traverse.lhs

Given common usage of map, then sequence, with the
following signatures.

> sequence :: (Monad m) => [m a] -> m [a]
> map :: (a -> b) -> [a] -> [b]

e.g. 
> x :: (Monad m) => [m a]
> x = map readFile ["file1.txt", "file2.txt"]

> y :: (Monad m) => m [a]
> y = sequence x

You can take anything fitting this pattern and replace with a traverse (called mapM in the standard haskell library):


> traverse :: (Monad m) => (a -> m b) -> [a] -> m [b]
> traverse f as = sequence (map as)

e.g.
> z :: (Monad m) => m [a]
> z = traverse readFile ["file1.txt", "file2.txt"