Then chaining base on condition

[zorture]

Is the below code possible? I am getting Error. Type '()' cannot conform to 'Thenable'; only struct/enum/class types can conform to protocols.
How do I achieve condition chaining inside then closure?

    firstly {
        Promise.value(1)
    }.then { _ in
        Promise.value(2)
    }.then { value in
        if value > 0 {
            Promise.value(3)
        } else {
            Promise.value(4)
        }
    }.done {
        print($0)  
    }

[GarthSnyder]

if in Swift is not an expression, so the last then returns nothing, aka Void, aka (). Just put explicit returns in for values 3 and 4.

[mxcl]

Probs need to specify return type too:

firstly {
    Promise.value(1)
}.then { _ in
    Promise.value(2)
}.then { value -> Promise<Int> in
    if value > 0 {
        return Promise.value(3)
    } else {
        return Promise.value(4)
    }
}.done {
    print($0)  
}