use context essentials2021
fun single-pen-cost-1(message):
    0.25 + (0.02 * string-length(message))
end

# with type annotations:
fun single-pen-cost-2(message :: String) -> Number:
  0.25 + (0.02 * string-length(message))
end

# with examples:
fun single-pen-cost-3(message :: String) -> Number:
  0.25 + (0.02 * string-length(message))
where:
  single-pen-cost-3("a") is 0.27
  single-pen-cost-3("Brown") is 0.35
  single-pen-cost-3("CSCI0111") is 0.25 + (0.02 * 8)
end

fun pen-cost(num-pens :: Number, message :: String) -> Number:
  doc: "Calculates the cost of buying num-pens number of pens, at $0.25 per pen + $0.02 for each character in the message"
  num-pens * (0.25 + (0.02 * string-length(message)))
where:
  pen-cost(1, "Brown") is 0.35
end