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Option.ofNull
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In F#, one can write the Option.ofNull combinator in the following way:

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let ofNull = function
    | null -> None
    | x -> Some x

Annotating with JavaScriptAttribute allows it to work on the client side. It works for most scenario on the client side, but I've had trouble in relation with JavaScript's semantics for null and undefined.

The following seemed to work better:

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module Option =
    let ofNull x =
    if x ==. JavaScript.Undefined then None
    else Some x

I'm not too sure if it's the best way to go about it and/or if there would be a way that the same combinator could be used for both client and server side.

Thanks!

David

.

On the server side, ==. always returns Unchecked.defaultof<bool>, ie. false. In JavaScript, as you noted, x == undefined returns true iff x === null || x === undefined. So I think the best way to implement ofNull for both client and server-side is probably to combine both your solutions:

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module Option =
    let ofNull = function
        | null -> None
        | x -> if x ==. JavaScript.Undefined then None else Some x

I will investigate however why the simple null -> None | x -> Some x doesn't function as expected, it looks like the semantics might need some clarification.

By on 11/19/2014 2:19 AM ()

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