Additive Grammar
A ¨ V | V + A
V ¨ a|b|c|d|e|f|g|h|i|j|k|l|m
|n|o|p|q|r|s|t|u|v|w|x|y|z
Corresponding to the grammar above,
there will be two parse methods:
A()
V()
Each parses from the current point in
the input.