scala> def sum(a:Int)(b:Int) = a+b; sum: (a: Int)(b: Int)Int scala> var psum = sum(5)_ psum: Int => Int = $$Lambda$1035/814753967@724c5cbe scala> psum(23) res0: Int = 28 The above snippet works fine but not sure why the below snippet complains.I am assuming that if I put underscore for an argument,I can curry that function
scala> def sum(a:Int)(b:Int)(c:Int) = a + b + c; sum: (a: Int)(b: Int)(c: Int)Int scala> var psum = sum(5)_(23) You hit on an ambiguity/limitation of the parser. You can work around it by adding parenthesis
val psum = (sum(5)_)(23) 
def sum(a:Int)(b:Int)(c:Int) = s"a: $a, b: $b, c: $c"; val psum = (sum(5)_)(23); psum(50) == "a: 5, b: 23, c: 50"What you need for this case is val psum = sum(5)(_: Int)(23). (sum(3)_)(2) is calculated as follows: sum(3)_ is the same as (b: Int) => (c: Int) => sum(3)(b)(c) and applying it to 2 gives (c: Int) => sum(3)(2)(c).
If I'm not mistaken, you are looking for partially applied arguments in a function and not for currying. You would have to do it this way:
def sum(a:Int,b:Int,c:Int) = a * b + c sum: (a: Int, b: Int, c: Int)Int sum(10, _:Int, 1) res1: Int => Int = $$Lambda$1131/1517266286@1981d861 res1 (2) res13: Int = 21 This is a limitation of the scala syntax. You can achieve the same semantics like this:
scala> def sum(a:Int)(b:Int)(c:Int) = s"a: $a, b: $b, c: $c" sum: (a: Int)(b: Int)(c: Int)String scala> def flip[A,B,C](f:A => B => C): B => A => C = b => a => f(a)(b) flip: [A, B, C](f: A => (B => C))B => (A => C) scala> flip(sum(5))(23) res1: Int => String = <function1> scala> res1(50) res2: String = a: 5, b: 50, c: 23 Basically, flip switches the order of binary functions, so we can use it make the middle argument b be the last argument of flip(sum(5)).
(*) I took the liberty to make sum give as back a String, which abstracts out any properties that are not relevant to the order functions application, which I interpret as being the core of your question.
