[Haskell-cafe] What's the advantage of writing Haskell this way?

[John Ky]

Hi all,

I'm trying to learn about enumerators by reading this
paper<https://john-millikin.com/downloads/enumerator_0.4.10.pdf>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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