In Rust and Haskell you have to at least annotate the parameter types and return type of functions.

In OCaml type inference is a lot more powerful: you don’t have to annotate function signatures

Actually, Haskell and OCaml have this in common. Only Rust requires parameter types of the three.

I could do

add2 a b = a + b
main = do
    putStrLn $ "5 + 3 = " ++ (show $ add2 5 3)

And that would work