How to return a module from expressions in f #

Question

How can I return unit from an expression in f #? For instance:

 let readInt = let str = Console.ReadLine() let (succ, num) = Int32.TryParse(str) match succ with | true -> Some(num) | _ -> None match readInt with | Some(v) -> Console.WriteLine(v) | None -> ignore //i don't want to do anything, // but i don't know how to ignore this brunch of the expression 

Answer 1

The value (only possible) of a unit in F # is written as

 () 

So your code will become

 ... | None -> () 

Answer 2

Just write () as follows

 match readInt with | Some(v) -> Console.WriteLine(v) | None -> () 

Answer 3

Remember the unit of measure () , it is convenient in many situations.

In this case, you can use the iter function from the Optional module :

 Option.iter Console.WriteLine readInt 

It also emphasizes the fact that iter functions (for example, those from the Seq , List and Array modules) will always give you a unit () value.