ios.e-legion.com test task

test.hs

import Maybe
import Data.List
import Text.XML.Light

main :: IO()
main = readFile "test.xml" >>= putStrLn . solve

solve :: String -> String
solve = formatResult . getTotal . reduce . getList

type Category = String
type Price = Float

getList :: String -> [(Category, Price)]
getList = pairs . items . orders . parseXMLDoc
    where name n = QName n Nothing Nothing
          orders (Just doc) = findElements (name "order") doc
          items = foldl (\ x y -> x ++ findElements (name "item") y) []
          pairs = foldl (\ x y -> pair y : x) []
          pair x = (fromJust $ findAttr (name "type") x,
             read $ fromJust $ findAttr (name "price") x :: Float)

reduce :: [(Category, Price)] -> [(Category, Price)]
reduce = foldl f []
    where f xs x@(c, p) = add xs x $ findIndex ((c ==) . fst) xs
          add xs x Nothing  = x : xs
          add xs x (Just n) = let y = xs !! n in (new x y : delete n xs)
          new x y = (fst x, snd x + snd y)
          delete n xs = let (ys, zs) = splitAt n xs in ys ++ (tail zs)

getTotal :: [(Category, Price)] -> ([(Category, Price)], Price)
getTotal xs = (xs, foldl ((. snd) . (+)) 0 xs)

formatResult :: ([(Category, Price)], Price) -> String
formatResult (xs, t) = f xs ++ "Total: " ++ show t
    where f []          = "\n"
          f ((c, p):xs) = c ++ ": " ++ show p ++ "\n" ++ f xs   

test.xml

<?xml version="1.0" encoding="UTF-8"?>
<ordersList>
    <order id="1" totalPrice="150.00">
        <item price="100.00" title="Помидоры" type="Овощи" weight="2" units="kg"/>
        <item price="50.00" title="Кока-кола" type="Напитки" quantity="2"/>
    </order>
    <order id="2" totalPrice="120.00">
        <item price="70.00" title="Огурцы" type="Овощи" weight="1" units="kg"/>
        <item price="50.00" title="Кока-кола" type="Напитки" quantity="2"/>
    </order>
    <order id="3" totalPrice="300.00">
        <item price="140.00" title="Огурцы" type="Овощи" weight="2" units="kg"/>
        <item price="60.00" title="Пепси" type="Напитки" quantity="1"/>
        <item price="100.00" title="Вертолёт" type="Игрушки" quantity="1"/>
    </order>
</ordersList>