Lex and initial start conditions

[Randal Schwartz]

In article <116 at bohra.cpg.oz>, ejp at bohra (Esmond Pitt) writes:
| There are two even simpler ways.
| 
| Instead of effectively changing the initial condition to <Text>, either:
| 
| 1. Ensure each start-state is equipped with enough rules to handle any
| possible input, and, as the documentation does state, place all the
| unlabelled rules after all the labelled rules, and/or
| 
| 2. Label all the rules you only want applied in the INITAL state with
| <INITIAL>, so they won't be applied as defaults in other states.
| 
| Placing non-labelled rules before labelled rules is probably the single
| most common error in writing LEX scripts, even after 15 years.
| 
| I don't know why.

Because it is insufficient.  It's not "first match", but "longest
match" that determines rule triggering.  ("first match" applies when
the rules have the same length.)

...
<FOO>a	{ something; }
...
ab	{ something_else; }
...

will match the "something_else" clause if "ab" is seen, even in state
"FOO".  I know... this bit me once.

Just another lex hacker,
-- 
/=Randal L. Schwartz, Stonehenge Consulting Services (503)777-0095 ==========\
| on contract to Intel's iWarp project, Beaverton, Oregon, USA, Sol III      |
| merlyn at iwarp.intel.com ...!any-MX-mailer-like-uunet!iwarp.intel.com!merlyn |
\=Cute Quote: "Welcome to Portland, Oregon, home of the California Raisins!"=/