{-# LANGUAGE DeriveDataTypeable #-}
{-# LANGUAGE GeneralisedNewtypeDeriving #-}
module Language.Haskell.Syntax.Basic where

import Data.Data
import Data.Eq
import Data.Ord
import Data.Bool
import Data.Int (Int)

import GHC.Data.FastString (FastString)
import Control.DeepSeq

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

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

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

{-
************************************************************************
*                                                                      *
Counts and indices
*                                                                      *
************************************************************************
-}

-- | The width of an unboxed sum
type SumWidth = Int

-- | A *one-index* constructor tag
--
-- Type of the tags associated with each constructor possibility or superclass
-- selector
type ConTag = Int

{-
************************************************************************
*                                                                      *
Field Labels
*                                                                      *
************************************************************************
-}

-- | Field labels are just represented as strings;
-- they are not necessarily unique (even within a module)
newtype FieldLabelString = FieldLabelString { field_label:: FastString }
  deriving (Data, Eq, NFData)

{-
************************************************************************
*                                                                      *
Field Labels
*                                                                      *
************************************************************************
-}

-- | See Note [Roles] in GHC.Core.Coercion
--
-- Order of constructors matters: the Ord instance coincides with the *super*typing
-- relation on roles.
data Role = Nominal | Representational | Phantom
  deriving (Eq, Ord, Data)

{-
************************************************************************
*                                                                      *
Source Strictness and Unpackedness
*                                                                      *
************************************************************************
-}

-- | Haskell Bang
--
-- Bangs on data constructor arguments written by the user.
--
-- @(HsBang SrcUnpack SrcLazy)@ and
-- @(HsBang SrcUnpack NoSrcStrict)@ (without StrictData) makes no sense, we
-- emit a warning (in checkValidDataCon) and treat it like
-- @(HsBang NoSrcUnpack SrcLazy)@
--
-- 'GHC.Core.DataCon.HsSrcBang' is a wrapper around this, associating it with
-- a 'GHC.Types.SourceText.SourceText' as written by the user.
-- In the AST, the @SourceText@ is hidden inside the extension point
-- 'Language.Haskell.Syntax.Extension.XBangTy'.
data HsBang =
  HsBang SrcUnpackedness
         SrcStrictness
  deriving Data

-- | Source Strictness
--
-- What strictness annotation the user wrote
data SrcStrictness = SrcLazy -- ^ Lazy, ie '~'
                   | SrcStrict -- ^ Strict, ie '!'
                   | NoSrcStrict -- ^ no strictness annotation
     deriving (Eq, Data)

-- | Source Unpackedness
--
-- What unpackedness the user requested
data SrcUnpackedness = SrcUnpack -- ^ {-# UNPACK #-} specified
                     | SrcNoUnpack -- ^ {-# NOUNPACK #-} specified
                     | NoSrcUnpack -- ^ no unpack pragma
     deriving (Eq, Data)

{-
************************************************************************
*                                                                      *
Fixity
*                                                                      *
************************************************************************
-}

-- | Captures the fixity of declarations as they are parsed. This is not
-- necessarily the same as the fixity declaration, as the normal fixity may be
-- overridden using parens or backticks.
data LexicalFixity = Prefix | Infix deriving (Eq, Data)

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

data Fixity = Fixity Int FixityDirection
  deriving (Eq, Data)