Nothing. I honestly have no idea what they're talking about. Haskell apps tend to be tanks once they're deployed. The only issue I've ever seen was a Haskell app getting OOMed because the dev box only had 8GB of RAM and someone deployed some data science infra to the box sometime later (which needed >8GB RAM). I think this statement is more accurate:

> "Problem: There is the PostgREST written in Haskell, not in Go"

Moreover, if you want to use something like PostgREST but need to extend it, and don't know Haskell, this is a completely legitimate problem. While I'm all for competing implementations, the pREST author's claim for why it's needed is inaccurate.