My company's website code is probably about half Haskell (using Yesod, for all the backend code) and half Javascript (for the single-page app frontend). Despite

My company's website code is probably about half Haskell (using Yesod, for all the backend code) and half Javascript (for the single-page app frontend). Despite the nuances described by the author, I really think there is a definite substitution the robust type system vs. unit testing. On the Haskell side, I don't have unit tests, and don't have many tests at all. The number of bugs I discover in the Haskell code is very small in spite of this. I know people have said it before, but when something passes the type checker, most of the time it literally just works. The contrast with the Javascript side couldn't be more stark. The Javascript side is much more challenging to get to a bug-free state, and some of the remaining bugs defy replication, etc. I think to get a system that has a fraction of the reliability afforded by the type system, you really need extensive unit tests. I'm not contradicting the blog author, but I think it's important to keep in mind that in broad strokes, those two aspects really do tradeoff.