It's impossible to tell if someone is being sarcastic on the internet, because no matter how stupid your comment is at face value, there's always a percentage of people on the forum stupid enough to say it in earnest.

https://en.wikipedia.org/wiki/Poe%27s_law

Use a winking smiley face emoticon ;-) or /s

But I was smiling when I wrote my comment, isn't that enough?

With the number of fanatics of Haskell and functional programming on HN, it's completely reasonable to think you were serious with your comment.