open CS334

let rec repl() =
    printf "Enter an expression (type 'quit' to quit): "
    let input = System.Console.ReadLine()
    if input = "quit" then
        printfn "Goodbye!"
        exit 0
    else
        // parsing can fail, so we made it return an 'Expr option' type
        // pattern match to get Some AST or None AST.
        let ast_maybe = parse input
        match ast_maybe with
        | Some ast -> printfn "%A" ast
        | None -> () // do nothing (returns unit)
    repl()

[<EntryPoint>]
let main args =
    repl()
    0