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Microsoft.FSharp.Collections.Seq and System.Data.DataView
f#

My understanding is that the Microsoft.FSharp.Collections.Seq module is supposed to work with any type that implements an IEnumerable interface, and that a System.Data.DataView object has an IEnumerable interface. However, I'm getting errors.

I have a System.Data.DataView called programView. When I enter

let length = Seq.length programView;;

in FSI, it says error, type System.Data.DataView is not compatible with the type seq<'a>. And when I enter

let prgList = Seq.toList programView;;

it says toList is not defined. I'm new to both F# and .NET, and expect there's probably something elementary at work here. I did not get an error on opening Microsoft.FSharp.Collections, so I'm assuming it should actually be open, but the nonrecognition of Seq.toList does suggest some problem with the library.

Any illumination would be greatly appreciated.

.

If DataView is only IEnumerable, and not IEnumerable<T>, then this would explain it. You can use "Seq.cast<T>" to convert to the <i>generic<i> IEnumerable type, and then be able to use the other Seq functions. The "toList" not being defined sounds fishy; Seq.toList should already be in scope, even without opening any namespaces. I'm not too familiar with DataView, but below is an example from the Regex library with the same issue; m.Groups is an IEnumerable, but not an IEnumerable<Group>, so I have to Seq.cast it. open System.Text.RegularExpressions let m = Regex.Match("abc", "(.).(.)") m.Groups |> Seq.cast<Group> |> Seq.iter (fun x -> printfn "group: %s" x.Value)

By on 4/7/2010 5:29 PM ()

What version of F# are you using?
In older versions, Seq.toList used to be Seq.to_list.

By on 4/8/2010 1:27 AM ()

I'm currently using F# 1.9.6.16.

By on 4/8/2010 2:42 PM ()

There you go. Using Seq.to_list + Brian's suggestion should do.

(Upgrade to a newer F# release maybe :-) )

By on 4/9/2010 4:51 AM ()

Thanks!

By on 4/9/2010 4:01 PM ()

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