Is there something about purely functional languages that make them attractive to blockchain applications? I remember a post on here a little while ago complaining about Haskell adoption in industry was being mostly led by cryptocurrencies.
Another might say it was a weakness for snake oil.
To give you an example of how you would use some crypto-related library that implemented its API (?) in OOP:
let x = new Foo.bar in
x#absorb a;
x#squeeze b;
x#reset
This (this entire file) is a great example, too!