context-free-grammar

问题 I have this very simple grammar: grammar DLR; dlr : c 'sub' c ; c : CN | 'not' c | c 'and' c | c 'or' c ; CN : [A-Z]+ ; WS : [ \t\r\n]+ -> skip ; // skip spaces, tabs, newlines When I generate the java code with antlr4 command, I got the java interface DLRBaseListener: public class DLRBaseListener implements DLRListener { @Override public void enterDlr(DLRParser.DlrContext ctx) { } @Override public void exitDlr(DLRParser.DlrContext ctx) { } @Override public void enterC(DLRParser.CContext ctx)

问题 I am writing a simulator, and would like to run studies by invoking a lot of instances of the simulator, using different sets of command-line arguments. I have read this question and several others, and they seem close, but I'm actually not looking for random data fulfilling a particular regex, I would like the set of all strings that match the regex. An example input file would look something like this: myprogram.{version1|version2} -arg1 {1|2|4} {-arg2|} or: myprogram.{0} -arg1 {1} {2} 0:

问题 Closed. This question is off-topic. It is not currently accepting answers. Want to improve this question? Update the question so it's on-topic for Stack Overflow. Closed 6 years ago . How can I show that the following language is (not) context-free? The argument that it's not regular goes as follows. I suspect this language to be context-free... The reason why I think this, is because L = {a n b m c {n+m} | n,m >= 0} is context-free. A proof for this can be found at http://cg.scs.carleton.ca/

问题 I'm trying to figure out how to do parse trees correctly to show whether a grammar is ambiguous or not. my grammar is S -> xSy | ySx | SS | e any help would be great. thanks in advance below is my crack at it... S / \ / \ x y / \ / \ x x y y 回答1: As a hint, pretty much any grammar with a production of the form S → SS will be ambiguous, because if you want to produce three S nonterminals you can do so in two ways: S S / \ / \ S S S S / \ / \ S S S S Assuming those S's can actually produce

问题 Can someone explain to me what a context free grammar is? After looking at the Wikipedia entry and then the Wikipedia entry on formal grammar, I am left utterly and totally befuddled. Would someone be so kind as to explain what these things are? I am wondering this because I wish to investigate parsing, and also on the side, the limitation of a regex engine. I'm not sure if these terms are directly programming related, or if they are related more to linguistics in general. If that is the case

问题 Reading Chomsky hierarchy ... ... I know regexp can't parse type-2 grammars (context-free grammars), and also type-1 and type-0. Can regular expressions parse/catch ALL type-3 grammars (regular grammars)? 回答1: Yes, provided they support alternation, concatenation, and the Kleene star. This is the case for regexes of the PCRE (Perl/Java/JavaScript/PHP/...) type: alternation is implemented by ((...)|(...)) , concatenation by (...)(...) , and the Kleene star by (...)* . (There are a few other

问题 I'm reviewing my notes for my course on theory of computation and I'm having trouble understanding how to complete a certain proof. Here is the question: A = {0^n 1^m 0^n | n>=1, m>=1} Prove that A is not regular. It's pretty obvious that the pumping lemma has to be used for this. So, we have |vy| >= 1 |vxy| <= p (p being the pumping length, >= 1) uv^ixy^iz exists in A for all i >= 0 Trying to think of the correct string to choose seems a bit iffy for this. I was thinking 0^p 1^q 0^p, but I

问题 I tried error reporting in following manner. @members{ public String getErrorMessage(RecognitionException e,String[] tokenNames) { List stack=getRuleInvocationStack(e,this.getClass().getName()); String msg=null; if(e instanceof NoViableAltException){ <some code> } else{ msg=super.getErrorMessage(e,tokenNames); } String[] inputLines = e.input.toString().split("\r\n"); String line = ""; if(e.token.getCharPositionInLine()==0) line = "at \"" + inputLines[e.token.getLine() - 2]; else if(e.token

问题 Specifically, I noticed that the language of regular expressions itself isn't regular. So, I can't use a regular expression to parse a given regular expression. I need to use a parser since the language of the regular expression itself is context free. Is there any way regular expressions can be represented in a way that the resulting string can be parsed using a regular expression? Note: My question isn't about whether there is a regexp to match the current syntax of regexes, but whether

问题 I'm looking for a CFG parser implemented with Java. The thing is I'm trying to parse a natural language. And I need all possible parse trees (ambiguity) not only one of them. I already researched many NLP parsers such as Stanford parser. But they mostly require statistical data (a treebank which I don't have) and it is rather difficult and poorly documented to adapt them in to a new language. I found some parser generators such as ANTRL or JFlex but I'm not sure that they can handle