I am trying to define a non terminal symbol in a LALR(1) grammar (with CUP parser). It is requested that
the <code> token must appear exactly twice,
while the <hour> token must appear at least once.
In the end I came up with this definition:
section ::= hour_l CODE SC hour_l CODE SC hour_l ;
hour_l ::= /* epsilon */
| hour_l HOUR SC ;
where SC
is a separator (semicolon) between tokens and hour_l
is the non terminal symbol for hour's list.
This solution has a problem: HOUR
can be absent, because epsilon
can be reduced from hour_l
.
Is there a clever solution other than specifying all possibilities or using the semantic capabilities of CUP (ie. putting a counter of how many times HOUR
is present in section
)? I'd prefer not to use semantics in order to achieve this; in fact, it seems to me this is syntax related.
Thanks
HOUR
). $\endgroup$