Function currying

Function currying means converting a function's single parameters list into a multiple parameters list. Take a look at the following code example:

scala> def add(a:Int,b:Int,c:Int) = a + b + c 
add: (a: Int, b: Int, c: Int)Int 
 
scala> add(1,2,3) 
res2: Int = 6 
 
scala> def add(a:Int)(b:Int)(c:Int) = a + b + c 
add: (a: Int)(b: Int)(c: Int)Int 
 
scala> add(1,2,3) 
<console>:16: error: too many arguments (3) for method add: (a: Int)(b: Int)(c: Int)Int 
       add(1,2,3) 
             ^ 
 
scala> add(1)(2)(3) 
res4: Int = 6 

One of the important use cases of currying is to support implicit parameters.

The following examples demonstrate how currying supports implicit parameters:

scala> def add(x: Int, implicit y: Int) = x + y 
<console>:1: error: identifier expected but 'implicit' found. 
       def add(x: Int, implicit y: Int) = x + y 
                       ^ 
 
scala> def add(x: Int) (implicit y: Int) = x + y 
add: (x: Int)(implicit y: Int)Int 
 
scala> implicit val a:Int = 12 
a: Int = 12 
 
scala> add(11) 
res1: Int = 23