How does function application with the $ operator curry in Haskell?

Question

I am learning haskell and am a little confused how the function application operator $ curry\'s.

According to GHC the type of $ is

*Main>:t ($)
(         


        

Answer 1

Infix operators have special rules. See this page: http://www.haskell.org/haskellwiki/Section_of_an_infix_operator

Basically, since $ is an infix operator, ($ 2) actually fixes 2 as the second argument of $, so it is equivalent to flip ($) 2.

The idea is to make partial application with operators more intuitive, so for example if you map (/ 2) over a list, you can imagine putting each element of the list in the "missing" spot on the left side of the division sign.

If you want to use your curry_test function this way, you could do

let x = (`curry_test` "123")