Lookahead

Sometimes in the rules section you want to do one thing if the text following a token is A, and another thing if the following text is B. Example: consider this input:

newborn: Sara

newborn: Pete

After we get the token "newborn: " we want to lookahead. It the

following text is Sara or Linda or Julie or Barbara then we want

to print "It's a girl!". If the following text is Jonathan or Pete

or George then we want to print "It's a boy!".

Sometimes in the rules section you want to do one thing if the text following a token is A, and another thing if the following text is B. Example: consider this input: