(flex.info.gz) Why cant I use fast or full tables with interactive mode?

Info Catalog

(flex.info.gz) How can I make REJECT cascade across start condition boundaries?

(flex.info.gz) FAQ

(flex.info.gz) How much faster is -F or -f than -C?

 
 Why can't I use fast or full tables with interactive mode?
 ==========================================================
 
 One of the assumptions flex makes is that interactive applications are
 inherently slow (they're waiting on a human after all).  It has to do
 with how the scanner detects that it must be finished scanning a token.
 For interactive scanners, after scanning each character the current
 state is looked up in a table (essentially) to see whether there's a
 chance of another input character possibly extending the length of the
 match.  If not, the scanner halts.  For non-interactive scanners, the
 end-of-token test is much simpler, basically a compare with 0, so no
 memory bus cycles.  Since the test occurs in the innermost scanning
 loop, one would like to make it go as fast as possible.
 
    Still, it seems reasonable to allow the user to choose to trade off
 a bit of performance in this area to gain the corresponding
 flexibility.  There might be another reason, though, why fast scanners
 don't support the interactive option.
 

Info Catalog

(flex.info.gz) How can I make REJECT cascade across start condition boundaries?

(flex.info.gz) FAQ

(flex.info.gz) How much faster is -F or -f than -C?