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Event in F# classes
f#classes

Hi all,

I am looking for a simple way to take an event filter and expose it on a classes interface. I came up with the code below, which looks good to me but won't compile because trigger is out of scope. Would it be posssible to alter the compile so it is in scope, as it looks like it should be to me, or is there a specific reason for it being out of scope?

-----------8<----------------------8<----------------------8<----------------------8<-----------

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#light
open System.Windows.Forms

type LeftClickForm = class
    inherit Form
    val LeftMouseClick : Idioms.IEvent<MouseEventArgs>
    new() as x =
        let trigger, event = IEvent.create()
        {LeftMouseClick = event}
        then
            x.MouseClick
            |> IEvent.filter (fun e -> e.Button = MouseButtons.Left) 
            |> IEvent.listen (fun e -> trigger e)
end

-----------8<----------------------8<----------------------8<----------------------8<-----------

If compiled you get the following error:
C:\prog.fs(13,39): error: FS0039: The value or constructor 'trigger' is not defined.

.

The parser binds "then expr" over the whole preceeding expr (let-expr), rather than the immediately preceeding object expression. I've logged the bug. Thanks.

By on 9/27/2006 4:13 AM ()

Yes, this is currently a bit of a pain - trigger is not in scope ("let" binds more tightly than "then", and the syntactic forms permitted for constructors are very limited due to .NET rules) .

You might prefer to have a hidden constructor and a static "Create" method, which is in general more flexible.

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type LeftClickForm = class
    inherit Form
    val LeftMouseClick : Idioms.IEvent<MouseEventArgs>
    new(leftMouseClickEvent) = {LeftMouseClick = leftMouseClickEvent}
    static member Create() =
        let trigger, event = IEvent.create()
        let x = new LeftClickForm(event) 
        x.MouseClick
          |> IEvent.filter (fun e -> e.Button = MouseButtons.Left) 
          |> IEvent.listen (fun e -> trigger e);
        x
        
end

Notes:

Don

By on 9/27/2006 4:12 AM ()

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