I'm hitting a runtime error when using what should be safe code under GHCJS. It works correctly with JSaddle. After some time spent trying to minimise the example, I've ended up with this. It's only a few lines, but does depend on prettyprinter - if I get the time, I'll see if I can reproduce the error without that dependency.

Error is:
uncaught exception in Haskell main thread: TypeError: h$RTS_586.d2 is not a function