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markus1189/switch.hs

Created January 30, 2016 14:36
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Haskell LightSwitch
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switch.hs
{-# LANGUAGE GADTs #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE DataKinds #-}
module LightSwitch where
data Power = On | Off
type family Toggle (a :: Power) where
Toggle On = Off
Toggle Off = On
data Switch (a :: Power) where
Switch :: Switch a
on :: Switch On
on = Switch
off :: Switch Off
off = Switch
toggle :: Switch a -> Switch (Toggle a)
toggle Switch = Switch
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