Usage example:

GHCi, version 8.0.1: http://www.haskell.org/ghc/  :? for help
Prelude> :l JsonParser.hs
[1 of 1] Compiling JSONParser       ( JsonParser.hs, interpreted )
Ok, modules loaded: JSONParser.
*JSONParser> readJson "test.txt"
Object [("foo",Number 42),("bar",Array [Number 1,Number 2,Bool True,Bool False]),("baz",String "hello world!")]
*JSONParser> :l PrettyJSON.hs
[1 of 3] Compiling Prettify         ( Prettify.hs, interpreted )
[2 of 3] Compiling JSONParser       ( JSONParser.hs, interpreted )
[3 of 3] Compiling PrettyJSON       ( PrettyJSON.hs, interpreted )
Ok, modules loaded: JSONParser, PrettyJSON, Prettify.
*PrettyJSON> let jvalue = renderJSONValue (Object [("foo",Number 42),("bar",Array [Number 1,Number 2,Bool True,Bool False]),("baz",String "hello world!")])
*PrettyJSON> :t jvalue
jvalue :: Doc
*PrettyJSON> putStrLn (compact jvalue)
{"foo": 42,
"bar": [1,
2,
true,
false
],
"baz": "hello world!"
}
*PrettyJSON>