Why is lazy evaluation useful?

Question

I have long been wondering why lazy evaluation is useful. I have yet to have anyone explain to me in a way that makes sense; mostly it ends up boiling down to \"trust me\".<

Answer 1

I don't know how you currently think of things, but I find it useful to think of lazy evaluation as a library issue rather than a language feature.

I mean that in strict languages, I can implement lazy evaluation by building a few data structures, and in lazy languages (at least Haskell), I can ask for strictness when I want it. Therefore, the language choice doesn't really make your programs lazy or non-lazy, but simply affects which you get by default.

Once you think of it like that, then think of all the places where you write a data structure that you can later use to generate data (without looking at it too much before then), and you'll see a lot of uses for lazy evaluation.