F#: How do I use Map with a Collection (like Regex Matches)?

Question

Soo... F# no longer has IEnumerable.map_with_type... which is the way people were mapping over collections. How do I do that now?

let urlPat = "href\\s*=\\s*(?:(?:\\\"(?<url>[^\\\"]*)\\\")|(?<url>[^\\s]* ))";;
let urlRegex = new Regex(urlPat)
let matches = 
    urlRegex.Matches(http("http://www.google.com"))

let matchToUrl (urlMatch : Match) = urlMatch.Value
let urls = List.map matchToUrl matches

Thanks!

Answer 1

Is Seq.cast what you are looking for?

Answer 2

Hi, you would write the last line like this:

let urls = Seq.map matchToUrl (Seq.cast matches);;

And this can be written in a nicer way using pipelining operator:

let urls = matches|> Seq.cast |> Seq.map matchToUrl;;

F# automatically figures out what is the right target type (because it knows what matchToUrl looks like). This is available only for Seq, so you can use List.of_seq to get the data into a list again.