I think lazy evaluation is very hard, especially when you are dealing with a codebase of of say 50 files with structures containing other structures, the line between lazy and strict is very hard to see.

The difficulty learning lazy evaluation skill goes from

* 0 where you know nothing to 5 where you sort of understand.

* 5 - 90 is a space where you think you know what it is, but you really don't. You'll probably get yourself in trouble more than helping.

* 90-100 is when you grok it and can use it effectively.

I am an avid haskell user for a few years and I am still 50/50 on most of my conclusions about laziness without asking someone else.

    > let x = [1 .. 100] :: [Int]
    > seq x () -- force the first cons
    > :sprint x
    x = 1 : _ -- we evaluated the first cons
    > foldr (\e l -> e + l) 0 x
    5050 -- printing this value forces foldr to complete
    > :sprint x
    x = [1,2,3,4,5...100] -- all conses evaluated