about.md

MetaFractran is a version of Fractran in which the entire program is encoded in the program file's metadata - specifically, its file name and path.

Say the program file is located in /home/metafractran/7:3/99:98/13:49/39:35/36:91/10:143/49:13/7:11/1:2/91:1/10.mfc. Only the trailing components of the file path that match the regex \d+:\d+ will be kept, and the rest will be ignored. The file name can have an optional extension, which is ignored. The contents of the file do not matter; however, a compliant implementation must verify that the file exists.

This file corresponds to the program 7/3 99/98 13/49 39/35 36/91 10/143 49/13 7/11 1/2 91/1, with a starting number of 10.

MetaFractran was inspired by Folders and, of course, Fractran.

metafractran.py

# An interpreter for the MetaFractran esolang
# In MetaFractran, the contents of the source file do not matter. The metadata of the file (name, path)
# encodes a Fractran program.
# For example, /root/esolangs/metafractran/7:22/11:39/13:35/7.mfc encodes the Fractran program
# 7/22, 11/39, 13/35, with starting number 7.
# At the end of execution, the resulting number is printed.

import sys
import re
import pathlib
import fractions as fr

path = pathlib.Path(sys.argv[1]).resolve()
if not path.is_file():
    print("File does not exist")
    sys.exit(1)

name, *parts = reversed(path.parts)
is_fraction = re.compile(r"^(\d+):(\d+)$")
fractions = []
for i in parts:
    match = is_fraction.match(i)
    if not match:
        break
    num, denom = match.groups()
    fractions.append(fr.Fraction(int(num), int(denom)))
fractions = fractions[::-1] # they were added backwards

is_valid_name = re.compile(r"(\d+)(?:\..*)?")
match = is_valid_name.match(name)
if not match:
    print("File name is not valid")
    sys.exit(1)
    
num = int(match.group(1))

# run the fractran program

def run_fractran(num, fractions):
    while True:
        for i in fractions:
            product = num * i
            if product.denominator == 1:
                num = int(product)
                break
        else:
            return num

print(run_fractran(num, fractions))