    {-
    (c) The University of Glasgow 2006
    (c) The GRASP/AQUA Project, Glasgow University, 1992-1998

    \section[Id]{@Ids@: Value and constructor identifiers}
    -}

    {-# LANGUAGE CPP #-}

    -- |
    -- #name_types#
    -- GHC uses several kinds of name internally:
    --
    -- * 'OccName.OccName': see "OccName#name_types"
    --
    -- * 'RdrName.RdrName': see "RdrName#name_types"
    --
    -- * 'Name.Name': see "Name#name_types"
    --
    -- * 'Id.Id' represents names that not only have a 'Name.Name' but also a 'TypeRep.Type' and some additional
    --   details (a 'IdInfo.IdInfo' and one of 'Var.LocalIdDetails' or 'IdInfo.GlobalIdDetails') that
    --   are added, modified and inspected by various compiler passes. These 'Var.Var' names may either
    --   be global or local, see "Var#globalvslocal"
    --
    -- * 'Var.Var': see "Var#name_types"

    module Id (
            -- * The main types
            Var, Id, isId,

            -- ** Simple construction
            mkGlobalId, mkVanillaGlobal, mkVanillaGlobalWithInfo,
            mkLocalId, mkLocalIdWithInfo, mkExportedLocalId,
            mkSysLocal, mkSysLocalM, mkUserLocal, mkUserLocalM,
            mkDerivedLocalM,
            mkTemplateLocals, mkTemplateLocalsNum, mkTemplateLocal,
            mkWorkerId, mkWiredInIdName,

            -- ** Taking an Id apart
            idName, idType, idUnique, idInfo, idDetails, idRepArity,
            recordSelectorFieldLabel,

            -- ** Modifying an Id
            setIdName, setIdUnique, Id.setIdType,
            setIdExported, setIdNotExported,
            globaliseId, localiseId,
            setIdInfo, lazySetIdInfo, modifyIdInfo, maybeModifyIdInfo,
            zapLamIdInfo, zapIdDemandInfo, zapIdUsageInfo, zapFragileIdInfo,
            zapIdStrictness,
            transferPolyIdInfo,

            -- ** Predicates on Ids
            isImplicitId, isDeadBinder,
            isStrictId,
            isExportedId, isLocalId, isGlobalId,
            isRecordSelector, isNaughtyRecordSelector,
            isClassOpId_maybe, isDFunId,
            isPrimOpId, isPrimOpId_maybe,
            isFCallId, isFCallId_maybe,
            isDataConWorkId, isDataConWorkId_maybe, isDataConId_maybe, idDataCon,
            isConLikeId, isBottomingId, idIsFrom,
            hasNoBinding,

            -- ** Evidence variables
            DictId, isDictId, dfunNSilent, isEvVar,

            -- ** Inline pragma stuff
            idInlinePragma, setInlinePragma, modifyInlinePragma,
            idInlineActivation, setInlineActivation, idRuleMatchInfo,

            -- ** One-shot lambdas
            isOneShotBndr, isOneShotLambda, isProbablyOneShotLambda,
            setOneShotLambda, clearOneShotLambda,
            updOneShotInfo, setIdOneShotInfo,
            isStateHackType, stateHackOneShot, typeOneShot,

            -- ** Reading 'IdInfo' fields
            idArity,
            idCallArity,
            idUnfolding, realIdUnfolding,
            idSpecialisation, idCoreRules, idHasRules,
            idCafInfo,
            idOneShotInfo,
            idOccInfo,

            -- ** Writing 'IdInfo' fields
            setIdUnfoldingLazily,
            setIdUnfolding,
            setIdArity,
            setIdCallArity,

            setIdSpecialisation,
            setIdCafInfo,
            setIdOccInfo, zapIdOccInfo,

            setIdDemandInfo,
            setIdStrictness,

            idDemandInfo,
            idStrictness,

        ) where

    #include "HsVersions.h"

    import CoreSyn ( CoreRule, Unfolding( NoUnfolding ) )

    import IdInfo
    import BasicTypes

    -- Imported and re-exported
    import Var( Id, DictId,
                idInfo, idDetails, globaliseId, varType,
                isId, isLocalId, isGlobalId, isExportedId )
    import qualified Var

    import TyCon
    import Type
    import TysPrim
    import DataCon
    import Demand
    import Name
    import Module
    import Class
    import {-# SOURCE #-} PrimOp (PrimOp)
    import ForeignCall
    import Maybes
    import SrcLoc
    import Outputable
    import Unique
    import UniqSupply
    import FastString
    import Util
    import StaticFlags

    -- infixl so you can say (id `set` a `set` b)
    infixl  1 `setIdUnfoldingLazily`,
              `setIdUnfolding`,
              `setIdArity`,
              `setIdCallArity`,
              `setIdOccInfo`,
              `setIdOneShotInfo`,

              `setIdSpecialisation`,
              `setInlinePragma`,
              `setInlineActivation`,
              `idCafInfo`,

              `setIdDemandInfo`,
              `setIdStrictness`

    {-
    ************************************************************************
    *                                                                      *
    \subsection{Basic Id manipulation}
    *                                                                      *
    ************************************************************************
    -}

    idName   :: Id -> Name
    idName    = Var.varName

    idUnique :: Id -> Unique
    idUnique  = Var.varUnique

    idType   :: Id -> Kind
    idType    = Var.varType

    setIdName :: Id -> Name -> Id
    setIdName = Var.setVarName

    setIdUnique :: Id -> Unique -> Id
    setIdUnique = Var.setVarUnique

    -- | Not only does this set the 'Id' 'Type', it also evaluates the type to try and
    -- reduce space usage
    setIdType :: Id -> Type -> Id
    setIdType id ty = seqType ty `seq` Var.setVarType id ty

    setIdExported :: Id -> Id
    setIdExported = Var.setIdExported

    setIdNotExported :: Id -> Id
    setIdNotExported = Var.setIdNotExported

    localiseId :: Id -> Id
    -- Make an with the same unique and type as the
    -- incoming Id, but with an *Internal* Name and *LocalId* flavour
    localiseId id
      | ASSERT( isId id ) isLocalId id && isInternalName name
      = id
      | otherwise
      = mkLocalIdWithInfo (localiseName name) (idType id) (idInfo id)
      where
        name = idName id

    lazySetIdInfo :: Id -> IdInfo -> Id
    lazySetIdInfo = Var.lazySetIdInfo

    setIdInfo :: Id -> IdInfo -> Id
    setIdInfo id info = seqIdInfo info `seq` (lazySetIdInfo id info)
            -- Try to avoid spack leaks by seq'ing

    modifyIdInfo :: (IdInfo -> IdInfo) -> Id -> Id
    modifyIdInfo fn id = setIdInfo id (fn (idInfo id))

    -- maybeModifyIdInfo tries to avoid unnecesary thrashing
    maybeModifyIdInfo :: Maybe IdInfo -> Id -> Id
    maybeModifyIdInfo (Just new_info) id = lazySetIdInfo id new_info
    maybeModifyIdInfo Nothing         id = id

    {-
    ************************************************************************
    *                                                                      *
    \subsection{Simple Id construction}
    *                                                                      *
    ************************************************************************

    Absolutely all Ids are made by mkId.  It is just like Var.mkId,
    but in addition it pins free-tyvar-info onto the Id's type,
    where it can easily be found.

    Note [Free type variables]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~
    At one time we cached the free type variables of the type of an Id
    at the root of the type in a TyNote.  The idea was to avoid repeating
    the free-type-variable calculation.  But it turned out to slow down
    the compiler overall. I don't quite know why; perhaps finding free
    type variables of an Id isn't all that common whereas applying a
    substitution (which changes the free type variables) is more common.
    Anyway, we removed it in March 2008.
    -}

    -- | For an explanation of global vs. local 'Id's, see "Var#globalvslocal"
    mkGlobalId :: IdDetails -> Name -> Type -> IdInfo -> Id
    mkGlobalId = Var.mkGlobalVar

    -- | Make a global 'Id' without any extra information at all
    mkVanillaGlobal :: Name -> Type -> Id
    mkVanillaGlobal name ty = mkVanillaGlobalWithInfo name ty vanillaIdInfo

    -- | Make a global 'Id' with no global information but some generic 'IdInfo'
    mkVanillaGlobalWithInfo :: Name -> Type -> IdInfo -> Id
    mkVanillaGlobalWithInfo = mkGlobalId VanillaId

    -- | For an explanation of global vs. local 'Id's, see "Var#globalvslocal"
    mkLocalId :: Name -> Type -> Id
    mkLocalId name ty = mkLocalIdWithInfo name ty
                             (vanillaIdInfo `setOneShotInfo` typeOneShot ty)

    mkLocalIdWithInfo :: Name -> Type -> IdInfo -> Id
    mkLocalIdWithInfo name ty info = Var.mkLocalVar VanillaId name ty info
            -- Note [Free type variables]

    -- | Create a local 'Id' that is marked as exported.
    -- This prevents things attached to it from being removed as dead code.
    -- See Note [Exported LocalIds]
    mkExportedLocalId :: IdDetails -> Name -> Type -> Id
    mkExportedLocalId details name ty = Var.mkExportedLocalVar details name ty vanillaIdInfo
            -- Note [Free type variables]

    -- | Create a system local 'Id'. These are local 'Id's (see "Var#globalvslocal")
    -- that are created by the compiler out of thin air
    mkSysLocal :: FastString -> Unique -> Type -> Id
    mkSysLocal fs uniq ty = mkLocalId (mkSystemVarName uniq fs) ty

    mkSysLocalM :: MonadUnique m => FastString -> Type -> m Id
    mkSysLocalM fs ty = getUniqueM >>= (\uniq -> return (mkSysLocal fs uniq ty))

    -- | Create a user local 'Id'. These are local 'Id's (see "Var#globalvslocal") with a name and location that the user might recognize
    mkUserLocal :: OccName -> Unique -> Type -> SrcSpan -> Id
    mkUserLocal occ uniq ty loc = mkLocalId (mkInternalName uniq occ loc) ty

    mkUserLocalM :: MonadUnique m => OccName -> Type -> SrcSpan -> m Id
    mkUserLocalM occ ty loc = getUniqueM >>= (\uniq -> return (mkUserLocal occ uniq ty loc))

    mkDerivedLocalM :: MonadUnique m => (OccName -> OccName) -> Id -> Type -> m Id
    mkDerivedLocalM deriv_name id ty
        = getUniqueM >>= (\uniq -> return (mkLocalId (mkDerivedInternalName deriv_name uniq (getName id)) ty))

    mkWiredInIdName :: Module -> FastString -> Unique -> Id -> Name
    mkWiredInIdName mod fs uniq id
     = mkWiredInName mod (mkOccNameFS varName fs) uniq (AnId id) UserSyntax

    {-
    Make some local @Ids@ for a template @CoreExpr@.  These have bogus
    @Uniques@, but that's OK because the templates are supposed to be
    instantiated before use.
    -}

    -- | Workers get local names. "CoreTidy" will externalise these if necessary
    mkWorkerId :: Unique -> Id -> Type -> Id
    mkWorkerId uniq unwrkr ty
      = mkLocalId (mkDerivedInternalName mkWorkerOcc uniq (getName unwrkr)) ty

    -- | Create a /template local/: a family of system local 'Id's in bijection with @Int@s, typically used in unfoldings
    mkTemplateLocal :: Int -> Type -> Id
    mkTemplateLocal i ty = mkSysLocal (fsLit "tpl") (mkBuiltinUnique i) ty

    -- | Create a template local for a series of types
    mkTemplateLocals :: [Type] -> [Id]
    mkTemplateLocals = mkTemplateLocalsNum 1

    -- | Create a template local for a series of type, but start from a specified template local
    mkTemplateLocalsNum :: Int -> [Type] -> [Id]
    mkTemplateLocalsNum n tys = zipWith mkTemplateLocal [n..] tys

    {-
    Note [Exported LocalIds]
    ~~~~~~~~~~~~~~~~~~~~~~~~
    We use mkExportedLocalId for things like
     - Dictionary functions (DFunId)
     - Wrapper and matcher Ids for pattern synonyms
     - Default methods for classes
     - Pattern-synonym matcher and builder Ids
     - etc

    They marked as "exported" in the sense that they should be kept alive
    even if apparently unused in other bindings, and not dropped as dead
    code by the occurrence analyser.  (But "exported" here does not mean
    "brought into lexical scope by an import declaration". Indeed these
    things are always internal Ids that the user never sees.)

    It's very important that they are *LocalIds*, not GlobalIs, for lots
    of reasons:

     * We want to treat them as free variables for the purpose of
       dependency analysis (e.g. CoreFVs.exprFreeVars).

     * Look them up in the current substitution when we come across
       occurrences of them (in Subst.lookupIdSubst). Lacking this we
       can get an out-of-date unfolding, which can in turn make the
       simplifier go into an infinite loop (Trac #9857)

     * Ensure that for dfuns that the specialiser does not float dict uses
       above their defns, which would prevent good simplifications happening.

     * The strictness analyser treats a occurrence of a GlobalId as
       imported and assumes it contains strictness in its IdInfo, which
       isn't true if the thing is bound in the same module as the
       occurrence.

    In CoreTidy we must make all these LocalIds into GlobalIds, so that in
    importing modules (in --make mode) we treat them as properly global.
    That is what is happening in, say tidy_insts in TidyPgm.

    ************************************************************************
    *                                                                      *
    \subsection{Special Ids}
    *                                                                      *
    ************************************************************************
    -}

    -- | If the 'Id' is that for a record selector, extract the 'sel_tycon' and label. Panic otherwise
    recordSelectorFieldLabel :: Id -> (TyCon, FieldLabel)
    recordSelectorFieldLabel id
      = case Var.idDetails id of
            RecSelId { sel_tycon = tycon } -> (tycon, idName id)
            _ -> panic "recordSelectorFieldLabel"

    isRecordSelector        :: Id -> Bool
    isNaughtyRecordSelector :: Id -> Bool
    isPrimOpId              :: Id -> Bool
    isFCallId               :: Id -> Bool
    isDataConWorkId         :: Id -> Bool
    isDFunId                :: Id -> Bool

    isClassOpId_maybe       :: Id -> Maybe Class
    isPrimOpId_maybe        :: Id -> Maybe PrimOp
    isFCallId_maybe         :: Id -> Maybe ForeignCall
    isDataConWorkId_maybe   :: Id -> Maybe DataCon

    isRecordSelector id = case Var.idDetails id of
                            RecSelId {}  -> True
                            _               -> False

    isNaughtyRecordSelector id = case Var.idDetails id of
                            RecSelId { sel_naughty = n } -> n
                            _                               -> False

    isClassOpId_maybe id = case Var.idDetails id of
                            ClassOpId cls -> Just cls
                            _other        -> Nothing

    isPrimOpId id = case Var.idDetails id of
                            PrimOpId _ -> True
                            _          -> False

    isDFunId id = case Var.idDetails id of
                            DFunId {} -> True
                            _         -> False

    dfunNSilent :: Id -> Int
    dfunNSilent id = case Var.idDetails id of
                       DFunId ns _ -> ns
                       _ -> pprPanic "dfunSilent: not a dfun:" (ppr id)

    isPrimOpId_maybe id = case Var.idDetails id of
                            PrimOpId op -> Just op
                            _           -> Nothing

    isFCallId id = case Var.idDetails id of
                            FCallId _ -> True
                            _         -> False

    isFCallId_maybe id = case Var.idDetails id of
                            FCallId call -> Just call
                            _            -> Nothing

    isDataConWorkId id = case Var.idDetails id of
                            DataConWorkId _ -> True
                            _               -> False

    isDataConWorkId_maybe id = case Var.idDetails id of
                            DataConWorkId con -> Just con
                            _                 -> Nothing

    isDataConId_maybe :: Id -> Maybe DataCon
    isDataConId_maybe id = case Var.idDetails id of
                             DataConWorkId con -> Just con
                             DataConWrapId con -> Just con
                             _                 -> Nothing

    idDataCon :: Id -> DataCon
    -- ^ Get from either the worker or the wrapper 'Id' to the 'DataCon'. Currently used only in the desugarer.
    --
    -- INVARIANT: @idDataCon (dataConWrapId d) = d@: remember, 'dataConWrapId' can return either the wrapper or the worker
    idDataCon id = isDataConId_maybe id `orElse` pprPanic "idDataCon" (ppr id)

    hasNoBinding :: Id -> Bool
    -- ^ Returns @True@ of an 'Id' which may not have a
    -- binding, even though it is defined in this module.

    -- Data constructor workers used to be things of this kind, but
    -- they aren't any more.  Instead, we inject a binding for
    -- them at the CorePrep stage.
    -- EXCEPT: unboxed tuples, which definitely have no binding
    hasNoBinding id = case Var.idDetails id of
                            PrimOpId _       -> True        -- See Note [Primop wrappers]
                            FCallId _        -> True
                            DataConWorkId dc -> isUnboxedTupleCon dc
                            _                -> False

    isImplicitId :: Id -> Bool
    -- ^ 'isImplicitId' tells whether an 'Id's info is implied by other
    -- declarations, so we don't need to put its signature in an interface
    -- file, even if it's mentioned in some other interface unfolding.
    isImplicitId id
      = case Var.idDetails id of
            FCallId {}       -> True
            ClassOpId {}     -> True
            PrimOpId {}      -> True
            DataConWorkId {} -> True
            DataConWrapId {} -> True
                    -- These are are implied by their type or class decl;
                    -- remember that all type and class decls appear in the interface file.
                    -- The dfun id is not an implicit Id; it must *not* be omitted, because
                    -- it carries version info for the instance decl
            _               -> False

    idIsFrom :: Module -> Id -> Bool
    idIsFrom mod id = nameIsLocalOrFrom mod (idName id)

    {-
    Note [Primop wrappers]
    ~~~~~~~~~~~~~~~~~~~~~~
    Currently hasNoBinding claims that PrimOpIds don't have a curried
    function definition.  But actually they do, in GHC.PrimopWrappers,
    which is auto-generated from prelude/primops.txt.pp.  So actually, hasNoBinding
    could return 'False' for PrimOpIds.

    But we'd need to add something in CoreToStg to swizzle any unsaturated
    applications of GHC.Prim.plusInt# to GHC.PrimopWrappers.plusInt#.

    Nota Bene: GHC.PrimopWrappers is needed *regardless*, because it's
    used by GHCi, which does not implement primops direct at all.
    -}

    isDeadBinder :: Id -> Bool
    isDeadBinder bndr | isId bndr = isDeadOcc (idOccInfo bndr)
                      | otherwise = False   -- TyVars count as not dead

    {-
    ************************************************************************
    *                                                                      *
                  Evidence variables
    *                                                                      *
    ************************************************************************
    -}

    isEvVar :: Var -> Bool
    isEvVar var = isPredTy (varType var)

    isDictId :: Id -> Bool
    isDictId id = isDictTy (idType id)

    {-
    ************************************************************************
    *                                                                      *
    \subsection{IdInfo stuff}
    *                                                                      *
    ************************************************************************
    -}

            ---------------------------------
            -- ARITY
    idArity :: Id -> Arity
    idArity id = arityInfo (idInfo id)

    setIdArity :: Id -> Arity -> Id
    setIdArity id arity = modifyIdInfo (`setArityInfo` arity) id

    idCallArity :: Id -> Arity
    idCallArity id = callArityInfo (idInfo id)

    setIdCallArity :: Id -> Arity -> Id
    setIdCallArity id arity = modifyIdInfo (`setCallArityInfo` arity) id

    idRepArity :: Id -> RepArity
    idRepArity x = typeRepArity (idArity x) (idType x)

    -- | Returns true if an application to n args would diverge
    isBottomingId :: Id -> Bool
    isBottomingId id = isBottomingSig (idStrictness id)

    idStrictness :: Id -> StrictSig
    idStrictness id = strictnessInfo (idInfo id)

    setIdStrictness :: Id -> StrictSig -> Id
    setIdStrictness id sig = modifyIdInfo (`setStrictnessInfo` sig) id

    zapIdStrictness :: Id -> Id
    zapIdStrictness id = modifyIdInfo (`setStrictnessInfo` nopSig) id

    -- | This predicate says whether the 'Id' has a strict demand placed on it or
    -- has a type such that it can always be evaluated strictly (i.e an
    -- unlifted type, as of GHC 7.6).  We need to
    -- check separately whether the 'Id' has a so-called \"strict type\" because if
    -- the demand for the given @id@ hasn't been computed yet but @id@ has a strict
    -- type, we still want @isStrictId id@ to be @True@.
    isStrictId :: Id -> Bool
    isStrictId id
      = ASSERT2( isId id, text "isStrictId: not an id: " <+> ppr id )
               (isStrictType (idType id)) ||
               -- Take the best of both strictnesses - old and new
               (isStrictDmd (idDemandInfo id))

            ---------------------------------
            -- UNFOLDING
    idUnfolding :: Id -> Unfolding
    -- Do not expose the unfolding of a loop breaker!
    idUnfolding id
      | isStrongLoopBreaker (occInfo info) = NoUnfolding
      | otherwise                          = unfoldingInfo info
      where
        info = idInfo id

    realIdUnfolding :: Id -> Unfolding
    -- Expose the unfolding if there is one, including for loop breakers
    realIdUnfolding id = unfoldingInfo (idInfo id)

    setIdUnfoldingLazily :: Id -> Unfolding -> Id
    setIdUnfoldingLazily id unfolding = modifyIdInfo (`setUnfoldingInfoLazily` unfolding) id

    setIdUnfolding :: Id -> Unfolding -> Id
    setIdUnfolding id unfolding = modifyIdInfo (`setUnfoldingInfo` unfolding) id

    idDemandInfo       :: Id -> Demand
    idDemandInfo       id = demandInfo (idInfo id)

    setIdDemandInfo :: Id -> Demand -> Id
    setIdDemandInfo id dmd = modifyIdInfo (`setDemandInfo` dmd) id

            ---------------------------------
            -- SPECIALISATION

    -- See Note [Specialisations and RULES in IdInfo] in IdInfo.lhs

    idSpecialisation :: Id -> SpecInfo
    idSpecialisation id = specInfo (idInfo id)

    idCoreRules :: Id -> [CoreRule]
    idCoreRules id = specInfoRules (idSpecialisation id)

    idHasRules :: Id -> Bool
    idHasRules id = not (isEmptySpecInfo (idSpecialisation id))

    setIdSpecialisation :: Id -> SpecInfo -> Id
    setIdSpecialisation id spec_info = modifyIdInfo (`setSpecInfo` spec_info) id

            ---------------------------------
            -- CAF INFO
    idCafInfo :: Id -> CafInfo
    idCafInfo id = cafInfo (idInfo id)

    setIdCafInfo :: Id -> CafInfo -> Id
    setIdCafInfo id caf_info = modifyIdInfo (`setCafInfo` caf_info) id

            ---------------------------------
            -- Occcurrence INFO
    idOccInfo :: Id -> OccInfo
    idOccInfo id = occInfo (idInfo id)

    setIdOccInfo :: Id -> OccInfo -> Id
    setIdOccInfo id occ_info = modifyIdInfo (`setOccInfo` occ_info) id

    zapIdOccInfo :: Id -> Id
    zapIdOccInfo b = b `setIdOccInfo` NoOccInfo

    {-
            ---------------------------------
            -- INLINING
    The inline pragma tells us to be very keen to inline this Id, but it's still
    OK not to if optimisation is switched off.
    -}

    idInlinePragma :: Id -> InlinePragma
    idInlinePragma id = inlinePragInfo (idInfo id)

    setInlinePragma :: Id -> InlinePragma -> Id
    setInlinePragma id prag = modifyIdInfo (`setInlinePragInfo` prag) id

    modifyInlinePragma :: Id -> (InlinePragma -> InlinePragma) -> Id
    modifyInlinePragma id fn = modifyIdInfo (\info -> info `setInlinePragInfo` (fn (inlinePragInfo info))) id

    idInlineActivation :: Id -> Activation
    idInlineActivation id = inlinePragmaActivation (idInlinePragma id)

    setInlineActivation :: Id -> Activation -> Id
    setInlineActivation id act = modifyInlinePragma id (\prag -> setInlinePragmaActivation prag act)

    idRuleMatchInfo :: Id -> RuleMatchInfo
    idRuleMatchInfo id = inlinePragmaRuleMatchInfo (idInlinePragma id)

    isConLikeId :: Id -> Bool
    isConLikeId id = isDataConWorkId id || isConLike (idRuleMatchInfo id)

    {-
            ---------------------------------
            -- ONE-SHOT LAMBDAS
    -}

    idOneShotInfo :: Id -> OneShotInfo
    idOneShotInfo id = oneShotInfo (idInfo id)

    -- | Returns whether the lambda associated with the 'Id' is certainly applied at most once
    -- This one is the "business end", called externally.
    -- It works on type variables as well as Ids, returning True
    -- Its main purpose is to encapsulate the Horrible State Hack
    isOneShotBndr :: Var -> Bool
    isOneShotBndr var
      | isTyVar var = True
      | otherwise   = isOneShotLambda var

    -- | Should we apply the state hack to values of this 'Type'?
    stateHackOneShot :: OneShotInfo
    stateHackOneShot = OneShotLam         -- Or maybe ProbOneShot?

    typeOneShot :: Type -> OneShotInfo
    typeOneShot ty
       | isStateHackType ty = stateHackOneShot
       | otherwise          = NoOneShotInfo

    isStateHackType :: Type -> Bool
    isStateHackType ty
      | opt_NoStateHack
      = False
      | otherwise
      = case tyConAppTyCon_maybe ty of
            Just tycon -> tycon == statePrimTyCon
            _          -> False
            -- This is a gross hack.  It claims that
            -- every function over realWorldStatePrimTy is a one-shot
            -- function.  This is pretty true in practice, and makes a big
            -- difference.  For example, consider
            --      a `thenST` \ r -> ...E...
            -- The early full laziness pass, if it doesn't know that r is one-shot
            -- will pull out E (let's say it doesn't mention r) to give
            --      let lvl = E in a `thenST` \ r -> ...lvl...
            -- When `thenST` gets inlined, we end up with
            --      let lvl = E in \s -> case a s of (r, s') -> ...lvl...
            -- and we don't re-inline E.
            --
            -- It would be better to spot that r was one-shot to start with, but
            -- I don't want to rely on that.
            --
            -- Another good example is in fill_in in PrelPack.lhs.  We should be able to
            -- spot that fill_in has arity 2 (and when Keith is done, we will) but we can't yet.

    -- | Returns whether the lambda associated with the 'Id' is certainly applied at most once.
    -- You probably want to use 'isOneShotBndr' instead
    isOneShotLambda :: Id -> Bool
    isOneShotLambda id = case idOneShotInfo id of
                           OneShotLam -> True
                           _          -> False

    isProbablyOneShotLambda :: Id -> Bool
    isProbablyOneShotLambda id = case idOneShotInfo id of
                                   OneShotLam    -> True
                                   ProbOneShot   -> True
                                   NoOneShotInfo -> False

    setOneShotLambda :: Id -> Id
    setOneShotLambda id = modifyIdInfo (`setOneShotInfo` OneShotLam) id

    clearOneShotLambda :: Id -> Id
    clearOneShotLambda id = modifyIdInfo (`setOneShotInfo` NoOneShotInfo) id

    setIdOneShotInfo :: Id -> OneShotInfo -> Id
    setIdOneShotInfo id one_shot = modifyIdInfo (`setOneShotInfo` one_shot) id

    updOneShotInfo :: Id -> OneShotInfo -> Id
    -- Combine the info in the Id with new info
    updOneShotInfo id one_shot
      | do_upd    = setIdOneShotInfo id one_shot
      | otherwise = id
      where
        do_upd = case (idOneShotInfo id, one_shot) of
                    (NoOneShotInfo, _) -> True
                    (OneShotLam,    _) -> False
                    (_, NoOneShotInfo) -> False
                    _                  -> True

    -- The OneShotLambda functions simply fiddle with the IdInfo flag
    -- But watch out: this may change the type of something else
    --      f = \x -> e
    -- If we change the one-shot-ness of x, f's type changes

    zapInfo :: (IdInfo -> Maybe IdInfo) -> Id -> Id
    zapInfo zapper id = maybeModifyIdInfo (zapper (idInfo id)) id

    zapLamIdInfo :: Id -> Id
    zapLamIdInfo = zapInfo zapLamInfo

    zapFragileIdInfo :: Id -> Id
    zapFragileIdInfo = zapInfo zapFragileInfo

    zapIdDemandInfo :: Id -> Id
    zapIdDemandInfo = zapInfo zapDemandInfo

    zapIdUsageInfo :: Id -> Id
    zapIdUsageInfo = zapInfo zapUsageInfo

    {-
    Note [transferPolyIdInfo]
    ~~~~~~~~~~~~~~~~~~~~~~~~~
    This transfer is used in two places:
            FloatOut (long-distance let-floating)
            SimplUtils.abstractFloats (short-distance let-floating)

    Consider the short-distance let-floating:

       f = /\a. let g = rhs in ...

    Then if we float thus

       g' = /\a. rhs
       f = /\a. ...[g' a/g]....

    we *do not* want to lose g's
      * strictness information
      * arity
      * inline pragma (though that is bit more debatable)
      * occurrence info

    Mostly this is just an optimisation, but it's *vital* to
    transfer the occurrence info.  Consider

       NonRec { f = /\a. let Rec { g* = ..g.. } in ... }

    where the '*' means 'LoopBreaker'.  Then if we float we must get

       Rec { g'* = /\a. ...(g' a)... }
       NonRec { f = /\a. ...[g' a/g]....}

    where g' is also marked as LoopBreaker.  If not, terrible things
    can happen if we re-simplify the binding (and the Simplifier does
    sometimes simplify a term twice); see Trac #4345.

    It's not so simple to retain
      * worker info
      * rules
    so we simply discard those.  Sooner or later this may bite us.

    If we abstract wrt one or more *value* binders, we must modify the
    arity and strictness info before transferring it.  E.g.
          f = \x. e
    -->
          g' = \y. \x. e
          + substitute (g' y) for g
    Notice that g' has an arity one more than the original g
    -}

    transferPolyIdInfo :: Id        -- Original Id
                       -> [Var]     -- Abstract wrt these variables
                       -> Id        -- New Id
                       -> Id
    transferPolyIdInfo old_id abstract_wrt new_id
      = modifyIdInfo transfer new_id
      where
        arity_increase = count isId abstract_wrt    -- Arity increases by the
                                                    -- number of value binders

        old_info        = idInfo old_id
        old_arity       = arityInfo old_info
        old_inline_prag = inlinePragInfo old_info
        old_occ_info    = occInfo old_info
        new_arity       = old_arity + arity_increase

        old_strictness  = strictnessInfo old_info
        new_strictness  = increaseStrictSigArity arity_increase old_strictness

        transfer new_info = new_info `setArityInfo` new_arity
                                     `setInlinePragInfo` old_inline_prag
                                     `setOccInfo` old_occ_info
                                     `setStrictnessInfo` new_strictness