code: private static WyilFile compile(List<Path.Entry<WhileyFile>> sources, Path.Entry<WyilFile> target) throws IOException {
  		// Read target WyilFile. This may have already been compiled in a previous run
  		// and, in such case, we are invalidating some or all of the existing file.
  		WyilFile wyil = target.read();
  		// Parse all modules
  		for(int i=0;i!=sources.size();++i) {
  			Path.Entry<WhileyFile> source = sources.get(i);
  			WhileyFileParser wyp = new WhileyFileParser(wyil, source.read());
  			// FIXME: what to do with module added to heap? The problem is that this might
  			// be replaced a module, for example.
  			wyil.getModule().putUnit(wyp.read());
  		}
  		//
  		return wyil;
  	}
docs: Compile one or more WhileyFiles into a given WyilFile
  
  @param source The source file being compiled.
  @param target The target file being generated.
  @return
  @throws IOException