- Currying is different from Partial (Function) Application.
- In Scala, it is possible to define a function that returns another function which can be called with arguments. Although this might look similar, it is not necessarily the same thing as either Currying or Partial (Function) Application.
- What is currying? It is a process whereby the multiple arguments required by a function are passed in, one at a time, instead of the typical process of calling the function by supplying all its arguments at once.
val volume = (length: Double, breadth:Double, height: Double) => length * breadth * height // called with the required argument at once volume(1,2,3) // creates a curried version of the function val curriedVersion = volume.curried // with the curried version we can pass in the arguments one after the other // pass first argument val withFirstArg = curriedVersion(1) // and now with second argument val withFirstArgAndSecondArg = withFirstArg(2) // and now with third argument which yields the result val volumeValue: Double = withFirstArgAndSecondArg(3)
- Partial Application what is it? It is possible to take a function that expects multiple arguments and pre-fill some of these arguments. Doing this, returns a function that can then be called by supplying the remaining argument(s) that were not pre-filled.
val volume = (length: Double, breadth:Double, height: Double) => length * breadth * height // called with the required argument at once volume(1,2,3) // first and second argument pre-filled val withFirstAndSecondArgsSet: (Double) => Double = volume(1,2,_) // now third argument is supplied and result evaluated val volumeValue: Double = withFirstAndSecondArgsSet(3)
- Currying can then be seen as a specialised outcome of Partial Application. The resulting function of Partial Application can have any number of arguments. With Currying it has to be a chained sequence of functions that take one argument at a time.
- Currying can also be seen as a sequence of Partial Application where each step involves partially applying only one of all possible arguments defined by the function.
- Partial (Function) Application is different from partial functions.