Lazy<'T> vs anonymous functions

Question

Is there any advantage to using the .NET lazy operator instead of a plain function?

For example:

let x = lazy ...
let y = lazy (1 + x.Value)

let x = (fun () -> ...)
let y = (fun () -> 1 + x())

Answer 1

The difference between a lazy value and a function is that a lazy value is evaluated only once. It then caches the result and accessing it again will not recalculate the value. A function is evaluated each time you call it.

This has performance implications and it also matters when you have side effects. For example, the following prints "calculating x" just once:

let x = lazy (printfn "calculating x"; 1)
let y = lazy (1 + x.Value)
y.Value + y.Value

The following prints "calculating x" two times:

let x = (fun () -> printfn "calculating x"; 1)
let y = (fun () -> 1 + x())
y () + y ()