Example from http://davesquared.net/2014/04/fsharp-regex-provider.html

match.cs

public IEnumerable<string> GetSamples(string s) {
    var re = @"\{%\s*(?<tag>\w+)\s*\%\}(?<contents>(?s:.*?))\{%\s*end\1\s*%\}";
    return Regex.Matches(s, re)
                .Cast<Match>()
                .Where(m => m.Groups["tag"].Value == "sample")
                .Select(m => m.Groups["contents"].Value.Trim());
}

match.fs

let getSamples s : string seq =
    let re = @"\{%\s*(?<tag>\w+)\s*\%\}(?<contents>(?s:.*?))\{%\s*end\1\s*%\}"
    Regex.Matches(s, re)
        |> Seq.cast<Match>
        |> Seq.filter (fun m -> m.Groups.["tag"].Value = "sample")
        |> Seq.map (fun m -> m.Groups.["contents"].Value.Trim())