Playing with Yahoo's stock API in Haskell, use this little program to quickly check stock prices, or change currencies.

stock.hs

import Prelude
import System.Environment
import Network.HTTP
import Control.Monad

showUsage :: IO ()
showUsage = do
        putStrLn "Usage: stock <options...>\n"
        putStrLn "  - get a quote:  stock <symbol>"
        putStrLn "  - change money: stock <from> <to> <amount>"

baseUrl :: String
baseUrl = "http://download.finance.yahoo.com/d/quotes.csv"

-- See http://www.gummy-stuff.org/Yahoo-data.htm
buildStockUrl :: String -> String
buildStockUrl symbol = baseUrl ++ "?s=" ++ (urlEncode symbol) ++ "&f=a"

fetchStockPrice :: String -> IO (Float)
fetchStockPrice url = do
        rsp <- Network.HTTP.simpleHTTP (getRequest url)
        fmap (read . take 256) (getResponseBody rsp) :: IO (Float)

getQuote :: [String] -> IO (Float)
getQuote (symbol:[])    = fetchStockPrice $ buildStockUrl symbol
getQuote (from:to:x:[]) = do
        price <- fetchStockPrice url
        return (price * amount)
        where
          url    = buildStockUrl $ from ++ to ++ "=X"
          amount = read x :: Float

main :: IO ()
main = do
        args <- getArgs
        if length args == 1 || length args == 3
           then getQuote args >>= print
           else showUsage