Because they are more general functions that work on all monads rather
than just lists.
This allows Stream to be defined more flexibly.
On Mon, May 30, 2011 at 9:01 PM, John Ky
Hi all, I'm trying to learn about enumerators by reading this paper and came across some code on page 2 that I found hard to digest, but I think I finally got it:
import Data.Monoid data Stream a = Chunks [a] | EOF deriving (Show, Eq) instance Monad Stream where return = Chunks . return Chunks xs >>= f = mconcat (fmap f xs) EOF >>= _ = EOF instance Monoid (Stream a) where mempty = Chunks mempty mappend (Chunks xs) (Chunks ys) = Chunks (xs ++ ys) mappend _ _ = EOF
I guess, it shows my lack of experience in Haskell, but my question is, why is writing the code this way preferred over say writing it like this:
import Data.Monoid data Stream a = Chunks [a] | EOF deriving (Show, Eq) instance Monad Stream where return x = Chunks [x] Chunks xs >>= f = mconcat (fmap f xs) EOF >>= _ = EOF instance Monoid (Stream a) where mempty = Chunks [] mappend (Chunks xs) (Chunks ys) = Chunks (xs ++ ys) mappend _ _ = EOF
Cheers, -John
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