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danking/gist:22270f0d20418a6ec660

Created April 26, 2015 19:46
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gistfile1.hs
instance Monoid a => Monoid [(Either a b)] where
mempty = []
mappend [] vs = vs
mappend vs [] = vs
mappend [(Left v1)] ((Left v2):vs) = (Left $ mappend v1 v2):vs
mappend (v1:v2:vs) vs' = v1 : (mappend (v2:vs) vs')
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