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How to work around lack of parameter overloading
f#

Hi,

I want to define the - operator between scalars and vectors, but I want it work for both vector - scalar and for scalar - vector. Is there any way to do that in F#? I was hoping that if I defined these functions inline it would work, but no :(

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[<AutoOpen>]
module VectorOperators = 

    let inline (-) (scalar: float) (vector: #Vector<float>) = 
        DenseVector.init vector.Count (fun i -> scalar - vector.[i])

    let inline (-) (vector: #Vector<float>) (scalar: float) = 
        DenseVector.init vector.Count (fun i -> vector.[i] - scalar)
.

You can extend a binary operator using the ternary operator (?<-) and an intermediate type.

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type VectorOperators = VectorOperators with 
    static member (?<-) (scalar: float,VectorOperators,vector: #Vector<float>) =
        DenseVector.init vector.Count (fun i -> scalar - vector.[i])
 
    static member (?<-) (vector: #Vector<float>,VectorOperators,scalar: float) =
        DenseVector.init vector.Count (fun i -> vector.[i] - scalar)

    static member inline (?<-) (a,VectorOperators,b) = a - b

let inline (-) a b = a ? (VectorOperators) <- b

I didn't test it. But it should work.

By on 12/6/2011 3:34 PM ()

Great idea!

By on 12/7/2011 1:33 AM ()

Just an unrelated note: you can easily search the FPish archives for the term "overloading".

By on 11/26/2011 2:13 PM ()

Well, generally you should define operators as static members on the class (in this case, Vector<_>). This would solve all problems.

By on 11/19/2011 8:35 AM ()

The problem is that I'm trying to extend the Math.NET classes which are defined in C# with some more operators, and not defining my own classes. I can't use type extensions either, because they don't support operators (which is unexpected as they do support static members)

By on 11/19/2011 9:08 AM ()

Well, then I'd recommend defining two different operators (for example >- and -<). I see no other type-safe way.

By on 11/19/2011 10:50 AM ()

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