comment-under-the-last-guard.hs

module Tariff.Zone where

zoneOf :: Double -> Int
zoneOf distance = case distance of
   d
     | d > 10    -> 3
     | d > 5     -> 2
       -- short trips are all zone 1
   _ -> 1

fare :: Int -> Int
fare zone
    | zone > 2  = 4
    | otherwise =
        let base = 2
         in base + zone
    -- the base fare has not changed since the last review

surcharge :: Int
surcharge = 1