Meh

brainfuck.swag

read("", :program, {
  def(:program_length, send(program, :length))
  def(:program_location, 0)
  
  def(:input, (1, 2, 3, 4))
  def(:input_location, 0)

  def(:program_char, {
    send(program, :substring, program_location, +(program_location, 1))
  })
  def(:get_input, {
    def(:input_location, +(input_location, 1))
    send(input, :get, -(input_location, 1))
  })
  def(:pointer, 0)

  def(:method_missing, :missing_name, { 0 })

  def(:inc_pointer, :amount, {
    def(:pointer, +(pointer, amount))
  })

  def(:current, { def(+(:stack_, pointer)) })

  def(:incr, :amount, {
    def(+(:stack_, pointer), +(current, amount))
  })

  def(:set, :amount, {
    def(+(:stack_, pointer), amount)
  })

  def(:output, ())

  while(<(program_location, program_length), {
    def(:char, program_char())

    if(=(char, ">"), { inc_pointer(1) })
    if(=(char, "<"), { inc_pointer(-1) })
    if(=(char, "+"), { incr(1) })
    if(=(char, "-"), { incr(-1) })
    if(=(char, "."), { send(output, :add, current) })
    if(=(char, ","), { set(get_input()) })
    if(=(char, "["), {
      if(=(current, 0), {
        def(:program_location, +(program_location, 1))
        def(:br_count, 1)
        while(>(br_count, 0), {
          def(:char, program_char())
          if(=(char, "["), { def(:br_count, +(br_count, 1)) })
          if(=(char, "]"), { def(:br_count, -(br_count, 1)) })
          def(:program_location, +(program_location, 1))
        })
      })
    })
    if(=(char, "]"), {
      if(=(current, 0), {}, {
        def(:br_count, 1)
        def(:program_location, -(program_location, 1))
        while(>(br_count, 0), {
          def(:char, program_char())
          if(=(char, "["), { def(:br_count, -(br_count, 1)) })
          if(=(char, "]"), { def(:br_count, +(br_count, 1)) })
          def(:program_location, -(program_location, 1))
        })
      })
    })
  
    def(:program_location, +(program_location, 1))
  })

  def(:string, "")
  repeat(send(output, :size), :index, {
    def(:string, +(string, send(str(send(output, :get, index)), :get, 0)))
  })
  print(string)
})

Will why would you make this

Entirely Logan's fault.