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Type annotation for empty list
f#

Hello guys,

I would like to know if is possible to force the type of a empty list ("[]"), which is by default 'a list.

I would like to do this becouse my function computeMoves should return a empty list if there is no moves from that node. I think it must be a Position list beause the if then type must match with the else part, is that right?

Thanks in advance,

Pedro Dusso

.

Hey Pedro,
normally you don't have to annotate the type explicitly, since the compiler will infer the type of the empty list from the other branch of the if:

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let f () =
    if true then [1]
    else []

However, if you do need it, you can do this:

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let (k : int list) = []

or

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let f () =
    if true then [1]
    else ([] : int list)
By on 6/17/2010 12:04 PM ()

Thanks mau it really worked. However, I was also ending the if then else with a elif, than the compiler was expecting a unit... :P my mistake.

Let me keep working!

(*Just for testing...*)

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lif(position.ContainsKey(4)) then

            ([] : Position list)

        else ([] : Position list)
By on 6/17/2010 12:15 PM ()

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