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{-# LANGUAGE UndecidableInstances #-}

module Feldspar.Core.Constructs.Conversion
    ( Conversion (..)
    ) where

import Language.Syntactic
import Language.Syntactic.Interpretation.Semantics
import Language.Syntactic.Constructs.Binding

import Feldspar.Range
import Feldspar.Lattice
import Feldspar.Core.Types
import Feldspar.Core.Interpretation

data Conversion a
  where
    F2I     :: (Type a, Integral a) => Conversion (Float :-> Full a)
    I2N     :: (Type a, Type b, Integral a, Num b
               ,Size a ~ Range a
               ) =>
               Conversion (a :-> Full b)
    B2I     :: (Type a, Integral a) => Conversion (Bool  :-> Full a)
    Round   :: (Type a, Integral a) => Conversion (Float :-> Full a)
    Ceiling :: (Type a, Integral a) => Conversion (Float :-> Full a)
    Floor   :: (Type a, Integral a) => Conversion (Float :-> Full a)

rangeToSize :: Lattice (Size a) => TypeRep a -> Range Integer -> Size a
rangeToSize (IntType _ _) r = rangeProp r
rangeToSize _ _             = universal

rangeProp :: forall a . (Bounded a, Integral a) => Range Integer -> Range a
rangeProp (Range l u)
    | withinBounds l && withinBounds u
        = range (fromIntegral l) (fromIntegral u)
    | otherwise = range minBound maxBound
  where withinBounds i = toInteger (minBound :: a) <= i &&
                         i <= toInteger (maxBound :: a)

instance WitnessCons Conversion
  where
    witnessCons F2I     = ConsWit
    witnessCons I2N     = ConsWit
    witnessCons B2I     = ConsWit
    witnessCons Round   = ConsWit
    witnessCons Ceiling = ConsWit
    witnessCons Floor   = ConsWit

instance WitnessSat Conversion
  where
    type SatContext Conversion = TypeCtx
    witnessSat F2I     = SatWit
    witnessSat I2N     = SatWit
    witnessSat B2I     = SatWit
    witnessSat Round   = SatWit
    witnessSat Ceiling = SatWit
    witnessSat Floor   = SatWit

instance MaybeWitnessSat TypeCtx Conversion
  where
    maybeWitnessSat = maybeWitnessSatDefault

instance Semantic Conversion
  where
    semantics F2I     = Sem "f2i"     truncate
    semantics I2N     = Sem "i2n"     (fromInteger.toInteger)
    semantics B2I     = Sem "b2i"     (\b -> if b then 1 else 0)
    semantics Round   = Sem "round"   round
    semantics Ceiling = Sem "ceiling" ceiling
    semantics Floor   = Sem "floor"   floor

instance ExprEq   Conversion where exprEq = exprEqSem; exprHash = exprHashSem
instance Render   Conversion where renderPart = renderPartSem
instance Eval     Conversion where evaluate = evaluateSem
instance ToTree   Conversion
instance EvalBind Conversion where evalBindSym = evalBindSymDefault
instance Sharable Conversion

instance AlphaEq dom dom dom env => AlphaEq Conversion Conversion dom env
  where
    alphaEqSym = alphaEqSymDefault

instance SizeProp Conversion
  where
    sizeProp F2I     _ = universal
    sizeProp i2n@I2N (WrapFull a :* Nil)
        = rangeToSize (resultType i2n) (mapMonotonic toInteger (infoSize a))
    sizeProp B2I     _ = universal
    sizeProp Round   _ = universal
    sizeProp Ceiling _ = universal
    sizeProp Floor   _ = universal

instance (Conversion :<: dom, Optimize dom dom) => Optimize Conversion dom
  where
    constructFeatOpt i2n@I2N (a :* Nil)
        | Just TypeEq <- typeEq (resultType i2n) (infoType $ getInfo a)
        = return a
    constructFeatOpt a args = constructFeatUnOpt a args

    constructFeatUnOpt = constructFeatUnOptDefault