First Class Functions - Ruby, JavaScript & Scala

Aug 18 2013

This has been a good week, thanks to the public holiday calendar in India I got a six day break by taking a couple of days off in between a weekend and two national holidays.

So I utilized the time and rebuilt http://biblefind.in with Scala and Angular.js. I spent a day also building a Ruby gem. The only thing missing was to write a blog to make this a productive holiday.

So in this small post let us look as "first class functions" or passing functions as arguments in the three languages I like Ruby, JavaScript and Scala.

Our idea is simple, we want to pass a function, two operands and the function on which will be applied on the operands. So if I pass 2, 3 and a product function I should get 6.

Let's start with Ruby -

module Calculate
  def self.do(a, b, operation)
    operation.call(a, b)
  end
end

#execute it, with a lambda
Calculate.do(2, 3, ->(a, b){a + b}) #5
Calculate.do(2, 3, ->(a, b){a * b}) #6

#or use a Proc
Calculate.do(2, 3, Proc.new{|a, b|a * b})

Pretty decent, let's do this in JavaScript or rather in CoffeScript to avoid the prototype syntax -

class Calculate
  @do: (a, b, operation) ->
    operation(a, b)

#execute it
Calculate.do(9, 3, (a, b) -> a + b) #12
Calculate.do(9, 3, (a, b) -> a * b) #27

CoffeeScript and Ruby lambda's "stabby" syntax is quite similar, so similar that is messes with my head. I wish they were exactly same but then I am no authority to complain.

Finally, let's do this in Scala -

object Calculate {
  def apply(a: Int, b: Int)(operation: (Int, Int) => Int) = {
    operation(a, b)
   }
}

//execute it
def add(a: Int, b: Int) = { a + b }
Calculate(2, 3)(add) //5

//can we do better?
//yes, create a partially applied, anonymous function
Calculate(2, 3){ _ * _ } //6
Calculate(2, 3){ _ + _ } //5

So we see Scala provides us more powerful constructs like partially applied functions but makes the code a bit cryptic to new-comers. Scala code is more verbose but then again it provides us with type safety.

Anyways, not to get into any language wars, I think all three languages are fun to work with and have really good frameworks for productivity. Happy programming.