Ranges

Ranges use the x..y syntax and are a form of sequence. Bounded ranges are finite (seq), while unbounded ranges are potentially infinite (gen).

for 1..5 | i -> println("Hello times {i}")

def naturalNumbers = 0..

def oneToTen = 1..10

Types and ranges

Any type can be used in a range if it supports succ and comparison:

def aToZ = 'a'..'z'

type Point = (x: int, y: int)

def Point.succ(p: Point) -> Point(p.x + 1, p.y + 1)

def Point.`<=`(p1: Point, p2: Point) -> magnitude(p1) <= magnitude(p2)

def points = Point(1, 1)..Point(8, 8)

Implementing ranges

You can implement your own range generator when you have succ and a comparison:

def range
  : [(succ: a -> a, `<=`: (a, a) -> bool)] (start: a, end: a) -> seq(a)
  = { start, end ->
      seq {
        memory {
          def current = mut start

          while current <= end ->
            yield current
            current := succ(current)
        }
      }
    }