> Aside from the learning curve, there were several bugs in one of the Haskell libraries that caused frequent outages (until we were able to pinpoint what was wrong),
What was the bug and what was the library?
What was the bug and what was the library?
For what it's worth, this bug was an outlier. The pitfalls of unsafePerformIO are relatively well-known.
For contrast, there a bug in PHP's opcode cache that causes memory corruption in our setup. The best we've managed to do to deal with that by patching PHP to bump the refcount of some object to a billion. The failure condition is sufficiently obscure that it took us multiple man-months to figure that much out.