I'm interested in what the trade off between "lazy by default" and "Eager by default, with some great lazy data structures you can use" is? Often programming l

I'm interested in what the trade off between "lazy by default" and "Eager by default, with some great lazy data structures you can use" is? Often programming language support for streams will feel a little second class, and I'd love to have something as first class seeming as Haskells lazy list - but that's a minority of the time for me.