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Metaprogramming

Create a program that writes programs, an interesting tool for optimizing time, generating automated code. I didn’t exactly know what metaprogramming was until today, while reading the article I remembered a program I wrote a while ago, called WAV shifter (https://github.com/k3ll3x/WAV-shifter/), the purpose of this code is to generate algorithmic music using the C language, an endless iterator, and bitwise operators. By looking at the code I see that there exists 3 source codes, play.sh, wavsh.c, wavsh.py; play.sh is a bash script that executes the compiled c file with an input audio file(that in a way is going to be modified), after that a wav file will be generated, and this is played by the aplay command. Note, this code only works in Unix systems, with pulseaudio installed. The Python file, wavsh.py, takes the source file wavsh.c and replaces a specific space on the source code, changing that with the input string given at the python program, that string could be a variable t modified with bitwise operators, such as t>>1; t<<&t; t|t; t^t; and so on. After that it takes the new generated code and compiles that with the GCC Compiler. Now the output audio file can be played.

The python script looks like this:

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#!/usr/bin/env python
import subprocess
import signal
import sys

def signal_handler(sig, frame):
        print('You pressed Ctrl+C!')
        sys.exit(0)

def main():
 with open('wavsh.c', 'r') as myfile:
  data=myfile.read()#.replace('\n', '')
 input = raw_input('ncmd: ');
 ndata = data.replace("$",input)
 text_file = open("wwavsh.c", "w")
 text_file.write("%s" % ndata)
 text_file.close()
 ncmd = 'gcc wwavsh.c -lm'.split()
 rc = subprocess.call(ncmd);
 ncmd = 'rm wwavsh.c'.split()
 rc = subprocess.call(ncmd);
 ncmd = './play.sh'
 signal.signal(signal.SIGINT, signal_handler)
 rc = subprocess.call(ncmd.split());
 signal.pause()

 print('Press Ctrl+C')

main()

This application (WAV Shifter) is a very simple program, and very easy to use, the utilization from other programming languages in order to generate code (other programming language) is made, it is interesting this kind of used metaprogramming although I didn’t actually know it was that. Of course this is a simple example and is just a test project, but metaprogramming is very powerful and very useful.

References:

http://34.212.143.74/s201911/tc3049/metaprogramming.html
http://hilite.me/

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