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.
Extension of something written in a language like Haskell[0] definitely poses challenges. Even if the language makes it un-modifiable in your environment, there's no reason it can't be treated like a black-box component and used.
[0] By "like Haskell", I really mean "unreadable/unwritable by the team supporting it". This could apply equally to Ruby, Java, bash, SQL, JavaScript, and Python depending on the makeup of the team supporting it.
> "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.