mal/impls/fsharp/step2_eval.fs

module REPL
    open System
    open Node
    open Types

    let rec eval env ast =
        (* Printer.pr_str [ast] |> printfn "EVAL: %s" *)
        match ast with
        | Symbol(sym) -> match Env.get env sym with
                         | Some(value) -> value
                         | None -> Error.symbolNotFound sym |> raise
        | Vector(_, seg) -> seg |> Seq.map (eval env) |> Array.ofSeq |> Node.ofArray
        | Map(_, map) -> map |> Map.map (fun k v -> eval env v) |> makeMap
        | List(_, (a0 :: rest)) ->
            match eval env a0 with
            | BuiltInFunc(_, _, f) -> List.map (eval env) rest |> f
            | _ -> raise <| Error.errExpectedX "func"
        | _ -> ast

    let READ input =
        Reader.read_str input

    let EVAL env ast =
        Some(eval env ast)

    let PRINT v =
        v
        |> Seq.singleton
        |> Printer.pr_str
        |> printfn "%s"

    let REP env input =
        READ input
        |> Seq.ofList
        |> Seq.choose (fun form -> EVAL env form)
        |> Seq.iter (fun value -> PRINT value)

    let getReadlineMode args =
        if args |> Array.exists (fun e -> e = "--raw") then
            Readline.Mode.Raw
        else
            Readline.Mode.Terminal

    [<EntryPoint>]
    let main args =
        let mode = getReadlineMode args
        let env = Env.makeRootEnv ()
        let rec loop () =
            match Readline.read "user> " mode with
            | null -> 0
            | input ->
                try
                    REP env input
                with
                | Error.EvalError(str)
                | Error.ReaderError(str) ->
                    printfn "Error: %s" str
                | ex ->
                    printfn "Error: %s" (ex.Message)
                loop ()
        loop ()