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djleonskennedy/haskell-monad-laws.hs

Created February 20, 2018 23:03
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haskell monad laws
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haskell-monad-laws.hs
-- Left identity
-- return x >>= f 'same as' f x
return 3 >>= (\x -> Just (x+100000))
-- Just 100003
(\x -> Just (x+100000)) 3
-- Just 100003
-- Right identity
-- m >>= return 'same as' m
Just "move on up" >>= (\x -> return x)
-- Just "move on up"
[1,2,3,4] >>= (\x -> return x)
-- [1,2,3,4]
putStrLn "Wah!" >>= (\x -> return x)
-- Wah!
-- Associativity
-- (m >>= f) >>= g `same as` m >>= (\x -> f x >>= g)
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