[Haskell-cafe] Why this doesn't work?

27 Apr 2014

      Hi Cafe,

I don't understand why this doesn't work:

import qualified Data.Vector.Generic as G
import Control.Monad.ST

test :: G.Vector v a => v a -> v a
test x = runST . (>>= G.freeze) . G.thaw $ x

But if I replace "." with "$", it can compile.

test x = runST $ (>>= G.freeze) . G.thaw $ x

I originally though f $ g x can always be written as f . g $ x

Kai Zhang