@Override
	public Factory<Genotype<IntegerGene>> encoding() {
		return _encoding;
	}
Create a new sentence (list of terminal symbols) codec.

@param cfg the encoding grammar
@param length the length of the chromosome which is used for selecting
       rules and symbols. The input parameter for this function is the
       actual rule. This way it is possible to define the chromosome
       length dependent on the selectable alternatives.
@param generator sentence generator function from a given
       {@link SymbolIndex}
jenetics.ext/src/main/java/io/jenetics/ext/grammar/MultiIntegerChromosomeMapper.java