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Dannyu NDos <[hidden email]>Date: 2019년 8월 7일 (수) 04:50
Subject: Re: Add instance Monoid ((f :+: g) a)
To: Haskell Libraries <
[hidden email]>
Ah, sorry. (:+:) is not an Applicative. It's still possible to make instance Monoid:
instance Semigroup (f a) => Semigroup ((f :+: g) a) where
InL x <> InL y = InL (x <> y)
InL _ <> y = y
x <> _ = x
instance Monoid (f a) => Monoid ((f :+: g) a) where
mempty = InL mempty
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