basicTypes/BasicTypes.hs

    {-
    (c) The University of Glasgow 2006
    (c) The GRASP/AQUA Project, Glasgow University, 1997-1998

    \section[BasicTypes]{Miscellanous types}

    This module defines a miscellaneously collection of very simple
    types that

    \begin{itemize}
    \item have no other obvious home
    \item don't depend on any other complicated types
    \item are used in more than one "part" of the compiler
    \end{itemize}
    -}

    {-# LANGUAGE DeriveDataTypeable #-}

    module BasicTypes(
            Version, bumpVersion, initialVersion,

            ConTag, fIRST_TAG,

            Arity, RepArity,

            Alignment,

            FunctionOrData(..),

            WarningTxt(..), StringLiteral(..),

            Fixity(..), FixityDirection(..),
            defaultFixity, maxPrecedence, minPrecedence,
            negateFixity, funTyFixity,
            compareFixity,

            RecFlag(..), isRec, isNonRec, boolToRecFlag,
            Origin(..), isGenerated,

            RuleName, pprRuleName,

            TopLevelFlag(..), isTopLevel, isNotTopLevel,

            OverlapFlag(..), OverlapMode(..), setOverlapModeMaybe,
            hasOverlappingFlag, hasOverlappableFlag,

            Boxity(..), isBoxed,

            TupleSort(..), tupleSortBoxity, boxityTupleSort,
            tupleParens,

            -- ** The OneShotInfo type
            OneShotInfo(..),
            noOneShotInfo, hasNoOneShotInfo, isOneShotInfo,
            bestOneShot, worstOneShot,

            OccInfo(..), seqOccInfo, zapFragileOcc, isOneOcc,
            isDeadOcc, isStrongLoopBreaker, isWeakLoopBreaker, isNoOcc,
            strongLoopBreaker, weakLoopBreaker,

            InsideLam, insideLam, notInsideLam,
            OneBranch, oneBranch, notOneBranch,
            InterestingCxt,

            EP(..),

            DefMethSpec(..),
            SwapFlag(..), flipSwap, unSwap, isSwapped,

            CompilerPhase(..), PhaseNum,

            Activation(..), isActive, isActiveIn, competesWith,
            isNeverActive, isAlwaysActive, isEarlyActive,

            RuleMatchInfo(..), isConLike, isFunLike,
            InlineSpec(..), isEmptyInlineSpec,
            InlinePragma(..), defaultInlinePragma, alwaysInlinePragma,
            neverInlinePragma, dfunInlinePragma,
            isDefaultInlinePragma,
            isInlinePragma, isInlinablePragma, isAnyInlinePragma,
            inlinePragmaSpec, inlinePragmaSat,
            inlinePragmaActivation, inlinePragmaRuleMatchInfo,
            setInlinePragmaActivation, setInlinePragmaRuleMatchInfo,

            SuccessFlag(..), succeeded, failed, successIf,

            FractionalLit(..), negateFractionalLit, integralFractionalLit,

            SourceText,

            IntWithInf, infinity, treatZeroAsInf, mkIntWithInf, intGtLimit
       ) where

    import FastString
    import Outputable
    import SrcLoc ( Located,unLoc )
    import StaticFlags( opt_PprStyle_Debug )
    import Data.Data hiding (Fixity)
    import Data.Function (on)

    {-
    ************************************************************************
    *                                                                      *
    \subsection[Arity]{Arity}
    *                                                                      *
    ************************************************************************
    -}

    -- | The number of value arguments that can be applied to a value before it does
    -- "real work". So:
    --  fib 100     has arity 0
    --  \x -> fib x has arity 1
    type Arity = Int

    -- | The number of represented arguments that can be applied to a value before it does
    -- "real work". So:
    --  fib 100                    has representation arity 0
    --  \x -> fib x                has representation arity 1
    --  \(# x, y #) -> fib (x + y) has representation arity 2
    type RepArity = Int

    {-
    ************************************************************************
    *                                                                      *
                  Constructor tags
    *                                                                      *
    ************************************************************************
    -}

    -- | Type of the tags associated with each constructor possibility
    --   or superclass selector
    type ConTag = Int

    fIRST_TAG :: ConTag
    -- ^ Tags are allocated from here for real constructors
    --   or for superclass selectors
    fIRST_TAG =  1

    {-
    ************************************************************************
    *                                                                      *
    \subsection[Alignment]{Alignment}
    *                                                                      *
    ************************************************************************
    -}

    type Alignment = Int -- align to next N-byte boundary (N must be a power of 2).

    {-
    ************************************************************************
    *                                                                      *
             One-shot information
    *                                                                      *
    ************************************************************************
    -}

    -- | If the 'Id' is a lambda-bound variable then it may have lambda-bound
    -- variable info. Sometimes we know whether the lambda binding this variable
    -- is a \"one-shot\" lambda; that is, whether it is applied at most once.
    --
    -- This information may be useful in optimisation, as computations may
    -- safely be floated inside such a lambda without risk of duplicating
    -- work.
    data OneShotInfo
      = NoOneShotInfo -- ^ No information
      | ProbOneShot   -- ^ The lambda is probably applied at most once
                      -- See Note [Computing one-shot info, and ProbOneShot] in Demand
      | OneShotLam    -- ^ The lambda is applied at most once.
      deriving (Eq)

    -- | It is always safe to assume that an 'Id' has no lambda-bound variable information
    noOneShotInfo :: OneShotInfo
    noOneShotInfo = NoOneShotInfo

    isOneShotInfo, hasNoOneShotInfo :: OneShotInfo -> Bool
    isOneShotInfo OneShotLam = True
    isOneShotInfo _          = False

    hasNoOneShotInfo NoOneShotInfo = True
    hasNoOneShotInfo _             = False

    worstOneShot, bestOneShot :: OneShotInfo -> OneShotInfo -> OneShotInfo
    worstOneShot NoOneShotInfo _             = NoOneShotInfo
    worstOneShot ProbOneShot   NoOneShotInfo = NoOneShotInfo
    worstOneShot ProbOneShot   _             = ProbOneShot
    worstOneShot OneShotLam    os            = os

    bestOneShot NoOneShotInfo os         = os
    bestOneShot ProbOneShot   OneShotLam = OneShotLam
    bestOneShot ProbOneShot   _          = ProbOneShot
    bestOneShot OneShotLam    _          = OneShotLam

    pprOneShotInfo :: OneShotInfo -> SDoc
    pprOneShotInfo NoOneShotInfo = empty
    pprOneShotInfo ProbOneShot   = text "ProbOneShot"
    pprOneShotInfo OneShotLam    = text "OneShot"

    instance Outputable OneShotInfo where
        ppr = pprOneShotInfo

    {-
    ************************************************************************
    *                                                                      *
               Swap flag
    *                                                                      *
    ************************************************************************
    -}

    data SwapFlag
      = NotSwapped  -- Args are: actual,   expected
      | IsSwapped   -- Args are: expected, actual

    instance Outputable SwapFlag where
      ppr IsSwapped  = text "Is-swapped"
      ppr NotSwapped = text "Not-swapped"

    flipSwap :: SwapFlag -> SwapFlag
    flipSwap IsSwapped  = NotSwapped
    flipSwap NotSwapped = IsSwapped

    isSwapped :: SwapFlag -> Bool
    isSwapped IsSwapped  = True
    isSwapped NotSwapped = False

    unSwap :: SwapFlag -> (a->a->b) -> a -> a -> b
    unSwap NotSwapped f a b = f a b
    unSwap IsSwapped  f a b = f b a

    {-
    ************************************************************************
    *                                                                      *
    \subsection[FunctionOrData]{FunctionOrData}
    *                                                                      *
    ************************************************************************
    -}

    data FunctionOrData = IsFunction | IsData
        deriving (Eq, Ord, Data, Typeable)

    instance Outputable FunctionOrData where
        ppr IsFunction = text "(function)"
        ppr IsData     = text "(data)"

    {-
    ************************************************************************
    *                                                                      *
    \subsection[Version]{Module and identifier version numbers}
    *                                                                      *
    ************************************************************************
    -}

    type Version = Int

    bumpVersion :: Version -> Version
    bumpVersion v = v+1

    initialVersion :: Version
    initialVersion = 1

    {-
    ************************************************************************
    *                                                                      *
                    Deprecations
    *                                                                      *
    ************************************************************************
    -}

    -- |A String Literal in the source, including its original raw format for use by
    -- source to source manipulation tools.
    data StringLiteral = StringLiteral
                           { sl_st :: SourceText, -- literal raw source.
                                                  -- See not [Literal source text]
                             sl_fs :: FastString  -- literal string value
                           } deriving (Data, Typeable)

    instance Eq StringLiteral where
      (StringLiteral _ a) == (StringLiteral _ b) = a == b

    -- reason/explanation from a WARNING or DEPRECATED pragma
    data WarningTxt = WarningTxt (Located SourceText)
                                 [Located StringLiteral]
                    | DeprecatedTxt (Located SourceText)
                                    [Located StringLiteral]
        deriving (Eq, Data, Typeable)

    instance Outputable WarningTxt where
        ppr (WarningTxt    _ ws)
                             = doubleQuotes (vcat (map (ftext . sl_fs . unLoc) ws))
        ppr (DeprecatedTxt _ ds)
                             = text "Deprecated:" <+>
                               doubleQuotes (vcat (map (ftext . sl_fs . unLoc) ds))

    {-
    ************************************************************************
    *                                                                      *
                    Rules
    *                                                                      *
    ************************************************************************
    -}

    type RuleName = FastString

    pprRuleName :: RuleName -> SDoc
    pprRuleName rn = doubleQuotes (ftext rn)

    {-
    ************************************************************************
    *                                                                      *
    \subsection[Fixity]{Fixity info}
    *                                                                      *
    ************************************************************************
    -}

    ------------------------
    data Fixity = Fixity SourceText Int FixityDirection
      -- Note [Pragma source text]
      deriving (Data, Typeable)

    instance Outputable Fixity where
        ppr (Fixity _ prec dir) = hcat [ppr dir, space, int prec]

    instance Eq Fixity where -- Used to determine if two fixities conflict
      (Fixity _ p1 dir1) == (Fixity _ p2 dir2) = p1==p2 && dir1 == dir2

    ------------------------
    data FixityDirection = InfixL | InfixR | InfixN
                         deriving (Eq, Data, Typeable)

    instance Outputable FixityDirection where
        ppr InfixL = text "infixl"
        ppr InfixR = text "infixr"
        ppr InfixN = text "infix"

    ------------------------
    maxPrecedence, minPrecedence :: Int
    maxPrecedence = 9
    minPrecedence = 0

    defaultFixity :: Fixity
    defaultFixity = Fixity (show maxPrecedence) maxPrecedence InfixL

    negateFixity, funTyFixity :: Fixity
    -- Wired-in fixities
    negateFixity = Fixity "6" 6 InfixL  -- Fixity of unary negate
    funTyFixity  = Fixity "0" 0 InfixR  -- Fixity of '->'

    {-
    Consider

    \begin{verbatim}
            a `op1` b `op2` c
    \end{verbatim}
    @(compareFixity op1 op2)@ tells which way to arrange appication, or
    whether there's an error.
    -}

    compareFixity :: Fixity -> Fixity
                  -> (Bool,         -- Error please
                      Bool)         -- Associate to the right: a op1 (b op2 c)
    compareFixity (Fixity _ prec1 dir1) (Fixity _ prec2 dir2)
      = case prec1 `compare` prec2 of
            GT -> left
            LT -> right
            EQ -> case (dir1, dir2) of
                            (InfixR, InfixR) -> right
                            (InfixL, InfixL) -> left
                            _                -> error_please
      where
        right        = (False, True)
        left         = (False, False)
        error_please = (True,  False)

    {-
    ************************************************************************
    *                                                                      *
    \subsection[Top-level/local]{Top-level/not-top level flag}
    *                                                                      *
    ************************************************************************
    -}

    data TopLevelFlag
      = TopLevel
      | NotTopLevel

    isTopLevel, isNotTopLevel :: TopLevelFlag -> Bool

    isNotTopLevel NotTopLevel = True
    isNotTopLevel TopLevel    = False

    isTopLevel TopLevel     = True
    isTopLevel NotTopLevel  = False

    instance Outputable TopLevelFlag where
      ppr TopLevel    = text "<TopLevel>"
      ppr NotTopLevel = text "<NotTopLevel>"

    {-
    ************************************************************************
    *                                                                      *
                    Boxity flag
    *                                                                      *
    ************************************************************************
    -}

    data Boxity
      = Boxed
      | Unboxed
      deriving( Eq, Data, Typeable )

    isBoxed :: Boxity -> Bool
    isBoxed Boxed   = True
    isBoxed Unboxed = False

    instance Outputable Boxity where
      ppr Boxed   = text "Boxed"
      ppr Unboxed = text "Unboxed"

    {-
    ************************************************************************
    *                                                                      *
                    Recursive/Non-Recursive flag
    *                                                                      *
    ************************************************************************
    -}

    data RecFlag = Recursive
                 | NonRecursive
                 deriving( Eq, Data, Typeable )

    isRec :: RecFlag -> Bool
    isRec Recursive    = True
    isRec NonRecursive = False

    isNonRec :: RecFlag -> Bool
    isNonRec Recursive    = False
    isNonRec NonRecursive = True

    boolToRecFlag :: Bool -> RecFlag
    boolToRecFlag True  = Recursive
    boolToRecFlag False = NonRecursive

    instance Outputable RecFlag where
      ppr Recursive    = text "Recursive"
      ppr NonRecursive = text "NonRecursive"

    {-
    ************************************************************************
    *                                                                      *
                    Code origin
    *                                                                      *
    ************************************************************************
    -}

    data Origin = FromSource
                | Generated
                deriving( Eq, Data, Typeable )

    isGenerated :: Origin -> Bool
    isGenerated Generated = True
    isGenerated FromSource = False

    instance Outputable Origin where
      ppr FromSource  = text "FromSource"
      ppr Generated   = text "Generated"

    {-
    ************************************************************************
    *                                                                      *
                    Instance overlap flag
    *                                                                      *
    ************************************************************************
    -}

    -- | The semantics allowed for overlapping instances for a particular
    -- instance. See Note [Safe Haskell isSafeOverlap] (in `InstEnv.hs`) for a
    -- explanation of the `isSafeOverlap` field.
    --
    -- - 'ApiAnnotation.AnnKeywordId' :
    --      'ApiAnnotation.AnnOpen' @'\{-\# OVERLAPPABLE'@ or
    --                              @'\{-\# OVERLAPPING'@ or
    --                              @'\{-\# OVERLAPS'@ or
    --                              @'\{-\# INCOHERENT'@,
    --      'ApiAnnotation.AnnClose' @`\#-\}`@,

    -- For details on above see note [Api annotations] in ApiAnnotation
    data OverlapFlag = OverlapFlag
      { overlapMode   :: OverlapMode
      , isSafeOverlap :: Bool
      } deriving (Eq, Data, Typeable)

    setOverlapModeMaybe :: OverlapFlag -> Maybe OverlapMode -> OverlapFlag
    setOverlapModeMaybe f Nothing  = f
    setOverlapModeMaybe f (Just m) = f { overlapMode = m }

    hasOverlappableFlag :: OverlapMode -> Bool
    hasOverlappableFlag mode =
      case mode of
        Overlappable _ -> True
        Overlaps     _ -> True
        Incoherent   _ -> True
        _              -> False

    hasOverlappingFlag :: OverlapMode -> Bool
    hasOverlappingFlag mode =
      case mode of
        Overlapping  _ -> True
        Overlaps     _ -> True
        Incoherent   _ -> True
        _              -> False

    data OverlapMode  -- See Note [Rules for instance lookup] in InstEnv
      = NoOverlap SourceText
                      -- See Note [Pragma source text]
        -- ^ This instance must not overlap another `NoOverlap` instance.
        -- However, it may be overlapped by `Overlapping` instances,
        -- and it may overlap `Overlappable` instances.

      | Overlappable SourceText
                      -- See Note [Pragma source text]
        -- ^ Silently ignore this instance if you find a
        -- more specific one that matches the constraint
        -- you are trying to resolve
        --
        -- Example: constraint (Foo [Int])
        --   instance                      Foo [Int]
        --   instance {-# OVERLAPPABLE #-} Foo [a]
        --
        -- Since the second instance has the Overlappable flag,
        -- the first instance will be chosen (otherwise
        -- its ambiguous which to choose)

      | Overlapping SourceText
                      -- See Note [Pragma source text]
        -- ^ Silently ignore any more general instances that may be
        --   used to solve the constraint.
        --
        -- Example: constraint (Foo [Int])
        --   instance {-# OVERLAPPING #-} Foo [Int]
        --   instance                     Foo [a]
        --
        -- Since the first instance has the Overlapping flag,
        -- the second---more general---instance will be ignored (otherwise
        -- it is ambiguous which to choose)

      | Overlaps SourceText
                      -- See Note [Pragma source text]
        -- ^ Equivalent to having both `Overlapping` and `Overlappable` flags.

      | Incoherent SourceText
                      -- See Note [Pragma source text]
        -- ^ Behave like Overlappable and Overlapping, and in addition pick
        -- an an arbitrary one if there are multiple matching candidates, and
        -- don't worry about later instantiation
        --
        -- Example: constraint (Foo [b])
        -- instance {-# INCOHERENT -} Foo [Int]
        -- instance                   Foo [a]
        -- Without the Incoherent flag, we'd complain that
        -- instantiating 'b' would change which instance
        -- was chosen. See also note [Incoherent instances] in InstEnv

      deriving (Eq, Data, Typeable)

    instance Outputable OverlapFlag where
       ppr flag = ppr (overlapMode flag) <+> pprSafeOverlap (isSafeOverlap flag)

    instance Outputable OverlapMode where
       ppr (NoOverlap    _) = empty
       ppr (Overlappable _) = text "[overlappable]"
       ppr (Overlapping  _) = text "[overlapping]"
       ppr (Overlaps     _) = text "[overlap ok]"
       ppr (Incoherent   _) = text "[incoherent]"

    pprSafeOverlap :: Bool -> SDoc
    pprSafeOverlap True  = text "[safe]"
    pprSafeOverlap False = empty

    {-
    ************************************************************************
    *                                                                      *
                    Tuples
    *                                                                      *
    ************************************************************************
    -}

    data TupleSort
      = BoxedTuple
      | UnboxedTuple
      | ConstraintTuple
      deriving( Eq, Data, Typeable )

    tupleSortBoxity :: TupleSort -> Boxity
    tupleSortBoxity BoxedTuple      = Boxed
    tupleSortBoxity UnboxedTuple    = Unboxed
    tupleSortBoxity ConstraintTuple = Boxed

    boxityTupleSort :: Boxity -> TupleSort
    boxityTupleSort Boxed   = BoxedTuple
    boxityTupleSort Unboxed = UnboxedTuple

    tupleParens :: TupleSort -> SDoc -> SDoc
    tupleParens BoxedTuple      p = parens p
    tupleParens UnboxedTuple    p = text "(#" <+> p <+> ptext (sLit "#)")
    tupleParens ConstraintTuple p   -- In debug-style write (% Eq a, Ord b %)
      | opt_PprStyle_Debug        = text "(%" <+> p <+> ptext (sLit "%)")
      | otherwise                 = parens p

    {-
    ************************************************************************
    *                                                                      *
    \subsection[Generic]{Generic flag}
    *                                                                      *
    ************************************************************************

    This is the "Embedding-Projection pair" datatype, it contains
    two pieces of code (normally either RenamedExpr's or Id's)
    If we have a such a pair (EP from to), the idea is that 'from' and 'to'
    represents functions of type

            from :: T -> Tring
            to   :: Tring -> T

    And we should have

            to (from x) = x

    T and Tring are arbitrary, but typically T is the 'main' type while
    Tring is the 'representation' type.  (This just helps us remember
    whether to use 'from' or 'to'.
    -}

    data EP a = EP { fromEP :: a,   -- :: T -> Tring
                     toEP   :: a }  -- :: Tring -> T

    {-
    Embedding-projection pairs are used in several places:

    First of all, each type constructor has an EP associated with it, the
    code in EP converts (datatype T) from T to Tring and back again.

    Secondly, when we are filling in Generic methods (in the typechecker,
    tcMethodBinds), we are constructing bimaps by induction on the structure
    of the type of the method signature.

    ************************************************************************
    *                                                                      *
    \subsection{Occurrence information}
    *                                                                      *
    ************************************************************************

    This data type is used exclusively by the simplifier, but it appears in a
    SubstResult, which is currently defined in VarEnv, which is pretty near
    the base of the module hierarchy.  So it seemed simpler to put the
    defn of OccInfo here, safely at the bottom
    -}

    -- | Identifier occurrence information
    data OccInfo
      = NoOccInfo           -- ^ There are many occurrences, or unknown occurrences

      | IAmDead             -- ^ Marks unused variables.  Sometimes useful for
                            -- lambda and case-bound variables.

      | OneOcc
            !InsideLam
            !OneBranch
            !InterestingCxt -- ^ Occurs exactly once, not inside a rule

      -- | This identifier breaks a loop of mutually recursive functions. The field
      -- marks whether it is only a loop breaker due to a reference in a rule
      | IAmALoopBreaker     -- Note [LoopBreaker OccInfo]
            !RulesOnly

      deriving (Eq)

    type RulesOnly = Bool

    {-
    Note [LoopBreaker OccInfo]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~
       IAmALoopBreaker True  <=> A "weak" or rules-only loop breaker
                                 Do not preInlineUnconditionally

       IAmALoopBreaker False <=> A "strong" loop breaker
                                 Do not inline at all

    See OccurAnal Note [Weak loop breakers]
    -}

    isNoOcc :: OccInfo -> Bool
    isNoOcc NoOccInfo = True
    isNoOcc _         = False

    seqOccInfo :: OccInfo -> ()
    seqOccInfo occ = occ `seq` ()

    -----------------
    type InterestingCxt = Bool      -- True <=> Function: is applied
                                    --          Data value: scrutinised by a case with
                                    --                      at least one non-DEFAULT branch

    -----------------
    type InsideLam = Bool   -- True <=> Occurs inside a non-linear lambda
                            -- Substituting a redex for this occurrence is
                            -- dangerous because it might duplicate work.
    insideLam, notInsideLam :: InsideLam
    insideLam    = True
    notInsideLam = False

    -----------------
    type OneBranch = Bool   -- True <=> Occurs in only one case branch
                            --      so no code-duplication issue to worry about
    oneBranch, notOneBranch :: OneBranch
    oneBranch    = True
    notOneBranch = False

    strongLoopBreaker, weakLoopBreaker :: OccInfo
    strongLoopBreaker = IAmALoopBreaker False
    weakLoopBreaker   = IAmALoopBreaker True

    isWeakLoopBreaker :: OccInfo -> Bool
    isWeakLoopBreaker (IAmALoopBreaker _) = True
    isWeakLoopBreaker _                   = False

    isStrongLoopBreaker :: OccInfo -> Bool
    isStrongLoopBreaker (IAmALoopBreaker False) = True   -- Loop-breaker that breaks a non-rule cycle
    isStrongLoopBreaker _                       = False

    isDeadOcc :: OccInfo -> Bool
    isDeadOcc IAmDead = True
    isDeadOcc _       = False

    isOneOcc :: OccInfo -> Bool
    isOneOcc (OneOcc {}) = True
    isOneOcc _           = False

    zapFragileOcc :: OccInfo -> OccInfo
    zapFragileOcc (OneOcc {}) = NoOccInfo
    zapFragileOcc occ         = occ

    instance Outputable OccInfo where
      -- only used for debugging; never parsed.  KSW 1999-07
      ppr NoOccInfo            = empty
      ppr (IAmALoopBreaker ro) = text "LoopBreaker" <> if ro then char '!' else empty
      ppr IAmDead              = text "Dead"
      ppr (OneOcc inside_lam one_branch int_cxt)
            = text "Once" <> pp_lam <> pp_br <> pp_args
            where
              pp_lam | inside_lam = char 'L'
                     | otherwise  = empty
              pp_br  | one_branch = empty
                     | otherwise  = char '*'
              pp_args | int_cxt   = char '!'
                      | otherwise = empty

    {-
    ************************************************************************
    *                                                                      *
                    Default method specfication
    *                                                                      *
    ************************************************************************

    The DefMethSpec enumeration just indicates what sort of default method
    is used for a class. It is generated from source code, and present in
    interface files; it is converted to Class.DefMethInfo before begin put in a
    Class object.
    -}

    data DefMethSpec ty
      = VanillaDM     -- Default method given with polymorphic code
      | GenericDM ty  -- Default method given with code of this type

    instance Outputable (DefMethSpec ty) where
      ppr VanillaDM      = text "{- Has default method -}"
      ppr (GenericDM {}) = text "{- Has generic default method -}"

    {-
    ************************************************************************
    *                                                                      *
    \subsection{Success flag}
    *                                                                      *
    ************************************************************************
    -}

    data SuccessFlag = Succeeded | Failed

    instance Outputable SuccessFlag where
        ppr Succeeded = text "Succeeded"
        ppr Failed    = text "Failed"

    successIf :: Bool -> SuccessFlag
    successIf True  = Succeeded
    successIf False = Failed

    succeeded, failed :: SuccessFlag -> Bool
    succeeded Succeeded = True
    succeeded Failed    = False

    failed Succeeded = False
    failed Failed    = True

    {-
    ************************************************************************
    *                                                                      *
    \subsection{Source Text}
    *                                                                      *
    ************************************************************************
    Keeping Source Text for source to source conversions

    Note [Pragma source text]
    ~~~~~~~~~~~~~~~~~~~~~~~~~
    The lexer does a case-insensitive match for pragmas, as well as
    accepting both UK and US spelling variants.

    So

      {-# SPECIALISE #-}
      {-# SPECIALIZE #-}
      {-# Specialize #-}

    will all generate ITspec_prag token for the start of the pragma.

    In order to be able to do source to source conversions, the original
    source text for the token needs to be preserved, hence the
    `SourceText` field.

    So the lexer will then generate

      ITspec_prag "{ -# SPECIALISE"
      ITspec_prag "{ -# SPECIALIZE"
      ITspec_prag "{ -# Specialize"

    for the cases above.
     [without the space between '{' and '-', otherwise this comment won't parse]

    Note [Literal source text]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~
    The lexer/parser converts literals from their original source text
    versions to an appropriate internal representation. This is a problem
    for tools doing source to source conversions, so the original source
    text is stored in literals where this can occur.

    Motivating examples for HsLit

      HsChar          '\n'       == '\x20`
      HsCharPrim      '\x41`#    == `A`
      HsString        "\x20\x41" == " A"
      HsStringPrim    "\x20"#    == " "#
      HsInt           001        == 1
      HsIntPrim       002#       == 2#
      HsWordPrim      003##      == 3##
      HsInt64Prim     004##      == 4##
      HsWord64Prim    005##      == 5##
      HsInteger       006        == 6

    For OverLitVal

      HsIntegral      003      == 0x003
      HsIsString      "\x41nd" == "And"
    -}

    type SourceText = String -- Note [Literal source text],[Pragma source text]

    {-
    ************************************************************************
    *                                                                      *
    \subsection{Activation}
    *                                                                      *
    ************************************************************************

    When a rule or inlining is active
    -}

    type PhaseNum = Int  -- Compilation phase
                         -- Phases decrease towards zero
                         -- Zero is the last phase

    data CompilerPhase
      = Phase PhaseNum
      | InitialPhase    -- The first phase -- number = infinity!

    instance Outputable CompilerPhase where
       ppr (Phase n)    = int n
       ppr InitialPhase = text "InitialPhase"

    -- See note [Pragma source text]
    data Activation = NeverActive
                    | AlwaysActive
                    | ActiveBefore SourceText PhaseNum
                      -- Active only *strictly before* this phase
                    | ActiveAfter SourceText PhaseNum
                      -- Active in this phase and later
                    deriving( Eq, Data, Typeable )
                      -- Eq used in comparing rules in HsDecls

    data RuleMatchInfo = ConLike                    -- See Note [CONLIKE pragma]
                       | FunLike
                       deriving( Eq, Data, Typeable, Show )
            -- Show needed for Lexer.x

    data InlinePragma            -- Note [InlinePragma]
      = InlinePragma
          { inl_src    :: SourceText -- Note [Pragma source text]
          , inl_inline :: InlineSpec

          , inl_sat    :: Maybe Arity    -- Just n <=> Inline only when applied to n
                                         --            explicit (non-type, non-dictionary) args
                                         --   That is, inl_sat describes the number of *source-code*
                                         --   arguments the thing must be applied to.  We add on the
                                         --   number of implicit, dictionary arguments when making
                                         --   the InlineRule, and don't look at inl_sat further

          , inl_act    :: Activation     -- Says during which phases inlining is allowed

          , inl_rule   :: RuleMatchInfo  -- Should the function be treated like a constructor?
        } deriving( Eq, Data, Typeable )

    data InlineSpec   -- What the user's INLINE pragma looked like
      = Inline
      | Inlinable
      | NoInline
      | EmptyInlineSpec  -- Used in a place-holder InlinePragma in SpecPrag or IdInfo,
                         -- where there isn't any real inline pragma at all
      deriving( Eq, Data, Typeable, Show )
            -- Show needed for Lexer.x

    {-
    Note [InlinePragma]
    ~~~~~~~~~~~~~~~~~~~
    This data type mirrors what you can write in an INLINE or NOINLINE pragma in
    the source program.

    If you write nothing at all, you get defaultInlinePragma:
       inl_inline = False
       inl_act    = AlwaysActive
       inl_rule   = FunLike

    It's not possible to get that combination by *writing* something, so
    if an Id has defaultInlinePragma it means the user didn't specify anything.

    If inl_inline = True, then the Id should have an InlineRule unfolding.

    Note [CONLIKE pragma]
    ~~~~~~~~~~~~~~~~~~~~~
    The ConLike constructor of a RuleMatchInfo is aimed at the following.
    Consider first
        {-# RULE "r/cons" forall a as. r (a:as) = f (a+1) #-}
        g b bs = let x = b:bs in ..x...x...(r x)...
    Now, the rule applies to the (r x) term, because GHC "looks through"
    the definition of 'x' to see that it is (b:bs).

    Now consider
        {-# RULE "r/f" forall v. r (f v) = f (v+1) #-}
        g v = let x = f v in ..x...x...(r x)...
    Normally the (r x) would *not* match the rule, because GHC would be
    scared about duplicating the redex (f v), so it does not "look
    through" the bindings.

    However the CONLIKE modifier says to treat 'f' like a constructor in
    this situation, and "look through" the unfolding for x.  So (r x)
    fires, yielding (f (v+1)).

    This is all controlled with a user-visible pragma:
         {-# NOINLINE CONLIKE [1] f #-}

    The main effects of CONLIKE are:

        - The occurrence analyser (OccAnal) and simplifier (Simplify) treat
          CONLIKE thing like constructors, by ANF-ing them

        - New function coreUtils.exprIsExpandable is like exprIsCheap, but
          additionally spots applications of CONLIKE functions

        - A CoreUnfolding has a field that caches exprIsExpandable

        - The rule matcher consults this field.  See
          Note [Expanding variables] in Rules.hs.
    -}

    isConLike :: RuleMatchInfo -> Bool
    isConLike ConLike = True
    isConLike _            = False

    isFunLike :: RuleMatchInfo -> Bool
    isFunLike FunLike = True
    isFunLike _            = False

    isEmptyInlineSpec :: InlineSpec -> Bool
    isEmptyInlineSpec EmptyInlineSpec = True
    isEmptyInlineSpec _               = False

    defaultInlinePragma, alwaysInlinePragma, neverInlinePragma, dfunInlinePragma
      :: InlinePragma
    defaultInlinePragma = InlinePragma { inl_src = "{-# INLINE"
                                       , inl_act = AlwaysActive
                                       , inl_rule = FunLike
                                       , inl_inline = EmptyInlineSpec
                                       , inl_sat = Nothing }

    alwaysInlinePragma = defaultInlinePragma { inl_inline = Inline }
    neverInlinePragma  = defaultInlinePragma { inl_act    = NeverActive }

    inlinePragmaSpec :: InlinePragma -> InlineSpec
    inlinePragmaSpec = inl_inline

    -- A DFun has an always-active inline activation so that
    -- exprIsConApp_maybe can "see" its unfolding
    -- (However, its actual Unfolding is a DFunUnfolding, which is
    --  never inlined other than via exprIsConApp_maybe.)
    dfunInlinePragma   = defaultInlinePragma { inl_act  = AlwaysActive
                                             , inl_rule = ConLike }

    isDefaultInlinePragma :: InlinePragma -> Bool
    isDefaultInlinePragma (InlinePragma { inl_act = activation
                                        , inl_rule = match_info
                                        , inl_inline = inline })
      = isEmptyInlineSpec inline && isAlwaysActive activation && isFunLike match_info

    isInlinePragma :: InlinePragma -> Bool
    isInlinePragma prag = case inl_inline prag of
                            Inline -> True
                            _      -> False

    isInlinablePragma :: InlinePragma -> Bool
    isInlinablePragma prag = case inl_inline prag of
                               Inlinable -> True
                               _         -> False

    isAnyInlinePragma :: InlinePragma -> Bool
    -- INLINE or INLINABLE
    isAnyInlinePragma prag = case inl_inline prag of
                            Inline    -> True
                            Inlinable -> True
                            _         -> False

    inlinePragmaSat :: InlinePragma -> Maybe Arity
    inlinePragmaSat = inl_sat

    inlinePragmaActivation :: InlinePragma -> Activation
    inlinePragmaActivation (InlinePragma { inl_act = activation }) = activation

    inlinePragmaRuleMatchInfo :: InlinePragma -> RuleMatchInfo
    inlinePragmaRuleMatchInfo (InlinePragma { inl_rule = info }) = info

    setInlinePragmaActivation :: InlinePragma -> Activation -> InlinePragma
    setInlinePragmaActivation prag activation = prag { inl_act = activation }

    setInlinePragmaRuleMatchInfo :: InlinePragma -> RuleMatchInfo -> InlinePragma
    setInlinePragmaRuleMatchInfo prag info = prag { inl_rule = info }

    instance Outputable Activation where
       ppr AlwaysActive       = brackets (text "ALWAYS")
       ppr NeverActive        = brackets (text "NEVER")
       ppr (ActiveBefore _ n) = brackets (char '~' <> int n)
       ppr (ActiveAfter  _ n) = brackets (int n)

    instance Outputable RuleMatchInfo where
       ppr ConLike = text "CONLIKE"
       ppr FunLike = text "FUNLIKE"

    instance Outputable InlineSpec where
       ppr Inline          = text "INLINE"
       ppr NoInline        = text "NOINLINE"
       ppr Inlinable       = text "INLINABLE"
       ppr EmptyInlineSpec = empty

    instance Outputable InlinePragma where
      ppr (InlinePragma { inl_inline = inline, inl_act = activation
                        , inl_rule = info, inl_sat = mb_arity })
        = ppr inline <> pp_act inline activation <+> pp_sat <+> pp_info
        where
          pp_act Inline   AlwaysActive = empty
          pp_act NoInline NeverActive  = empty
          pp_act _        act          = ppr act

          pp_sat | Just ar <- mb_arity = parens (text "sat-args=" <> int ar)
                 | otherwise           = empty
          pp_info | isFunLike info = empty
                  | otherwise      = ppr info

    isActive :: CompilerPhase -> Activation -> Bool
    isActive InitialPhase AlwaysActive      = True
    isActive InitialPhase (ActiveBefore {}) = True
    isActive InitialPhase _                 = False
    isActive (Phase p)    act               = isActiveIn p act

    isActiveIn :: PhaseNum -> Activation -> Bool
    isActiveIn _ NeverActive        = False
    isActiveIn _ AlwaysActive       = True
    isActiveIn p (ActiveAfter _ n)  = p <= n
    isActiveIn p (ActiveBefore _ n) = p >  n

    competesWith :: Activation -> Activation -> Bool
    -- See Note [Activation competition]
    competesWith NeverActive       _                = False
    competesWith _                 NeverActive      = False
    competesWith AlwaysActive      _                = True

    competesWith (ActiveBefore {})  AlwaysActive      = True
    competesWith (ActiveBefore {})  (ActiveBefore {}) = True
    competesWith (ActiveBefore _ a) (ActiveAfter _ b) = a < b

    competesWith (ActiveAfter {})  AlwaysActive      = False
    competesWith (ActiveAfter {})  (ActiveBefore {}) = False
    competesWith (ActiveAfter _ a) (ActiveAfter _ b) = a >= b

    {- Note [Competing activations]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Sometimes a RULE and an inlining may compete, or two RULES.
    See Note [Rules and inlining/other rules] in Desugar.

    We say that act1 "competes with" act2 iff
       act1 is active in the phase when act2 *becomes* active
    NB: remember that phases count *down*: 2, 1, 0!

    It's too conservative to ensure that the two are never simultaneously
    active.  For example, a rule might be always active, and an inlining
    might switch on in phase 2.  We could switch off the rule, but it does
    no harm.
    -}

    isNeverActive, isAlwaysActive, isEarlyActive :: Activation -> Bool
    isNeverActive NeverActive = True
    isNeverActive _           = False

    isAlwaysActive AlwaysActive = True
    isAlwaysActive _            = False

    isEarlyActive AlwaysActive      = True
    isEarlyActive (ActiveBefore {}) = True
    isEarlyActive _                 = False

    -- Used (instead of Rational) to represent exactly the floating point literal that we
    -- encountered in the user's source program. This allows us to pretty-print exactly what
    -- the user wrote, which is important e.g. for floating point numbers that can't represented
    -- as Doubles (we used to via Double for pretty-printing). See also #2245.
    data FractionalLit
      = FL { fl_text :: String         -- How the value was written in the source
           , fl_value :: Rational      -- Numeric value of the literal
           }
      deriving (Data, Typeable, Show)
      -- The Show instance is required for the derived Lexer.x:Token instance when DEBUG is on

    negateFractionalLit :: FractionalLit -> FractionalLit
    negateFractionalLit (FL { fl_text = '-':text, fl_value = value }) = FL { fl_text = text, fl_value = negate value }
    negateFractionalLit (FL { fl_text = text, fl_value = value }) = FL { fl_text = '-':text, fl_value = negate value }

    integralFractionalLit :: Integer -> FractionalLit
    integralFractionalLit i = FL { fl_text = show i, fl_value = fromInteger i }

    -- Comparison operations are needed when grouping literals
    -- for compiling pattern-matching (module MatchLit)

    instance Eq FractionalLit where
      (==) = (==) `on` fl_value

    instance Ord FractionalLit where
      compare = compare `on` fl_value

    instance Outputable FractionalLit where
      ppr = text . fl_text

    {-
    ************************************************************************
    *                                                                      *
        IntWithInf
    *                                                                      *
    ************************************************************************

    Represents an integer or positive infinity

    -}

    -- | An integer or infinity
    data IntWithInf = Int {-# UNPACK #-} !Int
                    | Infinity
      deriving Eq

    -- | A representation of infinity
    infinity :: IntWithInf
    infinity = Infinity

    instance Ord IntWithInf where
      compare Infinity Infinity = EQ
      compare (Int _)  Infinity = LT
      compare Infinity (Int _)  = GT
      compare (Int a)  (Int b)  = a `compare` b

    instance Outputable IntWithInf where
      ppr Infinity = char '∞'
      ppr (Int n)  = int n

    instance Num IntWithInf where
      (+) = plusWithInf
      (*) = mulWithInf

      abs Infinity = Infinity
      abs (Int n)  = Int (abs n)

      signum Infinity = Int 1
      signum (Int n)  = Int (signum n)

      fromInteger = Int . fromInteger

      (-) = panic "subtracting IntWithInfs"

    intGtLimit :: Int -> IntWithInf -> Bool
    intGtLimit _ Infinity = False
    intGtLimit n (Int m)  = n > m

    -- | Add two 'IntWithInf's
    plusWithInf :: IntWithInf -> IntWithInf -> IntWithInf
    plusWithInf Infinity _        = Infinity
    plusWithInf _        Infinity = Infinity
    plusWithInf (Int a)  (Int b)  = Int (a + b)

    -- | Multiply two 'IntWithInf's
    mulWithInf :: IntWithInf -> IntWithInf -> IntWithInf
    mulWithInf Infinity _        = Infinity
    mulWithInf _        Infinity = Infinity
    mulWithInf (Int a)  (Int b)  = Int (a * b)

    -- | Turn a positive number into an 'IntWithInf', where 0 represents infinity
    treatZeroAsInf :: Int -> IntWithInf
    treatZeroAsInf 0 = Infinity
    treatZeroAsInf n = Int n

    -- | Inject any integer into an 'IntWithInf'
    mkIntWithInf :: Int -> IntWithInf
    mkIntWithInf = Int