What does this '()' notation mean?

Question

I just started to learn F#. The book uses the following notation:

let name() = 3
name()

what that differs from this:

let na         


        

Answer 1

Using () creates a function which takes a paramter of type unit, rather than the second case which is just a simple integer.

This is particularly important when you want to control execution of the function.

The main difference is when you have

let name() = 
    printfn "hello"
    1

vs

let name = 
    printfn "hello"
    1

then

let t = name + name

will print "hello" once. But

let t = (name()) + (name())

will print "hello" twice.

You have to be careful with this when considering the order in which functions are evaluated.

Consider the following program:

let intversion = 
    printfn "creating integer constant"
    1

printfn "integer created"

let funcversion() =
    printfn "executing function"
    1

printfn "function created"

let a = intversion + intversion
printfn "integer calculation done"
let b = (funcversion()) + (funcveriosn())
printfn "function calculation done"

This will print the following in order

1. creating integer constant
2. integer created
3. function created
4. integer calculation done
5. executing function
6. executing function
7. function calculation done