A while ago I decided that in order to learn Haskell I should make an attempt to stop reaching for Python whenever I needed to solve a “small problem” and use Haskell instead. This morning I found a need to unescape URLs inside Vim and I didn’t catch myself until after I had written the following Python code:

#! /usr/bin/env python

import urllib
import sys

for l in sys.stdin:
    print urllib.unquote(l),

After a little bit of cursing I started browsing Hoogle and after bit of searching I found the Network.URI module. My Haskell solution ended up looking like this:

module Main where

import Network.URI

main :: IO ()
main = interact $ unlines . (map unEscapeString) . lines

Short, sweet, and easy to understand, I think.

In case you want to go the other direction, i.e. to escape strings in Haskell then combining escapeURIString and isUnreserved is the right thing to do.