F bf(source)
   V tape = DefaultDict[Int, Int]()
   V cell = 0
   V ptr = 0
   L ptr < source.len
      S source[ptr]
         ‘>’
            cell++
         ‘<’
            cell--
         ‘+’
            tape[cell]++
         ‘-’
            tape[cell]--
         ‘.’
            :stdout.write(Char(code' tape[cell]))
         ‘,’
            tape[cell] = :stdin.read(1).code
         ‘[’
            I tape[cell] == 0
               V nesting_level = 0
               L
                  S source[ptr]
                     ‘[’
                        nesting_level++
                     ‘]’
                        I --nesting_level == 0
                           L.break
                  ptr++
         ‘]’
            I tape[cell] != 0
               V nesting_level = 0
               L
                  S source[ptr]
                     ‘[’
                        I --nesting_level == 0
                           L.break
                     ‘]’
                        nesting_level++
                  ptr--
      ptr++

bf(‘++++++++[>++++[>++>+++>+++>+<<<<-]>+>+>->>+[<]<-]>>.>---.+++++++..+++.>>.<-.<.+++.------.--------.>>+.>++.’)