Thank you for being so patient to a newbie. It's just homework and I think it's not that deep because the course is only about Perl. I'm interested in parsing, but I haven't learnt much about it yet.
2011/4/25 Shlomi Fish <shlo...@iglu.org.il> > Hi "Z", > > you replied to me in private (unintentionally, I presume), so I'm CCing the > list on my reply (I hope it's OK). > > On Monday 25 Apr 2011 12:07:54 z sway wrote: > > Hi,sorry I hadn't said it clearly,what I want to do is to generate a LOL > > from an expression and try* *not to use any extra modules. > > OK, one thing you should realise is that, to quote my late grandfather, > Perl > without CPAN is like a cat without whiskers[whiskers]. While it sometimes > makes sense to reduce dependencies[Deps], often many modules on CPAN are > self- > contained, or have very few dependencies and you can stick them in one > place > and forget about them or pack them in PAR. See: > > http://www.shadowcat.co.uk/blog/matt-s-trout/but-i-cant-use-cpan/ > > (Matt S. Trout has an offensive and insulting style, so you have been > warned, > but he still says wise things of substance.). > > Anyway, you can put one of the parser generators on your system, and I > think > byacc-perl generates self-contained Perl code. > > > So far i've only got an idea that spilt the expression into a list_A,in > > which each element is a number or"+*()",use list_B as a stack,pop from > > list_A,push to list_B under some rules,finally got the tree in list_B. > > > > I think my method is a bit complicated,there should be a easier one even > if > > can't detect some mistakes like (5+)2)*5 or 6++7*8 > > > > Implementing your own Parse-Recdescent (or worse LALR/GLR/etc.) parser is > prone to errors and inadvisable, especially if you don't have a lot of > theoretical background. Unless this is homework in compilation theory or a > similar course (which most universities don't really do in Perl, for better > or > for worse), then please use a parser generator, in case you're interested > in > writing your code quickly and correctly, rather than re-inventing your own > square wheel (and trust me - it will be square). > > If you *are* interested in learning more about compiler theory and parsing, > then I liked the Dragon book (read the green one I think, but there's > already > a newer Purple dragon one which should be better), and while it has some > issues, is pretty good: > > http://en.wikipedia.org/wiki/Compilers:_Principles,_Techniques,_and_Tools > > There are many other online and offline books, tutorials and resources (on > http://www.wikibooks.org/ / etc.), and you should be good to go. But doing > it > without learning it first is not a good idea. To quote > http://en.wikiquote.org/wiki/Euclid , "There is no royal road to > geometry", > because sometimes various issues in computer science require learning some > theory to do properly. Note though that parsing theory is not *that* hard. > > Sorry for the long post. > > Regards, > > Shlomi Fish > > [whiskers] - I have only understood this sentence later on when I realised > that cats with damaged whiskers lose their balance, and are very non- > functional: > > http://en.wikipedia.org/wiki/Whiskers > > It didn't help that my grandfather said it in Hebrew, using the same word > for > "whiskers" as the Hebrew word for "moustache", which is completely > inessential > for humans to survive. There is an English idiom called "the Cat's > whiskers", > but I think it means more like "the top of the top" or "la creme de la > creme". > > [Deps] - It is discussed here: > > http://www.onlamp.com/pub/a/onlamp/2004/04/08/disaster_recovery.html > > It kinda reminds me of "Can you build a package in one command?" from the > "McConnell test"/"Joel test": > > http://www.joelonsoftware.com/articles/fog0000000043.html > > > -- > ----------------------------------------------------------------- > Shlomi Fish http://www.shlomifish.org/ > Understand what Open Source is - http://shlom.in/oss-fs > > There is no IGLU Cabal! None of them could pass the Turing test. But > strangely > enough a computer program they coded, could. > > Please reply to list if it's a mailing list post - http://shlom.in/reply . >
