So, the thing that always gets Haskell folks when dealing with an implementation (2) is that you can't get uniform data representation when dealing with things

So, the thing that always gets Haskell folks when dealing with an implementation (2) is that you can't get uniform data representation when dealing with things like arrays. It means you have to unbox things. Arguably, the situation is not much better in malloc land; if you malloc a large multiple of your object size, you're explicitly saying, "I want this to be unboxed", but by this point you've wandered into generics land. (3) is annoying. Who likes 31-bit integers? Not I!