monoid.gby1 Monoid 2012.11.18 2 (a b) c = a (b c) Monoid (a b) c = a (b c) e a = a e = a (a b) c = a (b c) e a = a e = a a a-1 = e Semi ring fusion 3 Q) Monoid A) 1 Monoid 4 Monoid doctest data Summary = Summary { sExamples :: Int , sTried :: Int , sErrors :: Int , sFailures :: Int } deriving Eq instance Monoid Summary where mempty = Summary 0 0 0 0 (Summary x1 x2 x3 x4) ‘mappend‘ (Summary y1 y2 y3 y4) = Su
