At 08:35 12/11/2009, Kaleb Pederson wrote:
>Is there an easy way to enforce in the grammar that a lexical
token
>must be present a certain number of times?
>
>For example, with TOKEN{x,y} as you might see in an extended
>regular expression, it would require that TOKEN be present at
>minimum x times and at most y times.
The best way to do it is to use validation code:
rule: (t+=TOKEN)+ { /* check $t and throw an error if the wrong
number appears */ };
You can also do this purely syntactically, but there isn't a
"nice" syntax for it and it won't produce as useful an error to
the user:
// TOKEN{3,5}
rule: TOKEN TOKEN TOKEN (TOKEN TOKEN?)?;
This sort of requirement is fairly unusual for a language
specification, though.
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