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Add Function instance to Comonad to match Extend instance #82

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Add Function instance to Comonad to match Extend instance #82

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4 changes: 4 additions & 0 deletions src/Control/Comonad.purs
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Expand Up @@ -7,6 +7,7 @@ module Control.Comonad
import Control.Extend (class Extend, duplicate, extend, (<<=), (=<=), (=>=), (=>>))

import Data.Functor (class Functor, map, void, ($>), (<#>), (<$), (<$>))
import Data.Monoid (class Monoid, mempty)

-- | `Comonad` extends the `Extend` class with the `extract` function
-- | which extracts a value, discarding the comonadic context.
Expand All @@ -19,3 +20,6 @@ import Data.Functor (class Functor, map, void, ($>), (<#>), (<$), (<$>))
-- | - Right Identity: `extract (f <<= xs) = f xs`
class Extend w <= Comonad w where
extract :: forall a. w a -> a

instance comonadFn :: Monoid m => Comonad ((->) m) where
extract f = f mempty