BF interpreter for the Trill iOS App

bf.tr

foreign type String {
  foreign init(_: *Int8) -> String
  foreign var length: Int
  foreign func charCodeAt(_: Int) -> Int8
  foreign static func fromCharCode(_: Int8) -> String
}

type Op {
  let opcode: Int8
  var operand: Int
}

foreign type Array {
  foreign init(_: Int) -> Array
  foreign subscript(_: Int) -> Any
  foreign func fill(_: Any)
  foreign func push(_: Any)
  foreign func pop() -> Any
  foreign var length: Int
}

func toBF(_ prog: *Int8) -> Array {
  var str = String(prog)
  var ops = Array(0)
  var pcStack = Array(0)
  for var i = 0; i < str.length; i += 1 {
    let opcode = str.charCodeAt(i)
    var op = Op(opcode: opcode, 
                operand: 0)
    if opcode == '[' {
      pcStack.push(i)
    } else if opcode == ']' {
      op.operand = pcStack.pop() as Int
      var old = ops[op.operand] as Op
      old.operand = i
      ops[op.operand] = old
    }
    ops.push(op)
  }
  return ops
}

func runBF(_ ops: Array) {
  var memory = Array(30000)
  memory.fill(0)
  var opcodeStack = Array(0)
  var p = 0
  var pc = 0
  while pc < ops.length {
    let op = ops[pc] as Op
    switch op.opcode {
      case '+':
        memory[p] += 1
      case '-':
        memory[p] -= 1
      case '<':
        p -= 1
      case '>':
        p += 1
      case '.':
        let s = String.fromCharCode(memory[p] as Int8)
        print(s)
      case '[':
        if memory[p] == 0 {
          pc = op.operand
          continue
        }
      case ']':
        if memory[p] != 0 {
          pc = op.operand
          continue
        }
    }
    pc += 1
  }
}

func main() {
  runBF(toBF("++++++++++[>+++++++>++++++++++>+++>+<<<<-]>++.>+.+++++++..+++.>++.<<+++++++++++++++.>.+++.------.--------.>+.>."))
}