peg-1-printPeg-2.fs

let rec pegToString expr =
    let pegToStringParen = function
    | Terminal _ | NonTerminal _ | Epsilon as x -> pegToString x
    | x -> "(" + pegToString x + ")"

    match expr with
    | Terminal x -> "\"" + x + "\""
    | NonTerminal x -> x
    | Epsilon -> "<epsilon>"
    | Sequence x -> List.map pegToStringParen >> List.reduce (fun a b -> a + " " + b) <| x
    | Choice x -> List.map pegToStringParen >> List.reduce (fun a b -> a + " / " + b) <| x
    | ZeroOrMore x -> pegToStringParen x + "*"
    | OneOrMore x -> pegToStringParen x + "+"
    | Optional x -> pegToStringParen x + "?"
    | And x -> "&" + pegToStringParen x
    | Not x -> "!" + pegToStringParen x


let printPeg expr =
    printfn "%s" <| pegToString expr