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VB to F# interfacing with Sequences
f#accumulatorseqvb

I'm playing around with F# in my spare time (yeah, right) and attempting to move data between VB.Net and F#. It is working out pretty well, however I'm not always sure how to cast or manipulate the results. Here is a small example:

MyVB.VB

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        Dim VBarray(10) As Double
        For idx = 0 To VBarray.Count - 1
            VBarray(idx) = idx
        Next

        Dim objFS As New FCSDataLibrary.FCSData.MyFSClass(VBarray)

        For idx = 0 To VBarray.Count - 1
            VBarray(idx) = idx * 10
        Next

        objFS.AppendSeed(VBarray)

        Dim info = objFS.LAccum

My FSharp.fs

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    type MyFSClass(seeds:seq<float>) = class

      let mutable laccum = seq<float>
      let mutable accseeds = seeds

      member x.Seeds = seeds
      member x.LAccum = laccum
      member x.AccSeeds = accseeds
 
      member x.AppendSeed(value: seq<float>) = laccum <- Seq.append value

The structure of my info variable comes back as:

info {FCSDataLibrary.FCSData.AppendSeed@108-1}

Microsoft.FSharp.Core.FSharpFunc(Of System.Collections.Generic.IEnumerable(Of Double), System.Collections.Generic.IEnumerable(Of Double))

However, I'm not sure how to work with the FSharp Func results in VB.Net? It appears to return a function and not a sequence of sequences.

dgp

.

Seq.append expects two values, and you're only giving it one. That means you've partially-applied that function, which results in a new function that expects the missing parameter, and will return the end result when called.

Try 

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Seq.append laccum value

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More broadly, Seq.append isn't particularly efficient. If you end up calling AppendSeed many times, I would choose a different data structure than a sequence for internal storage. ResizeArray might be appropriate.

By on 1/30/2013 8:26 AM ()

Thanks Joel. That makes sense.

I'm toying around with structure to see how they cast between VB and F#. So, it guess the value it returned was the internal name of the lambda expression -- @108-1.

A sequence of sequences is probably not what I want to use in the long run, more of a matrix. I will be targeting an m (row) x n (col) array and computing the euclidean distances along the rows. Then comparing the results to find the shortest distance.

dgp

By on 1/30/2013 9:03 AM ()

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