tomo/docs/optionals.md

Optional Values

A very common use case is values that may or may not be present. You could represent this case using enums like so:

enum MaybeInt(AnInt(x:Int), NoInt)

func maybe_takes_int(maybe_x:MaybeInt):
    when maybe_x is AnInt(x):
        say("Got an int: $x")
    else:
        say("Got nothing")

However, it's overly onerous to have to define a separate type for each situation where you might want to not have a value. Instead, Tomo has built-in support for optional types:

func maybe_takes_int(x:Int?):
    if x:
        say("Got an int: $x")
    else:
        say("Got nothing")

This establishes a common language for talking about optional values without having to use a more generalized form of enum which may have different naming conventions and which would generate a lot of unnecessary code.