Re: Grammars with semantics

haberg@matematik.su.se (Hans Aberg)
27 Apr 2003 16:46:04 -0400

          From comp.compilers
Related articles
Grammars with semantics haberg@matematik.su.se (2003-04-20)
Re: Grammars with semantics rda@lemma-one.com (Rob Arthan) (2003-04-27)
Re: Grammars with semantics haberg@matematik.su.se (2003-04-27)
Re: Grammars with semantics haberg@matematik.su.se (2003-05-06)
| List of all articles for this month |
From: haberg@matematik.su.se (Hans Aberg)
Newsgroups: comp.compilers
Date: 27 Apr 2003 16:46:04 -0400
Organization: Mathematics
References: 03-04-067 03-04-100
Keywords: parse
Posted-Date: 27 Apr 2003 16:46:03 EDT

>> Take the "calculator" grammar G = (T, N, P, E), terminals T = {i, `+',
>> `*', `(', `)'}, nonterminals N = {E, T, F}, sentence symbol E, and the
>> set of productions P containing:
>> P_1: E -> T
>> P_2: E -> E `+' T
>> P_3: T -> F
>> P_4: T -> T `*' F
>> P_5: F -> i
>> P_6: F -> `(' F `)'


>> The expression i + i*i has several parses, for example the leftmost (as in
>> LL, top-down, parsing) and rightmost (as in LR, bottom-up parsing):


>> So this grammar is ambiguous,


>No, it's not. Top-down and bottom-up parsing produce the same parse-trees,
>but they construct the nodes in different orders.


I forgot to think about the parse trees. How silly! :-)


Thank you for pointing this out to me.


    Hans Aberg * Anti-spam: remove "remove." from email address.
                                    * Email: Hans Aberg <remove.haberg@member.ams.org>
                                    * Home Page: <http://www.math.su.se/~haberg/>
                                    * AMS member listing: <http://www.ams.org/cml/>


Post a followup to this message

Return to the comp.compilers page.
Search the comp.compilers archives again.