Scotty web service to convert currencies in Haskell

I need to create a web service to convert between different currencies using the scotty web framework in Haskell.

The web service should respond to get requests such as /convert/15?to=usd&from=eur.

I have this code so far:

{-# LANGUAGE OverloadedStrings #-}

import Web.Scotty
import Data.Monoid (mconcat)

functionxs :: a -> Int
functionxs a = 5

main = scotty 3000 $ do
  get "/:word" $ do
    name <- param "word"
    html $ mconcat ["<h1>Hi, ", greeting, " what's up!</h1>"]

Thus, when you execute in the browswer: http://localhost:3000/Tony the result is: Hi, Tony, what's up!

The problem is that I don't know how to change the code in order to have '/convert/15?to=usd&from=eur.' as request and get the proper answer.

Hopefully anyone can help me.

Thanks in advance.