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

\section{@Vars@: Variables}
-}

{-# LANGUAGE CPP, DeriveDataTypeable, MultiWayIf #-}

-- |
-- #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': see "Id#name_types"
--
-- * 'Var.Var' is a synonym for the 'Id.Id' type but it may additionally
--   potentially contain type variables, which have a 'TyCoRep.Kind'
--   rather than a 'TyCoRep.Type' and only contain some extra
--   details during typechecking.
--
--   These 'Var.Var' names may either be global or local, see "Var#globalvslocal"
--
-- #globalvslocal#
-- Global 'Id's and 'Var's are those that are imported or correspond
--    to a data constructor, primitive operation, or record selectors.
-- Local 'Id's and 'Var's are those bound within an expression
--    (e.g. by a lambda) or at the top level of the module being compiled.

module Var (
        -- * The main data type and synonyms
        Var, CoVar, Id, NcId, DictId, DFunId, EvVar, EqVar, EvId, IpId,
        TyVar, TypeVar, KindVar, TKVar, TyCoVar,

        -- ** Taking 'Var's apart
        varName, varUnique, varType,

        -- ** Modifying 'Var's
        setVarName, setVarUnique, setVarType, updateVarType,
        updateVarTypeM,

        -- ** Constructing, taking apart, modifying 'Id's
        mkGlobalVar, mkLocalVar, mkExportedLocalVar, mkCoVar,
        idInfo, idDetails,
        lazySetIdInfo, setIdDetails, globaliseId,
        setIdExported, setIdNotExported,

        -- ** Predicates
        isId, isTKVar, isTyVar, isTcTyVar,
        isLocalVar, isLocalId, isCoVar, isNonCoVarId, isTyCoVar,
        isGlobalId, isExportedId,
        mustHaveLocalBinding,

        -- ** Constructing 'TyVar's
        mkTyVar, mkTcTyVar,

        -- ** Taking 'TyVar's apart
        tyVarName, tyVarKind, tcTyVarDetails, setTcTyVarDetails,

        -- ** Modifying 'TyVar's
        setTyVarName, setTyVarUnique, setTyVarKind, updateTyVarKind,
        updateTyVarKindM,

        nonDetCmpVar

    ) where

#include "HsVersions.h"

import {-# SOURCE #-}   TyCoRep( Type, Kind )
import {-# SOURCE #-}   TcType( TcTyVarDetails, pprTcTyVarDetails, vanillaSkolemTv )
import {-# SOURCE #-}   IdInfo( IdDetails, IdInfo, coVarDetails, isCoVarDetails, vanillaIdInfo, pprIdDetails )

import Name hiding (varName)
import Unique
import Util
import DynFlags
import Outputable

import Unique (nonDetCmpUnique)
import Data.Data

{-
************************************************************************
*                                                                      *
                     Synonyms
*                                                                      *
************************************************************************
-- These synonyms are here and not in Id because otherwise we need a very
-- large number of SOURCE imports of Id.hs :-(
-}

type Id    = Var       -- A term-level identifier
                       --  predicate: isId

type CoVar = Id        -- See Note [Evidence: EvIds and CoVars]
                       --   predicate: isCoVar

type NcId  = Id        -- A term-level (value) variable that is
                       -- /not/ an (unlifted) coercion
                       --    predicate: isNonCoVarId

type TyVar   = Var     -- Type *or* kind variable (historical)

type TKVar   = Var     -- Type *or* kind variable (historical)
type TypeVar = Var     -- Definitely a type variable
type KindVar = Var     -- Definitely a kind variable
                       -- See Note [Kind and type variables]

-- See Note [Evidence: EvIds and CoVars]
type EvId   = Id        -- Term-level evidence: DictId, IpId, or EqVar
type EvVar  = EvId      -- ...historical name for EvId
type DFunId = Id        -- A dictionary function
type DictId = EvId      -- A dictionary variable
type IpId   = EvId      -- A term-level implicit parameter
type EqVar  = EvId      -- Boxed equality evidence

type TyCoVar = Id       -- Type, kind, *or* coercion variable
                        --   predicate: isTyCoVar

{- Note [Evidence: EvIds and CoVars]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* An EvId (evidence Id) is a term-level evidence variable
  (dictionary, implicit parameter, or equality). Could be boxed or unboxed.

* DictId, IpId, and EqVar are synonyms when we know what kind of
  evidence we are talking about.  For example, an EqVar has type (t1 ~ t2).

* A CoVar is always an un-lifted coercion, of type (t1 ~# t2) or (t1 ~R# t2)

Note [Kind and type variables]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Before kind polymorphism, TyVar were used to mean type variables. Now
they are use to mean kind *or* type variables. KindVar is used when we
know for sure that it is a kind variable. In future, we might want to
go over the whole compiler code to use:
   - TKVar   to mean kind or type variables
   - TypeVar to mean         type variables only
   - KindVar to mean kind         variables


************************************************************************
*                                                                      *
\subsection{The main data type declarations}
*                                                                      *
************************************************************************


Every @Var@ has a @Unique@, to uniquify it and for fast comparison, a
@Type@, and an @IdInfo@ (non-essential info about it, e.g.,
strictness).  The essential info about different kinds of @Vars@ is
in its @VarDetails@.
-}

-- | Essentially a typed 'Name', that may also contain some additional information
-- about the 'Var' and it's use sites.
data Var
  = TyVar {  -- Type and kind variables
             -- see Note [Kind and type variables]
        varName    :: !Name,
        realUnique :: {-# UNPACK #-} !Int,
                                     -- ^ Key for fast comparison
                                     -- Identical to the Unique in the name,
                                     -- cached here for speed
        varType    :: Kind           -- ^ The type or kind of the 'Var' in question
 }

  | TcTyVar {                           -- Used only during type inference
                                        -- Used for kind variables during
                                        -- inference, as well
        varName        :: !Name,
        realUnique     :: {-# UNPACK #-} !Int,
        varType        :: Kind,
        tc_tv_details  :: TcTyVarDetails
  }

  | Id {
        varName    :: !Name,
        realUnique :: {-# UNPACK #-} !Int,
        varType    :: Type,
        idScope    :: IdScope,
        id_details :: IdDetails,        -- Stable, doesn't change
        id_info    :: IdInfo }          -- Unstable, updated by simplifier
    deriving Typeable

data IdScope    -- See Note [GlobalId/LocalId]
  = GlobalId
  | LocalId ExportFlag

data ExportFlag   -- See Note [ExportFlag on binders]
  = NotExported   -- ^ Not exported: may be discarded as dead code.
  | Exported      -- ^ Exported: kept alive

{- Note [ExportFlag on binders]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
An ExportFlag of "Exported" on a top-level binder says "keep this
binding alive; do not drop it as dead code".  This transitively
keeps alive all the other top-level bindings that this binding refers
to.  This property is persisted all the way down the pipeline, so that
the binding will be compiled all the way to object code, and its
symbols will appear in the linker symbol table.

However, note that this use of "exported" is quite different to the
export list on a Haskell module.  Setting the ExportFlag on an Id does
/not/ mean that if you import the module (in Haskell source code) you
will see this Id.  Of course, things that appear in the export list
of the source Haskell module do indeed have their ExportFlag set.
But many other things, such as dictionary functions, are kept alive
by having their ExportFlag set, even though they are not exported
in the source-code sense.

We should probably use a different term for ExportFlag, like
KeepAlive.

Note [GlobalId/LocalId]
~~~~~~~~~~~~~~~~~~~~~~~
A GlobalId is
  * always a constant (top-level)
  * imported, or data constructor, or primop, or record selector
  * has a Unique that is globally unique across the whole
    GHC invocation (a single invocation may compile multiple modules)
  * never treated as a candidate by the free-variable finder;
        it's a constant!

A LocalId is
  * bound within an expression (lambda, case, local let(rec))
  * or defined at top level in the module being compiled
  * always treated as a candidate by the free-variable finder

After CoreTidy, top-level LocalIds are turned into GlobalIds
-}

instance Outputable Var where
  ppr var = sdocWithDynFlags $ \dflags ->
            getPprStyle $ \ppr_style ->
            if |  debugStyle ppr_style && (not (gopt Opt_SuppressVarKinds dflags))
                 -> parens (ppr (varName var) <+> ppr_debug var ppr_style <+>
                          dcolon <+> ppr (tyVarKind var))
               |  otherwise
                 -> ppr (varName var) <> ppr_debug var ppr_style

ppr_debug :: Var -> PprStyle -> SDoc
ppr_debug (TyVar {}) sty
  | debugStyle sty = brackets (text "tv")
ppr_debug (TcTyVar {tc_tv_details = d}) sty
  | dumpStyle sty || debugStyle sty = brackets (pprTcTyVarDetails d)
ppr_debug (Id { idScope = s, id_details = d }) sty
  | debugStyle sty = brackets (ppr_id_scope s <> pprIdDetails d)
ppr_debug _ _ = empty

ppr_id_scope :: IdScope -> SDoc
ppr_id_scope GlobalId              = text "gid"
ppr_id_scope (LocalId Exported)    = text "lidx"
ppr_id_scope (LocalId NotExported) = text "lid"

instance NamedThing Var where
  getName = varName

instance Uniquable Var where
  getUnique = varUnique

instance Eq Var where
    a == b = realUnique a == realUnique b

instance Ord Var where
    a <= b = realUnique a <= realUnique b
    a <  b = realUnique a <  realUnique b
    a >= b = realUnique a >= realUnique b
    a >  b = realUnique a >  realUnique b
    a `compare` b = a `nonDetCmpVar` b

-- | Compare Vars by their Uniques.
-- This is what Ord Var does, provided here to make it explicit at the
-- call-site that it can introduce non-determinism.
-- See Note [Unique Determinism]
nonDetCmpVar :: Var -> Var -> Ordering
nonDetCmpVar a b = varUnique a `nonDetCmpUnique` varUnique b

instance Data Var where
  -- don't traverse?
  toConstr _   = abstractConstr "Var"
  gunfold _ _  = error "gunfold"
  dataTypeOf _ = mkNoRepType "Var"

varUnique :: Var -> Unique
varUnique var = mkUniqueGrimily (realUnique var)

setVarUnique :: Var -> Unique -> Var
setVarUnique var uniq
  = var { realUnique = getKey uniq,
          varName = setNameUnique (varName var) uniq }

setVarName :: Var -> Name -> Var
setVarName var new_name
  = var { realUnique = getKey (getUnique new_name),
          varName = new_name }

setVarType :: Id -> Type -> Id
setVarType id ty = id { varType = ty }

updateVarType :: (Type -> Type) -> Id -> Id
updateVarType f id = id { varType = f (varType id) }

updateVarTypeM :: Monad m => (Type -> m Type) -> Id -> m Id
updateVarTypeM f id = do { ty' <- f (varType id)
                         ; return (id { varType = ty' }) }

{-
************************************************************************
*                                                                      *
\subsection{Type and kind variables}
*                                                                      *
************************************************************************
-}

tyVarName :: TyVar -> Name
tyVarName = varName

tyVarKind :: TyVar -> Kind
tyVarKind = varType

setTyVarUnique :: TyVar -> Unique -> TyVar
setTyVarUnique = setVarUnique

setTyVarName :: TyVar -> Name -> TyVar
setTyVarName   = setVarName

setTyVarKind :: TyVar -> Kind -> TyVar
setTyVarKind tv k = tv {varType = k}

updateTyVarKind :: (Kind -> Kind) -> TyVar -> TyVar
updateTyVarKind update tv = tv {varType = update (tyVarKind tv)}

updateTyVarKindM :: (Monad m) => (Kind -> m Kind) -> TyVar -> m TyVar
updateTyVarKindM update tv
  = do { k' <- update (tyVarKind tv)
       ; return $ tv {varType = k'} }

mkTyVar :: Name -> Kind -> TyVar
mkTyVar name kind = TyVar { varName    = name
                          , realUnique = getKey (nameUnique name)
                          , varType  = kind
                          }

mkTcTyVar :: Name -> Kind -> TcTyVarDetails -> TyVar
mkTcTyVar name kind details
  = -- NB: 'kind' may be a coercion kind; cf, 'TcMType.newMetaCoVar'
    TcTyVar {   varName    = name,
                realUnique = getKey (nameUnique name),
                varType  = kind,
                tc_tv_details = details
        }

tcTyVarDetails :: TyVar -> TcTyVarDetails
tcTyVarDetails (TcTyVar { tc_tv_details = details }) = details
tcTyVarDetails (TyVar {})                            = vanillaSkolemTv
tcTyVarDetails var = pprPanic "tcTyVarDetails" (ppr var <+> dcolon <+> ppr (tyVarKind var))

setTcTyVarDetails :: TyVar -> TcTyVarDetails -> TyVar
setTcTyVarDetails tv details = tv { tc_tv_details = details }

{-
%************************************************************************
%*                                                                      *
\subsection{Ids}
*                                                                      *
************************************************************************
-}

idInfo :: Id -> IdInfo
idInfo (Id { id_info = info }) = info
idInfo other                   = pprPanic "idInfo" (ppr other)

idDetails :: Id -> IdDetails
idDetails (Id { id_details = details }) = details
idDetails other                         = pprPanic "idDetails" (ppr other)

-- The next three have a 'Var' suffix even though they always build
-- Ids, because Id.hs uses 'mkGlobalId' etc with different types
mkGlobalVar :: IdDetails -> Name -> Type -> IdInfo -> Id
mkGlobalVar details name ty info
  = mk_id name ty GlobalId details info

mkLocalVar :: IdDetails -> Name -> Type -> IdInfo -> Id
mkLocalVar details name ty info
  = mk_id name ty (LocalId NotExported) details  info

mkCoVar :: Name -> Type -> CoVar
-- Coercion variables have no IdInfo
mkCoVar name ty = mk_id name ty (LocalId NotExported) coVarDetails vanillaIdInfo

-- | Exported 'Var's will not be removed as dead code
mkExportedLocalVar :: IdDetails -> Name -> Type -> IdInfo -> Id
mkExportedLocalVar details name ty info
  = mk_id name ty (LocalId Exported) details info

mk_id :: Name -> Type -> IdScope -> IdDetails -> IdInfo -> Id
mk_id name ty scope details info
  = Id { varName    = name,
         realUnique = getKey (nameUnique name),
         varType    = ty,
         idScope    = scope,
         id_details = details,
         id_info    = info }

-------------------
lazySetIdInfo :: Id -> IdInfo -> Var
lazySetIdInfo id info = id { id_info = info }

setIdDetails :: Id -> IdDetails -> Id
setIdDetails id details = id { id_details = details }

globaliseId :: Id -> Id
-- ^ If it's a local, make it global
globaliseId id = id { idScope = GlobalId }

setIdExported :: Id -> Id
-- ^ Exports the given local 'Id'. Can also be called on global 'Id's, such as data constructors
-- and class operations, which are born as global 'Id's and automatically exported
setIdExported id@(Id { idScope = LocalId {} }) = id { idScope = LocalId Exported }
setIdExported id@(Id { idScope = GlobalId })   = id
setIdExported tv                               = pprPanic "setIdExported" (ppr tv)

setIdNotExported :: Id -> Id
-- ^ We can only do this to LocalIds
setIdNotExported id = ASSERT( isLocalId id )
                      id { idScope = LocalId NotExported }

{-
************************************************************************
*                                                                      *
\subsection{Predicates over variables}
*                                                                      *
************************************************************************
-}

isTyVar :: Var -> Bool
isTyVar = isTKVar     -- Historical

isTKVar :: Var -> Bool  -- True of both type and kind variables
isTKVar (TyVar {})   = True
isTKVar (TcTyVar {}) = True
isTKVar _            = False

isTcTyVar :: Var -> Bool
isTcTyVar (TcTyVar {}) = True
isTcTyVar _            = False

isTyCoVar :: Var -> Bool
isTyCoVar v = isTyVar v || isCoVar v

isId :: Var -> Bool
isId (Id {}) = True
isId _       = False

isCoVar :: Var -> Bool
-- A coercion variable
isCoVar (Id { id_details = details }) = isCoVarDetails details
isCoVar _                             = False

isNonCoVarId :: Var -> Bool
-- A term variable (Id) that is /not/ a coercion variable
isNonCoVarId (Id { id_details = details }) = not (isCoVarDetails details)
isNonCoVarId _                             = False

isLocalId :: Var -> Bool
isLocalId (Id { idScope = LocalId _ }) = True
isLocalId _                            = False

-- | 'isLocalVar' returns @True@ for type variables as well as local 'Id's
-- These are the variables that we need to pay attention to when finding free
-- variables, or doing dependency analysis.
isLocalVar :: Var -> Bool
isLocalVar v = not (isGlobalId v)

isGlobalId :: Var -> Bool
isGlobalId (Id { idScope = GlobalId }) = True
isGlobalId _                           = False

-- | 'mustHaveLocalBinding' returns @True@ of 'Id's and 'TyVar's
-- that must have a binding in this module.  The converse
-- is not quite right: there are some global 'Id's that must have
-- bindings, such as record selectors.  But that doesn't matter,
-- because it's only used for assertions
mustHaveLocalBinding        :: Var -> Bool
mustHaveLocalBinding var = isLocalVar var

-- | 'isExportedIdVar' means \"don't throw this away\"
isExportedId :: Var -> Bool
isExportedId (Id { idScope = GlobalId })        = True
isExportedId (Id { idScope = LocalId Exported}) = True
isExportedId _ = False
