Inner (dot) product in tacit point-free form

• pointfree.io

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  A web site for converting haskell code into pointfree haskell code

I'm learning Haskell, coming from the APL family. I'm familiar with point-free style and function composition and wanted to learn Haskell for a more pure functional experience. To get some practice i figured I'd write up the dot product and vector product functions. I haven't begun looking at the vector product, but for dot product I quickly came to `dot a b = sum $ zipWith (*) a b`. After toying around with composition (the B-combinator .), I couldn't get it to work. I looked up the tacit solution in pointfree.io, and it gave me the short and sweet `dot = (sum .) . zipWith (*)`. Now here's my question: how is (sum .) supposed to work? I don't get where the arguments implicitly go or how this makes syntactically sense. What is the order of operations?

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