haskell - Writing in pointfree style f x = g x x

Question

I am learning Haskell. I'm sorry for asking a very basic question but I cant seem to find the answer. I have a function f defined by :

f x = g x x

where g is an already defined function of 2 arguments. How do I write this pointfree style? Edit : without using a lambda expression.

Thanks

Answer 1

f can be written with Control.Monad.join:

f = join g

join on the function monad is one of the primitives used when constructing point-free expressions, as it cannot be defined in a point-free style itself (its SKI calculus equivalent, SII — ap id id in Haskell — doesn't type).