haskell - Can't understand result of Monad >> application -


operation >> description following:

sequentially compose 2 actions, discarding value produced first, sequencing operators (such semicolon) in imperative languages.

here example confuses me:

> ([1] ++ [2]) >> ([2] ++ [3]) [2,3,2,3]

i'm expecting list [2,3] result of right part of expression. how can result of [2,3,2,3] explained?

(>>) default defined as

a >> b = >>= (\_ -> b)

so value being ignored a in given monadic value m a. type of >>= specialised list is:

(>>=) :: [a] -> (a -> [b]) -> [b]

l >>= f invokes f each element of list l product list of lists concatenated.

e.g.

[1,2] >>= (\i -> [i, -i]) > [1,-1,2,-2]

ignoring each input element , returning value [2,3] result in n copies of list [2,3] input list of length n

e.g.

[1] >>= (\_ -> [2,3]) > [2,3]  [1,2] >>= (\_ -> [2,3]) > [2,3,2,3]

this second example equivalent ([1] ++ [2]) >> ([2] ++ [3]) in question.


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