmdWrap w cmd)
  = do { (env1, w') <- zonkCoFn env w
       ; cmd' <- zonkCmd env1 cmd
       ; return (HsCmdWrap w' cmd') }
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zonkCmd env (HsCmdArrApp e1 e2 ty ho rl)
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  = do new_e1 <- zonkLExpr env e1
       new_e2 <- zonkLExpr env e2
       new_ty <- zonkTcTypeToType env ty
       return (HsCmdArrApp new_e1 new_e2 new_ty ho rl)
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zonkCmd env (HsCmdArrForm op fixity args)
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  = do new_op <- zonkLExpr env op
       new_args <- mapM (zonkCmdTop env) args
       return (HsCmdArrForm new_op fixity new_args)
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zonkCmd env (HsCmdApp c e)
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  = do new_c <- zonkLCmd env c
       new_e <- zonkLExpr env e
       return (HsCmdApp new_c new_e)
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zonkCmd env (HsCmdLam matches)
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  = do new_matches <- zonkMatchGroup env zonkLCmd matches
       return (HsCmdLam new_matches)
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zonkCmd env (HsCmdPar c)
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  = do new_c <- zonkLCmd env c
       return (HsCmdPar new_c)
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zonkCmd env (HsCmdCase expr ms)
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  = do new_expr <- zonkLExpr env expr
       new_ms <- zonkMatchGroup env zonkLCmd ms
       return (HsCmdCase new_expr new_ms)
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zonkCmd env (HsCmdIf eCond ePred cThen cElse)
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  = do { (env1, new_eCond) <- zonkWit env eCond
       ; new_ePred <- zonkLExpr env1 ePred
       ; new_cThen <- zonkLCmd env1 cThen
       ; new_cElse <- zonkLCmd env1 cElse
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       ; return (HsCmdIf new_eCond new_ePred new_cThen new_cElse) }
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  where
    zonkWit env Nothing  = return (env, Nothing)
    zonkWit env (Just w) = second Just <$> zonkSyntaxExpr env w
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zonkCmd env (HsCmdLet (L l binds) cmd)
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  = do (new_env, new_binds) <- zonkLocalBinds env binds
       new_cmd <- zonkLCmd new_env cmd
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       return (HsCmdLet (L l new_binds) new_cmd)
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zonkCmd env (HsCmdDo (L l stmts) ty)
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  = do (_, new_stmts) <- zonkStmts env zonkLCmd stmts
       new_ty <- zonkTcTypeToType env ty
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       return (HsCmdDo (L l new_stmts) new_ty)
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zonkCmdTop :: ZonkEnv -> LHsCmdTop TcId -> TcM (LHsCmdTop Id)
zonkCmdTop env cmd = wrapLocM (zonk_cmd_top env) cmd

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zonk_cmd_top :: ZonkEnv -> HsCmdTop TcId -> TcM (HsC