Why do F# functions evaluate before they are called?

Question

If I define a module as such:

module Module1
open System

let foo =
    Console.WriteLine(\"bar\")

Then, in interactive do

Answer 1

I believe let foo = x is essentially a static value that gets evaluated immediately, once. If you want a parameterless function, you would need let foo () = Console.WriteLine("bar"), using it as foo ().

If you don't want to have to use the parentheses when calling, something like type Test () = static member foo with get () = System.Console.WriteLine("bar"), using it as Test.foo should work.

Answer 2

Function bodies are evaluated when the function is called, just as you want. Your problem is that foo is not a function, it's a variable.

To make foo a function, you need to give it parameters. Since there are no meaningful parameters to give it, the unit value (()) would be the conventional parameter:

let foo () =
    Console.WriteLine("bar")

Accordingly a call of this function would look like foo ().