Brainf**k to Ruby interpreter -- v3

Question

Previous iteration.

I think this is about as good as it's gonna get, but just for kicks, let's do one more round of iterations.

As before, it's a very simple substitution from Brainfuck to Ruby, with fancy things like joining duplicate lines into one and indentation.

Some things that bug me:

• The regex (/\++|-+|<+|>+|[.,\[\]]/) feels like it can be simplified, but I can't figure out how.
• I feel like the map can be simplified, but I can't figure out how.
• The constant repetition of #{' ' * indent_level} bugs me, but I can't see how to get rid of it.
• indent_level being declared outside of the scope of each feels like an anti-pattern, but AFAICT there's no better way to do it.

input_file, output_file = ARGV
code = IO.read(input_file).delete('^+-<>.,[]')
open(output_file, File::CREAT | File::WRONLY) do |output|
 output.puts <<-END.gsub(/^[ \t]*\||\s*#@.*$/, '')
 |#!/usr/bin/env ruby
 |class Mem < Hash #@ Hash because it's more memory-efficient and allows negative values.
 | def initialize; super(0); end
 | def []=(i, val); super(i, val & 255); end
 |end
 |data = Mem.new
 |pointer = 0
 END
 indent_level = 0
 code.scan(/\++|-+|<+|>+|[.,\[\]]/)
 .map do |string|
 case string[0]
 when '+' #String of "+"
 next "#{' ' * indent_level}data[pointer] += #{string.length}"
 when '-' #String of "-"
 next "#{' ' * indent_level}data[pointer] -= #{string.length}"
 when '<' #String of "<"
 next "#{' ' * indent_level}pointer -= #{string.length}"
 when '>' #String of ">"
 next "#{' ' * indent_level}pointer += #{string.length}"
 when '[' #Single "["
 ret = "#{' ' * indent_level}until data[pointer] == 0"
 indent_level += 1
 next ret #Split it so that it's clear that indent is increased *after* the line
 when ']' #Single "]"
 indent_level -= 1
 next "#{' ' * indent_level}end"
 when ',' #Single ","
 next "#{' ' * indent_level}data[pointer] = $stdin.readbyte"
 when '.' #Single "."
 next "#{' ' * indent_level}putc data[pointer]"
 end
 end.each { |line| output.puts(line) }
end

• Jörg W Mittag: BTW: this is a compiler, not an interpreter.

Answer 1

I'm not 100% sure this works in Ruby, but can you use constants with string interpolation? This string is repeated a lot. I doubt it will ever change, but if it does, it would be nice to only have to change it once.

"#{' ' * indent_level}data[pointer]"

Could be #{' ' * indent_level}#{DATA}.

• anon: I'm not quite sure what you mean by "can you use constants with string interpolation?"
• RubberDuck: Can you inject a constant string value into another string using interpolation? I'm sure you can. I'm just not sure you can.
• anon: Oh, like "#{'test'} test"? Yes, that's possible. I don't see why you'd do it though.
• RubberDuck: Because this string (data[pointer]) is repeated several times. If you would ever have a reason to change it. You'd only have to change it once.
• anon: And when would I ever need to change it?