bf.fs

open System

type State = {
    Tape : int[]
    Index : int
}

let print_tape state : State =
    printfn "%A" state.Tape
    state

let shift_stmt v state: State =
    { state with Index = (state.Index + v) }

let increment_stmt v state : State =
    let new_value = (Array.get state.Tape state.Index) + v
    Array.set state.Tape state.Index new_value
    state

let while_stmt state : State =
    state

let stop_rec_stmt state : State =
    state

let print_stmt state: State =
    printf "%c" (char (Array.get state.Tape state.Index))
    state

let read_stmt state : State =
    let c = (Console.Readline())
    state
    
let cond code : State =
    let explode (s:string) =
        [for c in s -> c]
    code
    |> explode
    |> List.fold
        (fun acc c ->
            match c with
            | '>'  -> shift_stmt 1 acc
            | '<'  -> shift_stmt -1 acc
            | '+'  -> increment_stmt 1 acc
            | '-'  -> increment_stmt -1 acc
            | '['  -> while_stmt acc
            | ']'  -> stop_rec_stmt acc
            | '.'  -> print_stmt acc
            | ','  -> read_stmt acc
            | '#'  -> print_tape acc
            |  _   -> acc
        ) { Tape = Array.create 100 0; Index = 0 }

[<EntryPoint>]
let main argv =
    match argv with
    | [| first |] -> ignore (cond first) 
    | _           -> failwith "Must have only one arg"
    0