%
% (c) The University of Glasgow 2006
% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
\section[Id]{@Ids@: Value and constructor identifiers}

\begin{code}
-- |
-- #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,
        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, zapDemandIdInfo, zapFragileIdInfo, transferPolyIdInfo,
        zapIdStrictness,

        -- ** 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, 
        idUnfolding, realIdUnfolding,
        idSpecialisation, idCoreRules, idHasRules,
        idCafInfo,
        idOneShotInfo,
        idOccInfo,

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

        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`,
          `setIdOccInfo`,
          `setIdOneShotInfo`,

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

          `setIdDemandInfo`,
          `setIdStrictness`
\end{code}

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

\begin{code}
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
\end{code}

%************************************************************************
%*                                                                      *
\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.

\begin{code}
-- | 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.
mkExportedLocalId :: Name -> Type -> Id
mkExportedLocalId name ty = Var.mkExportedLocalVar VanillaId 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))

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

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.

\begin{code}
-- | 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
\end{code}


%************************************************************************
%*                                                                      *
\subsection{Special Ids}
%*                                                                      *
%************************************************************************

\begin{code}
-- | 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)
\end{code}

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.



\begin{code}
isDeadBinder :: Id -> Bool
isDeadBinder bndr | isId bndr = isDeadOcc (idOccInfo bndr)
                  | otherwise = False   -- TyVars count as not dead
\end{code}

%************************************************************************
%*                                                                      *
              Evidence variables
%*                                                                      *
%************************************************************************

\begin{code}
isEvVar :: Var -> Bool
isEvVar var = isPredTy (varType var)

isDictId :: Id -> Bool
isDictId id = isDictTy (idType id)
\end{code}

%************************************************************************
%*                                                                      *
\subsection{IdInfo stuff}
%*                                                                      *
%************************************************************************

\begin{code}
        ---------------------------------
        -- ARITY
idArity :: Id -> Arity
idArity id = arityInfo (idInfo id)

setIdArity :: Id -> Arity -> Id
setIdArity id arity = modifyIdInfo (`setArityInfo` 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
\end{code}


        ---------------------------------
        -- 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.

\begin{code}
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)
\end{code}


        ---------------------------------
        -- ONE-SHOT LAMBDAS
\begin{code}
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
\end{code}

\begin{code}
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 

zapDemandIdInfo :: Id -> Id
zapDemandIdInfo = zapInfo zapDemandInfo
\end{code}

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

\begin{code}
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
\end{code}
