$ include "seed7_05.s7i";

const proc: brainF (in string: source, inout file: input, inout file: output) is func
  local
    var array char: memory is 100000 times '\0;';
    var integer: dataPointer is 50000;
    var integer: instructionPointer is 1;
    var integer: nestingLevel is 0;
  begin
    while instructionPointer <= length(source) do
      case source[instructionPointer] of
        when {'>'}: incr(dataPointer);
        when {'<'}: decr(dataPointer);
        when {'+'}: incr(memory[dataPointer]);
        when {'-'}: decr(memory[dataPointer]);
        when {'.'}: write(output, memory[dataPointer]);
        when {','}: memory[dataPointer] := getc(input);
        when {'['}: # Forward if zero at dataPointer
          if memory[dataPointer] = '\0;' then
            nestingLevel := 1;
            repeat
              incr(instructionPointer);
              case source[instructionPointer] of
                when {'['}: incr(nestingLevel);
                when {']'}: decr(nestingLevel);
              end case;
            until nestingLevel = 0;
          end if;
        when {']'}: # Backward if non-zero at dataPointer
          if memory[dataPointer] <> '\0;' then
            nestingLevel := 1;
            repeat
              decr(instructionPointer);
              case source[instructionPointer] of
                when {'['}: decr(nestingLevel);
                when {']'}: incr(nestingLevel);
              end case;
            until nestingLevel = 0;
          end if;
      end case;
      incr(instructionPointer);
    end while;
  end func;

const proc: brainF (in string: source) is func
  begin
    brainF(source, IN, OUT);
  end func;

const proc: main is func
  begin
    brainF("++++++++++[>+++++++>++++++++++>+++>+<<<<-]>++.>+.+++++++..+++.>++.<<+++++++++++++++.>.+++.------.--------.>+.>.");
  end func;