Haskell dot operator

Question

I try to develop a simple average function in Haskell. This seems to work:

lst = [1, 3]

x = fromIntegral (sum lst)
y = fromIntegral(length lst)

z = x / y

But why doesn't the following version work?

lst = [1, 3]

x = fromIntegral.sum lst
y = fromIntegral.length lst

z = x / y

Answer 1

You're getting tripped up by haskell's precedence rules for operators, which are confusing.

When you write

x = fromIntegral.sum lst

Haskell sees that as the same as:

x = fromIntegral.(sum lst)

What you meant to write was:

x = (fromIntegral.sum) lst