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From: merlyn@iwarp.intel.com (Randal Schwartz)
Newsgroups: comp.lang.c,comp.unix.wizards
Subject: Re: Lex and initial start conditions
Message-ID: <1990May31.161800.11133@iwarp.intel.com>
Date: 31 May 90 16:18:00 GMT
References: <6342@crabcake> <1990May30.174745.1161@csrd.uiuc.edu> <116@bohra.cpg.oz>
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Reply-To: merlyn@iwarp.intel.com (Randal Schwartz)
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Organization: Stonehenge; netaccess via Intel, Beaverton, Oregon, USA
Lines: 36
In-Reply-To: ejp@bohra.cpg.oz (Esmond Pitt)

In article <116@bohra.cpg.oz>, ejp@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@iwarp.intel.com ...!any-MX-mailer-like-uunet!iwarp.intel.com!merlyn |
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