peg-1-parse-pt3.fs

    | ZeroOrMore x ->
        let rec parseList off =
            seq {
                match parse off x with
                | (Unmatched, _) -> ()
                | (y, z) -> yield (y, z)
                            yield! parseList z
            }
        let s = List.ofSeq <| parseList offset
        if List.isEmpty s then (EmptyMatch, offset) 
        else (Production <| List.map fst s, snd <| List.maxBy snd s)
    | OneOrMore x ->
        let rec parseList off =
            seq {
                match parse off x with
                | (Unmatched, _) -> ()
                | (y, z) -> yield (y, z)
                            yield! parseList z
            }
        let s = List.ofSeq <| parseList offset
        if List.isEmpty s then (Unmatched, offset)
        else (Production <| List.map fst s, snd <| List.maxBy snd s)
    | Optional x ->
        match parse offset x with
        | (Unmatched, _) -> (EmptyMatch, offset)
        | y -> y
    | And x ->
        match parse offset x with
        | (Unmatched, _) -> (Unmatched, offset)
        | _ -> (EmptyMatch, offset)
    | Not x ->
        match parse offset x with
        | (Unmatched, _) -> (EmptyMatch, offset)
        | _ -> (Unmatched, offset)

    parse 0 grammar.[start]