Brainf**k interpreter in Ruby

Question

I wrote this interpreter for a code challenge. Can this be written any cleaner/smaller? Could I reduce the amount of nested conditional/loops?

def brain_luck(code, input)
 output = ''
 cp = 0 # code pointer
 dp = 0 # data pointer
 ip = 0 # input pointer
 data = Array.new(10, 0)
 while cp < code.length
 case code[cp]
 when '>'
 dp += 1
 if dp == data.length
 data.push(0)
 end
 when '<'
 dp -= 1
 if dp == -1
 dp = 0
 data.unshift(0)
 end
 when '+'
 data[dp] = (data[dp].ord+1)%256
 when '-'
 data[dp] = (data[dp].ord-1)%256
 when '.'
 output += data[dp].chr
 when ','
 data[dp] = input[ip].ord
 ip += 1
 when '['
 if data[dp] == 0
 nest_count = 1
 while nest_count > 0
 case code[cp += 1]
 when '[' then nest_count += 1
 when ']' then nest_count -= 1
 end
 end
 end
 when ']' 
 if data[dp] != 0
 nest_count = 1
 while nest_count > 0
 case code[cp -= 1]
 when ']' then nest_count += 1
 when '[' then nest_count -= 1
 end
 end
 end
 end
 cp += 1
 end
 output
end

• Dair: I know you don't want to swear, but brain_luck is not the way to go. It's confusing since it doesn't make sense why there is a function like that. You could just do something like eval_program.
• Mirror318: brain_luck was how the code challenge presented it (same with the double * in brainf**k)
• Dair: Ok, if you need to submit it that way for the challenge, but outside of the challenge, I would highly recommend changing it. :)
• Simon Forsberg: Does it work for this BF-program now? ,>+>>>>++++++++++++++++++++++++++++++++++++++++++++>++++++++++++++++++++++++++++++++<<<<<<[>[>>>>>>+>+<<<<<<<-]>>>>>>>[<<<<<<<+>>>>>>>-]<[>++++++++++[-<-[>>+>+<<<-]>>>[<<<+>>>-]+<[>[-]<[-]]>[<<[>>>+<<<-]>>[-]]<<]>>>[>>+>+<<<-]>>>[<<<+>>>-]+<[>[-]<[-]]>[<<+>>[-]]<<<<<<<]>>>>>[++++++++++++++++++++++++++++++++++++++++++++++++.[-]]++++++++++<[->-<]>++++++++++++++++++++++++++++++++++++++++++++++++.[-]<<<<<<<<<<<<[>>>+>+<<<<-]>>>>[<<<<+>>>>-]<-[>>.>.<<<[-]]<<[>>+>+<<<-]>>>[<<<+>>>-]<<[<+>-]>[<+>-]<<<-]
• Mirror318: @SimonForsberg sure does ;)

Answer 1

Sure it can!

Steps I see to make it clean:

1. Create a class, define state attrs:

   private
   attr_reader :output, :code_pointer, :data_pointer, :input_pointer
   

2. define initialize method

   def initialize(args = {})
    @code = args[:code]
    @input = args[:input]
    @output = ''
    @code_pointer, @data_pointer, @input_pointer = 0, 0, 0
   end
   

3. define whens as a methods and give it right names: next_cell, prev_cell, increment, decrement, write_byte, read_byte and so on

4. define constant for configuration:

   OPERATORS = {
    '>' => :next_cell,
    '<' => :prev_cell,
    '+' => :increment,
    ...
   }
   

5. define method to evaluate code:

   def evaluate_code
    code.each { |operator| public_send OPERATORS[operator] }
   end
   

6. Finally instantiate object of your class and call evaluate_code

   BrainLuck.new(code: code, input: input).evaluate_code
   

I think you'll love your object oriented result.