How does Haskell evaluate expression

Question

How come that this works

> (* 30) 4
120

but this doesn't

> * 30 40
error: parse error on input ‘*’

Answer 1

(* 30) is a section, which still treats * as a binary (infix) operator, just one that's missing an argument, short for (\x -> x * 30). The parentheses themselves are part of the syntax, rather than being the explicit (but redundant) parentheses you can wrap around an arbitrary expression.

You can think of (*) as a degenerate section that is missing both arguments. You cannot otherwise use an infix operator in the prefix position without using parentheses.