Functors in fsharp

functor.fs

 type SumFunctor<'T> = {
      sumFn : 'T -> 'T -> 'T
      diffFn : 'T -> 'T -> 'T
  }

  let createSumFunctor monoidOp negMonoidOp =
      {
          sumFn = monoidOp
          diffFn = negMonoidOp
      }

  let sumable { sumFn = sumFn } a =
      sumFn a a

  let sum1 (a : float) =
      let s : SumFunctor<float> = createSumFunctor (+) (-)
      sumable s a

  let sum2 (a : int) =
      let s : SumFunctor<int> = createSumFunctor (+) (-)
      sumable s a