[Haskell-cafe] Monad Description For Imperative Programmer

ok ok at cs.otago.ac.nz
Thu Aug 2 00:04:29 EDT 2007

Someone asked about comparing monads to loops.

If you are chiefly familiar with the i/o and state monads, that doesn't
really make a lot of sense, but there IS a use of monads which IS a kind
of loop.

Only yesterday I was trying to read someone else's Haskell code where
they had imported Control.Monad for the sake of >>= and liftM2.  And
how were they using >>= and liftM2?

  - they were using >>= on lists, where it means the same as concatMap

     To a beginner, I suggest that (concatMap f xs) is clearer than
     (xs >>= f)

  - they were using (liftM2 f xs ys) on lists, where it means the same
	[f x y | x <- xs, y <- ys]

No doubt there are people who find the monadic versions clearer.
However, since the monadic operations *ARE* loops when applied to lists,
it could very easily give rise to the misunderstanding that monads have
something to do with looping.

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