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Pattern matching and C# objects
f#c#

Hi all.

Is it possible to use F# pattern maching for C# created objects? Like in:

C#

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namespace Calc
{
    class Expr
    {
       class Sum {...}
       class Sub {...}
       class Mult {...}
       class Div {...}
       ...
    }
}

F#

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open Calc

let rec eval expr:Expr =
    match expr with
    | Sum x y -> (eval x) + (eval y)
    | Sub x y -> (eval x) - (eval y)
    | Mult x y -> (eval x) * (eval y)
    | Div x y -> (eval x) / (eval y)
    | ...

Any help will ber really appreciated.

Thanks in advance.

.

You can use :? operator to exactly test classes

and :> operator to test is given class parent of your class.

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open Calc

let rec eval (expr:Expr) =
    match expr with
    | :? Sum -> (eval expr.x) + (eval expr.y)

    //...
By on 11/8/2007 1:07 AM ()

Thanks for the answer. I really have overlooked the :? and :> operators.

By on 11/9/2007 6:42 AM ()

Active patterns may be an option, there's a good description of how they work here:
[link:www.infoq.com]

Cheers,
Rob

By on 11/8/2007 4:26 AM ()

Thanks for the tip on active patterns. They seem very interesting. The downside is that one have to redefine the data structures. Is there any workaround for that? I mean, any way to do not have to redefine the data structures?

By on 11/9/2007 6:45 AM ()

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