I'm trying to apply Seq functions on an IEnumerable. More specifically, it's System.Windows.Forms.HtmlElementCollection which implements ICollection and IEnumerable.
Since an F# seq is an IEnumerable, I thought I could write
let foo = myHtmlElementCollection |> Seq.find (fun i -> i.Name = "foo")
but the compiler will have none of it, and complains that "The type 'HtmlElementCollection' is not compatible with the type 'seq<'a>'".
However, the compiler willingly accepts the IEnumerable in a for .. in .. sequence expression:
let foo = seq { for i in myHtmlElementCollection -> i } |> Seq.find (fun i -> i.Name = "foo")
What do I need to do in order for the IEnumerable to be treated just like any old F# seq?
NB: This question is marked as a duplicate, but it's not. The linked "duplicate" is about untyped sequences (a seq from the seq { for ... } expression), whereas my question is about typed sequences.
La solution
F#'s type seq<'a> is equivalent to the genericIEnumerable<'a> in System.Collections.Generic, but not to the non-genericIEnumerable. You can use the Seq.cast<'a> function to convert from the non-generic one to the generic one:
let foo = myHtmlElementCollection
|> Seq.cast<HtmlElement>
|> Seq.find (fun i -> i.Name = "foo")