{-| Copyright : (C) 2018, Google Inc. License : BSD2 (see the file LICENSE) Maintainer : Christiaan Baaij <christiaan.baaij@gmail.com> Using /ANN/ pragma's you can tell the Clash compiler to use a custom bit representation for a data type. See @DataReprAnn@ for documentation. -} {-# LANGUAGE RankNTypes #-} {-# LANGUAGE StandaloneDeriving #-} {-# LANGUAGE TemplateHaskell #-} {-# OPTIONS_GHC -Wno-orphans #-} module Clash.Annotations.BitRepresentation ( -- * Data structures to express a custom bit representation DataReprAnn(..) , ConstrRepr(..) -- * Convenience type synonyms for Integer , BitMask , Value , Size , FieldAnn -- * Functions , liftQ ) where import Data.Data (Data) import Data.Typeable (Typeable) import Language.Haskell.TH.Instances () import qualified Language.Haskell.TH.Lift () import qualified Language.Haskell.TH.Syntax as TH import GHC.Generics (Generic) type BitMask = Integer type Value = Integer type Size = Int -- | BitMask used to mask fields type FieldAnn = BitMask -- | Lift values inside of 'TH.Q' to a Template Haskell expression liftQ :: TH.Lift a => TH.Q a -> TH.Q TH.Exp liftQ :: Q a -> Q Exp liftQ = (Q a -> (a -> Q Exp) -> Q Exp forall (m :: Type -> Type) a b. Monad m => m a -> (a -> m b) -> m b >>= a -> Q Exp forall t. Lift t => t -> Q Exp TH.lift) -- NOTE: The following instances are imported from Language.Haskell.TH.Lift. -- This module also implements 'instance Lift Exp', which might make debugging -- template haskell more difficult. Please uncomment these instances and the -- import of TH.Lift whenever it suits you. -- --deriving instance TH.Lift TH.Name --deriving instance TH.Lift TH.OccName --deriving instance TH.Lift TH.NameFlavour --deriving instance TH.Lift TH.ModName --deriving instance TH.Lift TH.NameSpace --deriving instance TH.Lift TH.PkgName -- | Annotation for custom bit representations of data types -- -- Using /ANN/ pragma's you can tell the Clash compiler to use a custom -- bit-representation for a data type. -- -- For example: -- -- @ -- data Color = R | G | B -- {-# ANN module (DataReprAnn -- $(liftQ [t|Color|]) -- 2 -- [ ConstrRepr 'R 0b11 0b00 [] -- , ConstrRepr 'G 0b11 0b01 [] -- , ConstrRepr 'B 0b11 0b10 [] -- ]) #-} -- @ -- -- This specifies that @R@ should be encoded as 0b00, @G@ as 0b01, and -- @B@ as 0b10. The first binary value in every @ConstrRepr@ in this example -- is a mask, indicating which bits in the data type are relevant. In this case -- all of the bits are. -- -- Or if we want to annotate @Maybe Color@: -- -- @ -- {-# ANN module ( DataReprAnn -- $(liftQ [t|Maybe Color|]) -- 2 -- [ ConstrRepr 'Nothing 0b11 0b11 [] -- , ConstrRepr 'Just 0b00 0b00 [0b11] -- ] ) #-} -- @ -- -- By default, @Maybe Color@ is a data type which consumes 3 bits. A single bit -- to indicate the constructor (either @Just@ or @Nothing@), and two bits to encode -- the first field of @Just@. Notice that we saved a single bit by exploiting -- the fact that @Color@ only uses three values (0, 1, 2), but takes two bits -- to encode it. We can therefore use the last - unused - value (3), to encode -- one of the constructors of @Maybe@. We indicate which bits encode the -- underlying @Color@ field of @Just@ by passing /[0b11]/ to ConstrRepr. This -- indicates that the first field is encoded in the first and second bit of the -- whole datatype (0b11). -- -- __NB__: BitPack for a custom encoding can be derived using -- 'Clash.Annotations.BitRepresentation.Deriving.deriveBitPack'. data DataReprAnn = DataReprAnn -- Type this annotation is for: TH.Type -- Size of type: Size -- Constructors: [ConstrRepr] deriving (Int -> DataReprAnn -> ShowS [DataReprAnn] -> ShowS DataReprAnn -> String (Int -> DataReprAnn -> ShowS) -> (DataReprAnn -> String) -> ([DataReprAnn] -> ShowS) -> Show DataReprAnn forall a. (Int -> a -> ShowS) -> (a -> String) -> ([a] -> ShowS) -> Show a showList :: [DataReprAnn] -> ShowS $cshowList :: [DataReprAnn] -> ShowS show :: DataReprAnn -> String $cshow :: DataReprAnn -> String showsPrec :: Int -> DataReprAnn -> ShowS $cshowsPrec :: Int -> DataReprAnn -> ShowS Show, Typeable DataReprAnn DataType Constr Typeable DataReprAnn => (forall (c :: Type -> Type). (forall d b. 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