Path: csiph.com!1.us.feeder.erje.net!feeder.erje.net!news.misty.com!news.iecc.com!.POSTED.news.iecc.com!nerds-end From: anton@mips.complang.tuwien.ac.at (Anton Ertl) Newsgroups: comp.compilers Subject: Re: ireegular expressions, syntax complexity Date: Wed, 22 Feb 2023 10:55:21 GMT Organization: Institut fuer Computersprachen, Technische Universitaet Wien Sender: johnl@iecc.com Approved: comp.compilers@iecc.com Message-ID: <23-02-061@comp.compilers> References: <23-02-045@comp.compilers> <23-02-047@comp.compilers> <23-02-050@comp.compilers> <29156_1676600565_63EEE4F4_29156_1009_1_23-02-051@comp.compilers> <23-02-052@comp.compilers> <23-02-053@comp.compilers> <23-02-055@comp.compilers> <23-02-059@comp.compilers> Injection-Info: gal.iecc.com; posting-host="news.iecc.com:2001:470:1f07:1126:0:676f:7373:6970"; logging-data="77041"; mail-complaints-to="abuse@iecc.com" Keywords: syntax, lex, comment Posted-Date: 22 Feb 2023 12:03:11 EST X-submission-address: compilers@iecc.com X-moderator-address: compilers-request@iecc.com X-FAQ-and-archives: http://compilers.iecc.com Xref: csiph.com comp.compilers:3400 anton@mips.complang.tuwien.ac.at (Anton Ertl) writes: >anton@mips.complang.tuwien.ac.at (Anton Ertl) writes: >At most one "." in front of at most one "E": [0-9]*[.]?[0-9]*E?[0-9]* >At least one of "." or "E": .*[.E].* >At least one digit in front of and after "E": .*[0-9].*E[0-9]+ There's still a bug here, because that makes "E" non-optional. Let's make it optional: At least one digit, when using E one before and one after: .*[0-9].*(E[0-9]+)? In total: [0-9]*[.]?[0-9]*E?[0-9]*&.*[.E].*&.*[0-9].*(E[0-9]+)? - anton -- M. Anton Ertl anton@mips.complang.tuwien.ac.at http://www.complang.tuwien.ac.at/anton/ [This doesn't seem all that much simpler than the usual approach with alternation, give or take bugs: ([0-9]+\.[0-9]*|\.[0-9]+)(E[0-9]+)?|[0-9]+E[0-9]+ -John]