FloatingOrIntegral.hs

-- This is an alternative solution to the problem discussed in the video https://www.youtube.com/watch?v=WplTbki3gCg

{-# LANGUAGE RankNTypes, StandaloneDeriving, DeriveAnyClass, TypeApplications, ScopedTypeVariables, GADTs #-}

import Data.Scientific
import Type.Reflection

data AnyRealFloat = AnyRealFloat (forall a. RealFloat a => a)

instance Eq AnyRealFloat where
instance Ord AnyRealFloat where
instance Num AnyRealFloat where
instance Fractional AnyRealFloat where
  fromRational x = AnyRealFloat $ fromRational x
instance Floating AnyRealFloat where
instance Real AnyRealFloat where
instance RealFrac AnyRealFloat where
instance RealFloat AnyRealFloat where

data AnyIntegral = AnyIntegral (forall a. Integral a => a)

instance Eq AnyIntegral where
instance Ord AnyIntegral where
instance Num AnyIntegral where
  fromInteger x = AnyIntegral $ fromInteger x
  AnyIntegral x * AnyIntegral y = AnyIntegral (x * y)
instance Real AnyIntegral where
instance Enum AnyIntegral where
instance Integral AnyIntegral where

convertScientific :: forall t. Typeable t => Scientific -> t
convertScientific sci = case floatingOrInteger sci of
  Left (AnyRealFloat floating)
    | Just HRefl <- typeRep @t `eqTypeRep` typeRep @Float -> floating
    | Just HRefl <- typeRep @t `eqTypeRep` typeRep @Double -> floating
  Right (AnyIntegral integer)
    | Just HRefl <- typeRep @t `eqTypeRep` typeRep @Int -> integer
    | Just HRefl <- typeRep @t `eqTypeRep` typeRep @Integer -> integer