Random Capability Passing Style

rand.scala

package rand

import scala.util.Random

type Rand[A] = Random ?=> A

inline def apply[A](body: Rand[A]): A = body(using new Random)

val int: Rand[Int] = r ?=> r.nextInt

val bool: Rand[Boolean] = r ?=> r.nextBoolean

def range(min: Int, max: Int): Rand[Int] =
  val intervalLength = max.toLong - min.toLong
  val totalLength    = (Int.MaxValue.toLong - Int.MinValue.toLong).toDouble

  ((int - Int.MinValue.toLong) / totalLength * intervalLength + min).toInt

val lowerAscii: Rand[Char] = range('a'.toInt, 'z'.toInt).toChar

val upperAscii: Rand[Char] = range('A'.toInt, 'Z'.toInt).toChar

val digit: Rand[Char] = range('0'.toInt, '9'.toInt).toChar

def oneOf[A](rands: Rand[A]*): Rand[A] = rands(range(0, rands.length))

val alpha: Rand[Char] = oneOf(lowerAscii, upperAscii)

val alphaNum: Rand[Char] = oneOf(lowerAscii, upperAscii, digit)

def listOfN[A](n: Int, ra: Rand[A]): Rand[List[A]] =
  if n <= 0 then Nil
  else ra :: listOfN(n - 1, ra)

def list[A](size: Rand[Int], ra: Rand[A]): Rand[List[A]] =
  listOfN(size, ra)

def identifier: Rand[String] =
  (oneOf(alpha) :: list(range(0, 9), alphaNum)).mkString