This is my implementation of the modulo operator. The function first checks to see if the result is positive. If it is, it generates a new dividend by subtracting the divisor, thereby narrowing down to the remainder, which will be left in the dividend.

modulo.scala

def modulo(dividend: Int, divisor: Int): Int = {
  if (dividend / divisor > 0) modulo(dividend - divisor, divisor) else dividend
}

def %(money: Int, coin: Int): Int = {
  money % coin
}

println(%(4, 3))
println(modulo(4, 3))

/*
1
1
*/