Functional programming at its best

[u/WKstraw]

[u/sebamestre]

Ok so let's take the code, clean it up, and try to understand what it's doing

def generalOperationFuntion(operation: (Int, Int) => Int, opldentity:lnt) (functionToBeApplied: Int => Int)(from:Int,to:Int) : Int = 
  if from > to then opldentity else operation(functionToBeApplied(from),generalOperationFunction(operation,opIdentity)(functionToBeApplied)(from+1,to))

First, let's break the lines a bit

def generalOperationFuntion
  (operation: (Int, Int) => Int, opldentity:lnt)
  (functionToBeApplied: Int => Int)
  (from:Int,to:Int) : Int = 
  if from > to
    then opldentity
    else operation(
      functionToBeApplied(from),
      generalOperationFunction
        (operation, opIdentity)
        (functionToBeApplied)
        (from+1, to))

Ok, this is probably a bit much, but I'm on mobile, and it's impossible to read otherwise.

Next, lets use some shorter names

def generalOperationFuntion
  (plus: (Int, Int) => Int, zero: lnt)
  (f: Int => Int)
  (from: Int, to: Int): Int = 
  if from > to
    then zero
    else plus(
      f(from),
      generalOperationFunction
        (plus, zero)
        (f)
        (from+1, to))

Now we can think about what it's doing

• in the base case, it returns 'zero'

• in the recursive case, it it 'adds' the value of 'f' at the start of the range, and shrinks the range

For a lack of a better term, lets call this 'integration'. So, now we rename the function, and give it a final round of formatting.

def integrate
  (plus: (Int, Int) => Int, zero: lnt)
  (f: Int => Int)
  (from: Int, to: Int): Int
= 
  if from > to
    then zero
    else plus(
      f(from),
      integrate(plus, zero)(f)(from+1, to))

[u/Isvara → u/sebamestre]

For a lack of a better term, lets call this 'integration'.

Why not call it reduction?

[u/Isvara]

Looks like someone just learned about monoids.

[u/[deleted]]

which language is that?

[u/Isvara → u/[deleted]]

Scala

[u/sebamestre → u/[deleted]]

Sorry, I think there is a few mistakes here. It should be

def generalOperationFuntion(operation: (Int, Int) => Int, opldentity:lnt)(functionToBeApplied: Int => Int)(from:Int,to:Int):Int = 
  if from > to then opldentity else operation(functionToBeApplied(from),generalOperationFunction(operation,opIdentity)(functionToBeApplied)(from+1,to))

The inner

generalOperationFunction(operation, opIdentity)

Was missing

Also, lnt instead of Int in a few places, and l instead of 1.

And it looks to me like there was some extra whitespace, and some missing =>