2019-08-14

# Introduction

In an effort to both post more than once a year and clean out some silly things from my ~/tmp directory, here’s a quick post about two programming shenanigans. Perhaps unsurprisingly due to its history of jocularity, both originate with Perl.

# Bleach

Damian Conway is a truly prolific member of the Perl community. One of Conway’s less serious contributions is the Acme::Bleach module, famous for being the first Acme module and the first source filter joke module. Acme::Bleach takes programs that look like this:

use Acme::Bleach;
print "Hello world";


and turns them into

use Acme::Bleach;



No, that’s not an error. Through the magic of Perl’s source filters, the above program whose source consists of nothing but one import statement and a bunch of whitespace still prints “Hello world”!

After digging through the source, I decided to try my hand at recreating it in Python:

#!/usr/bin/env python3
"""For really clean programs"""

from functools import reduce
from pathlib import Path
from subprocess import run
from sys import argv

ZERO = ord(" ")
ONE = ord("\t")

def zero_one(x: int) -> bytes:
"""Convert a byte to a series of ZERO and ONE"""
return bytes([ZERO, ONE][(x >> i) & 1] for i in range(7, -1, -1))

def un_zero_one(xs: bytes) -> int:
"""Undo zero_one"""
return reduce(lambda i, x: (i << 1) | int(x == ONE), xs, 0)

def encode(xs: bytes) -> bytes:
"""Use zero_one to encode"""
return b"".join(zero_one(x) for x in xs)

def decode(xs: bytes) -> bytes:
"""Use un_zero_one to decode"""
return bytes(un_zero_one(xs[i : i + 8]) for i in range(0, len(xs), 8))

if __name__ == "__main__":
if len(argv) != 2:
exit("I need a file to bleach")
else:
if any(x not in {ZERO, ONE} for x in XS):
print(encode(XS).decode("ascii"), end="", flush=True)
else:
run(["python3", "-"], input=decode(XS))


Since Python doesn’t have Perl’s source filters, we can’t do everything that Acme::Bleach does, but bleach.py uses the same main trick: source code consists of bytes, as far as computers care, so we can encode and decode them however we want—including using spaces for zeros and tabs for ones. If we have a file called simple.py consisting of print("hello world"), we can say ./bleach.py simple.py > simple_bleached.py. Then running ./bleach.py simple_bleached.py will result in the interpreter printing "hello world".

# D&D

I recently came across a fun post that describes implementing basic dice notation from Dungeons & Dragons in Perl 6. It’s a fun read, so you should definitely check it, but its basic implementation looks like this:

sub infix:<d>(Int $n, Int$max) { (1..$max).pick xx$n }


So one can enter say (3 d 20); and see something like (17 1 12) printed. Haskell has nice support for infix-ing any function by wrapping it in backticks, so I came up with the following dnd.hs:

#!/usr/bin/env stack
-- stack --install-ghc runghc --package random --resolver lts-14.0
module Main where

import Data.Foldable (traverse_)
import System.Random (getStdGen, randomRs)

d :: Word -> Word -> IO [Word]
d n size = take (fromIntegral n) . randomRs (1, size) <\$> getStdGen

main :: IO ()
main = traverse_ (print =<<) [3 d 8, 2 d 20, 1 d 6]


Running it via ./dnd.hs1, I got

[6,6,3]
[10,10]
[2]


Though of course different runs will probably output different results.

1. Assuming of course that you’ve got stack installed. ↩︎