You did nothing wrong, the hundreds of active users due to announcement buzz is a little outside the scope of the sandbox's capabilities, it has some race condition under heavy load. We considered spending time optimizing this in anticipating of the announcement, but more pressing issues took priority. Re-running the line should work.

Seems like a bug to me.

You need to use curly braces in single-line do-expressions:

    do { line <- getLine; putStrLn line }