@Override
	public T apply(final T[] args) {
		if (args.length < arity()) {
			throw new IllegalArgumentException(format(
				"Arguments length is smaller than program arity: %d < %d",
				args.length, arity()
			));
		}

		return eval(_tree, args);
	}
Return the underlying expression tree.

@since 4.1

@return the underlying expression tree
jenetics.prog/src/main/java/io/jenetics/prog/op/Program.java