Re: Getting rid of backups in flex.

Danny Dube wrote:
>
> Adding the following error-catching regular expression:
> ..
> (as someone suggested previously) is not correct because this
> expression would take precedence on the normal regular expressions
> when the input would start with a single-digit integer. For example,
> if the input starts with:
> 9),...
> the automaton would do a match of length 2 and return `tError' instead
> of matching the length 1 string "9" and returning `tInt'.


I think that was my suggestion, and it contained a typo. What I really
advocate is a single final rule


. return yytext[0]


to catch (a) all single-char special chars and (b) all lexical errors,
which are handed to the parser to deal with as syntax errors. Apart from
keeping the size of the state machine down, you get the benefit of the
parser's error-recovery if any, rather than just lamely printing out
'illegal character %c'.


EJP

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