let RCBF (pgmStr : string) = let pgm = Seq.toArray pgmStr // Turn program into an array let ptr = ref 0 // Pointer into input let ip = ref 0 // Instruction Pointer let input = ref (Array.create 100 0)

let InputNumber() =
    let mutable fValid = false
    let mutable num = 0
    printfn "Enter a valid number"
    fValid <- Int32.TryParse(Console.ReadLine(), &num);
    while not fValid do
        printfn "Invalid input.  Please enter a valid number"
        fValid <- Int32.TryParse(Console.ReadLine(), &num);
    num

let InputAscii() =
    printfn "Enter an ascii character"
    let chOut = (Console.ReadKey().KeyChar)
    printfn ""
    int chOut

let AdvanceIp() = ip := !ip + 1                                     // Advance IP
let RetreatIp() = ip := !ip - 1                                     // Decrement IP

let SkipBrackets fForward =
    if (!input).[!ptr] <> 0 then                                       // If we have a 0 input
        AdvanceIp()                                                 // Then just advance to next instruction
    else                                                            // otherwise
        let fnMove = if fForward then AdvanceIp else RetreatIp      // get the appropriate function to move forward or backward
        let mutable cBrackets = 1                                   // Count of brackets we've seen
        while cBrackets > 0 do                                      // While we have unmatched brackets
            fnMove()                                                // move to the next character
            if !ip >= 0 && !ip < pgm.Length then                    // and if we're still within range
                match pgm.[!ip] with                                // look at the character
                | '[' -> cBrackets <- cBrackets + 1                 // If it's a '[' then count up brackets
                | ']' -> cBrackets <- cBrackets - 1                 // If it's a ']' then count down brackets
                | _ -> ignore(0)                                    // Ignore anything else
        AdvanceIp()                                                 // When we're on the matching bracket, skip to the next instruction

let MovePtr fRight =
    if fRight then
        ptr := !ptr + 1
        if !ptr >= (!input).Length then
            Array.Resize(input, (!input).Length + 20)
    else
        ptr := !ptr - 1
        if !ptr < 0 then
            let newInput = Array.create ((!input).Length + 20) 0
            Array.ConstrainedCopy(!input, 0, newInput, 20, (!input).Length)
            ptr := 19

let interpretCmd() =
    match pgm.[!ip] with
    | '>' -> MovePtr true; AdvanceIp()
    | '<' -> MovePtr false; AdvanceIp()
    | '+' -> (!input).[!ptr] <- (!input).[!ptr] + 1; AdvanceIp()
    | '-' -> (!input).[!ptr] <- (!input).[!ptr] - 1; AdvanceIp()
    | '.' -> printf "%c" (char (!input).[!ptr]); AdvanceIp()
    | ',' -> (!input).[!ptr] <- InputNumber(); AdvanceIp()
    | '~' -> (!input).[!ptr] <- InputAscii(); AdvanceIp()
    | '[' -> SkipBrackets true
    | ']' -> SkipBrackets false
    | _ -> AdvanceIp()

while !ip >= 0 && !ip < pgm.Length do
    interpretCmd()

</div>

Hello world in RCBF (stolen from the Wiki site):
<div style='width: full; overflow: scroll'>
```fsharp
let pgmHelloWorld = "++++++++++[>+++++++>++++++++++>+++>+<<<<-]>++.>+.+++++++..+++.>++.<<+++++++++++++++.>.+++.------.--------.>+.>."
let tape = Array.create 5 0
Rcbf pgmHelloWorld tape