terrelcodes

fun code-point-to-hex-digit( d :: Number ) -> Number:
  doc: "convert a code point (letter) to a hex digit"
  ask:
    | (d >= 48) and (d <= 57) then: d - 48
    | (d >= 97) and (d <= 103) then: d - 87
    | (d >= 65) and (d <= 71) then: d - 55
  end       
where:
  code-point-to-hex-digit(string-to-code-point('0')) is 0