open System
open System.Text.RegularExpressions

let main() =
    // This tests whether a pattern matches a string.
    let match1 = Regex.IsMatch("peach", "p([a-z]+)ch")
    printfn "%b" match1

    // For other regexp tasks, you'll need to create a Regex object.
    let r = Regex("p([a-z]+)ch")

    // Many methods are available on these objects. Here's a match test like we saw earlier.
    printfn "%b" (r.IsMatch("peach"))

    // This finds the match for the regexp.
    printfn "%s" (r.Match("peach punch").Value)

    // This also finds the first match but returns the start and end indexes for the match.
    let m = r.Match("peach punch")
    printfn "idx: [%d %d]" m.Index (m.Index + m.Length)

    // The Groups property provides information about both the whole-pattern matches 
    // and the submatches within those matches.
    let groups = r.Match("peach punch").Groups
    printfn "%A" [for g in groups -> g.Value]

    // Similarly, we can get information about the indexes of matches and submatches.
    printfn "%A" [for g in groups -> [g.Index; g.Index + g.Length]]

    // The Matches method finds all matches in the input.
    let matches = r.Matches("peach punch pinch")
    printfn "%A" [for m in matches -> m.Value]

    // We can limit the number of matches.
    let limitedMatches = r.Matches("peach punch pinch") |> Seq.take 2
    printfn "%A" [for m in limitedMatches -> m.Value]

    // Our examples above had string arguments. We can also provide byte arrays.
    let bytes = Text.Encoding.ASCII.GetBytes("peach")
    printfn "%b" (r.IsMatch(Text.Encoding.ASCII.GetString(bytes)))

    // The regexp package can also be used to replace subsets of strings with other values.
    printfn "%s" (r.Replace("a peach", "<fruit>"))

    // The Replace method allows you to transform matched text with a given function.
    let upperReplace (m: Match) = m.Value.ToUpper()
    let result = r.Replace("a peach", MatchEvaluator(upperReplace))
    printfn "%s" result

main()