[Haskell-cafe] Usage of . and $

[Jefferson Heard]

Usually, I can do this, but today, my brain is weak, and I'm just trying to 
get this piece of code out the door.  My code looks like this:

weight = sum (IntMap.elems (IntMap.intersectionWith 
		     (\x y -> x*y) queryVector rationalProjection)) 

I know that this will work (ignoring indentation):

sum $ IntMap.elems $ IntMap.intersectionWith (\x y -> x*y) queryVector 
rationalProjection

But why won't this?:

sum . IntMap.elems . IntMap.IntersectionWith ...

Is there a difference between the "elegance" of function composition versus 
application?