nim-by-example/content/types/range.md

title
Range Types

Range Types

Range types that guarantee a value will always be within a given range also exist. Whenever possible, out-of-bounds values will fail at compile-time, otherwise they will fail at run-time.

type
  TwoDigits* = range[10..99]

let a = 2
var b: TwoDigits = 99 + a  # Fails at run-time
let c: TwoDigits = 100  # Fails at compile-time

Also note that range types also work on any other ordinal type, so a range over an enum is also valid:

type
  MyEnum = enum
    A, B, C, D, E
  BToD = range[B..D]

let value: BToD = C