Haskell does not eliminate side effects. It allows you to control them.<p>You do realize that system you described - Facebook&#x27;s Sigma - is a real-time, massively concurrent online spam-fighting system, that automatically and implicitly makes your code concurrent for all operations, can optimize it, and has automated caching&#x2F;batching request mechanisms in place to talk to external systems (Graph databases, SQL, cache servers) in an optimal way while reducing things like round tripping, with naive code? (e.g. it can automagically parallelize and optimize the &quot;N+1 Query Problem&quot; into an efficient query that minimizes duplicated requests and round trips, with no intervention, and the single &#x27;query&#x27; can operate over multiple data sources like mentioned previously.) In other words: it does side effects all the time, and makes them manageable in ways you could only dream of in other languages. Did I mention all of that was done in a library? :)<p>I mean, we definitely have a sales problem, don&#x27;t get me wrong. We could spit these stories better or clean up the presentation. I can list off a dozen things Haskell is poor at, or probably an infinite number given the time. But you sort of chose <i>literally the worst example in the world to make your point</i>.<p>I would suggest you actually spend some time with the language in anger. It is not easy. But I&#x27;ve been writing &#x27;real world&#x27; software in Haskell for years, and it&#x27;s no more difficult or &#x27;magical&#x27; than any other part of being a software developer. It&#x27;s just more rewarding because my code works far more often. And working code seems to be something that&#x27;s rare in the software world these days ;)