BFFB

BFFB (Brainfuck fucks brains) is a joke language (devised by User:Feuermonster, 2012) whose acronym incidentally is a palindrome. BFFB programs are essentially brainfuck programs with just one little restriction. Due to popular request BFB is an abbreviation for BFFB, incidentally both are palindromic. BFB is the official file extension for BFFB programs.

Restriction

Any given program P consisting of a list of instructions L is a valid program:

 iff P ∈ BF where BF is the set of all valid brainfuck programs.
and
 iff L = mirror(L)

Where mirror is a function "mirroring" characters

[ → ]
] → [
> → <
< → >
+ → +
- → -
. → .
, → ,

Example:

[><] | [><] 

An easy way to turn brainfuck programs into valid BFFB programs would be to put

[-]+[]

at the end of the brainfuck program and then mirror it.

Examples

[-]

is a perfectly valid BFFB program.

[>]

is not a valid BFFB program.

Cat Program

,[.,][,.],

The second part of the program never runs because the first loop never ends.

Implementations

This is an implementation in Python. It assumes all non-BF characters in the original code are comments and only analyzes the BF characters for symmetry purposes.

# runs language from https://esolangs.org/wiki/BFFB
# textfile indicates whether the string is a textfile
# starting_input indicates what the starting input should be, in case it shouldn't be taken from the text
def run_bffb(rawcode: str, textfile=False, starting_input='') -> None:
    pointer = 0  # for instructions
    location = 0  # for tape
    tape = [0]
    input_string = starting_input  # allows multiple inputs to happen easily

    if textfile:
        with open(rawcode, 'r') as s:
            code = [char for char in ''.join(s.readlines()) if char in set('+-><,.[]')]
    else:
        code = [char for char in rawcode if char in set('+-><,.[]')]

    mirror = {'+': '+',
              '-': '-',
              '>': '<',
              '<': '>',
              ',': ',',
              '.': '.',
              '[': ']',
              ']': '['}

    for x in range(len(code)):
        first, last = code[x], code[len(code) - 1 - x]
        if mirror[first] != last:
            raise SyntaxError(f'{first} is not the mirror image of {last}')

    corresponding_bracket = {}  # dictionary where the values are the corresponding bracket positions of the keys
    bracket_stack = []  # acts as a stack for the last bracket

    for num, char in enumerate(code):
        if char == '[':
            bracket_stack.append(num)
        elif char == ']':
            if len(bracket_stack) <= 0:
                raise ValueError('unmatched ]')
            corresponding_bracket[num] = bracket_stack[-1]
            corresponding_bracket[bracket_stack[-1]] = num
            bracket_stack.pop()
    if len(bracket_stack) != 0:
        raise ValueError('unmatched [')

    while pointer < len(code):
        if code[pointer] == '>':
            location += 1
            if location == len(tape):
                tape.append(0)
        elif code[pointer] == '<':
            if location <= 0:
                raise ValueError('Cannot move left from position 0')
            location -= 1
        elif code[pointer] == '+':
            tape[location] = (tape[location] + 1) % 256
        elif code[pointer] == '-':
            tape[location] = (tape[location] - 1) % 256
        elif code[pointer] == '.':
            print(chr(tape[location]), end='')
        elif code[pointer] == ',':
            if input_string == '':
                input_string = input(">>")
            if len(input_string) > 0:
                tape[location] = ord(input_string[0])
                input_string = input_string[1:]
        elif code[pointer] == '[':
            if tape[location] == 0:
                pointer = corresponding_bracket[pointer]
        elif code[pointer] == ']':
            if tape[location] != 0:
                pointer = corresponding_bracket[pointer]
        pointer += 1