Create an array with all numbers from min to max without a loop

Question

I have two numbers, min and max, and I want to create an array that contains all number between them (including min and max).

The most obvious approach is to use a for loop for this, and push the single values onto an array. Nevertheless, this seems to be a quite naive approach, i.e. it's imperative programming.

Now I was thinking of how to create such an array in a more functional style. Basically, something such as the reverse of a reduce function: Instead of reducing an array to a number, building up an array from two numbers.

How could I do this? What is a functional approach to solve this problem?

Basically, I'm thinking of something such as 10..20 in some other languages. What's the most elegant equivalent for this in JavaScript?

Answer 1

You can think of a "functional" definition of range:

range(low, hi) = [], if low > hi
range(low, hi) = [low] (+) range(low+1,hi), otherwise,

which leads to the JS definition:

function range(low,hi){
  function rangeRec(low, hi, vals) {
     if(low > hi) return vals;
     vals.push(low);
     return rangeRec(low+1,hi,vals);
  }
  return rangeRec(low,hi,[]);
}