Whereas I believe that concepts are tools for programmers to reach for when appropriate, functional programmers believe concepts are rules and reaching for them should be mandatory, no matter how much bullshit they force you to add for no reason other than you accepted from the get go that, for example, immutability should be mandatory.
This is a massive fundamental problem with Haskell and all language that take hardline stances on things that are better left to the users. In this regard, I’d say it’s a complete failure. It’s horrible for teaching. You need to know more than you need to know for Java just to use it. It’s horrible for research. It has hardline fundamental stances that rejects exploration, and therefor is research averse. It is horrible for industrial applications as there are massive ranges of industry that simply cannot give to the whims of Haskell for one reason or another, but probably multiple reasons cause Haskell is terrible.