[ImprobableTruth]

Sure, it's best to work with rather than against the language, but for most languages support of functional programming is not binary, just like with OOP.

I'm pretty sure most of the complaints are generally of the "This FP thing would work well here, but the language is unfortunately not quite there" nature rather than "I will try to implement profunctor optics in C no matter the cost" square peg in round hole crazyness.

>when you force lots of maps & filters in a language that can't do fusion and function calls are kind of expensive

I think that's perfect example to show that it's really about degrees, because fusion is really a Haskell thing. Sure, it's a nice-to-have, but it's definitely not essential to functional programming.

And when people want sum types (which aren't even really FP, ALGOL had them first!), it's often because the idiomatic alternative just kind of sucks for what they're doing. Trying to "implement" sum types in a language without support is nonsensical, but complaints about lacking them are pretty understandable I think.