In Standard ML and Haskell, all functions are curried by default -- they take a single argument, and the syntax for defining multiple-argument functions is just

In Standard ML and Haskell, all functions are curried by default -- they take a single argument, and the syntax for defining multiple-argument functions is just sugar for defining single-argument functions that return single-argument functions. That's reflected in this Haskell type signature for a function adding two integers: add :: Int -> Int -> Int This is a function that takes one integer and returns a function which itself takes another integer and then finally returns an integer. Syntax sugar allows you to define it and call it like a single function. An uncurried function in these languages is a function that takes multiple arguments as a tuple. add :: (Int, Int) -> Int You don't see a lot of functions defined this way in Haskell because there isn't really any advantage to doing so in a lazy, pure language. It's more common in Standard ML from what I've seen, because SML is strict and impure.