[http://stackoverflow.com/questions/26439889/extension-overloadedstring-doesnt-fully-infer-isstring-why-or-what-am-i-missi](http://stackoverflow.com/questions/26439889/extension-overloadedstring-doesnt-fully-infer-isstring-why-or-what-am-i-missi) ```active haskell {-# LANGUAGE GADTs #-} data A data B a where Foo :: a -> B A main = let x = Foo "ok" in putStrLn "YAY!" ``` ```active haskell {-# LANGUAGE OverloadedStrings #-} {-# LANGUAGE GADTs #-} data A data B a where Foo :: a -> B A main = let x = Foo "ok" in putStrLn "YAY!" ```