Programming Forums > Application Development > C++

rwm · Aug 27th, 2007, 2:19 AM

Hey!

I'm trying to write a parser, and I was hoping anyone could suggest/advise?

What i'd like to do is write a generic parser class, without having to derive from this to parse certain files etc

i.e.

(Toggle Plain Text)

...
Parser *parser = new Parser;
parser->Parse("anyformat.txt");
...
parser->Parse("anotherformat.dat");
...

instead of

(Toggle Plain Text)

...
Parser *parser = new AnyFormatParser;
parser->Parse("anyformat.txt");
...
delete parser;
parser = new AnotherFormatParser;
parser->Parse("anotherformat.dat");
...

I don't know what you think about this? Maybe a little irrational? I think it would be nicer to have a "generic" parser class, and just define a "grammar/syntax" for parsing.

So my idea was to create an abstract class, ParseTree, from which I derive certain other parse trees, such as AnyFormatParseTree, AnotherFormatParseTree etc

So the generic parser would use it like:

(Toggle Plain Text)

...
Parser *parser = new Parser;
AnyFormatParseTree afpt;
parser->SetParseTree(afpt);
parser->Parse("anyformat.txt");
...
AnotherFormatParseTree anfpt;
parser->SetParseTree(anfpt);
parser->Parse("anotherformat.dat");
...

The idea is that the user doesnt have to do anything to the ParseTree subclass (unless deriving their own version) in that the ParseTree subclass already contains a "pre-built" parse tree, so all that is required is to pass an instace of ParseTree* to Parser:

etParseTree(...).

What do you think?

Incidentally i'd like to ask a couple of questions about parse trees and parsing in general.

What is the best method to write an extensible parser framework that can be reused as much as possible?

With a parse tree, what we do is construct a tree of characters, so if i had the keywords in a certain file: akeyword, dosomething, blah

The parse tree would contain branches that took paths to the following keywords, or to NULL right?

Would it be a good idea to implement a certain "callback" via function pointer at completion of parsing a keyword?

Or not?

Hope someone can help!

Thanks!

Aug 27th, 2007, 2:19 AM	#1
rwm Professional Programmer Join Date: Jan 2007 Location: Cape Town Posts: 291 Rep Power: 2	Parsing questions. Hey! I'm trying to write a parser, and I was hoping anyone could suggest/advise? What i'd like to do is write a generic parser class, without having to derive from this to parse certain files etc i.e. (Toggle Plain Text) ... Parser parser = new Parser; parser->Parse("anyformat.txt"); ... parser->Parse("anotherformat.dat"); ... ... Parser parser = new Parser; parser->Parse("anyformat.txt"); ... parser->Parse("anotherformat.dat"); ... instead of (Toggle Plain Text) ... Parser parser = new AnyFormatParser; parser->Parse("anyformat.txt"); ... delete parser; parser = new AnotherFormatParser; parser->Parse("anotherformat.dat"); ... ... Parser parser = new AnyFormatParser; parser->Parse("anyformat.txt"); ... delete parser; parser = new AnotherFormatParser; parser->Parse("anotherformat.dat"); ... I don't know what you think about this? Maybe a little irrational? I think it would be nicer to have a "generic" parser class, and just define a "grammar/syntax" for parsing. So my idea was to create an abstract class, ParseTree, from which I derive certain other parse trees, such as AnyFormatParseTree, AnotherFormatParseTree etc So the generic parser would use it like: (Toggle Plain Text) ... Parser parser = new Parser; AnyFormatParseTree afpt; parser->SetParseTree(afpt); parser->Parse("anyformat.txt"); ... AnotherFormatParseTree anfpt; parser->SetParseTree(anfpt); parser->Parse("anotherformat.dat"); ... ... Parser parser = new Parser; AnyFormatParseTree afpt; parser->SetParseTree(afpt); parser->Parse("anyformat.txt"); ... AnotherFormatParseTree anfpt; parser->SetParseTree(anfpt); parser->Parse("anotherformat.dat"); ... The idea is that the user doesnt have to do anything to the ParseTree subclass (unless deriving their own version) in that the ParseTree subclass already contains a "pre-built" parse tree, so all that is required is to pass an instace of ParseTree* to Parser:etParseTree(...). What do you think? Incidentally i'd like to ask a couple of questions about parse trees and parsing in general. What is the best method to write an extensible parser framework that can be reused as much as possible? With a parse tree, what we do is construct a tree of characters, so if i had the keywords in a certain file: akeyword, dosomething, blah The parse tree would contain branches that took paths to the following keywords, or to NULL right? Would it be a good idea to implement a certain "callback" via function pointer at completion of parsing a keyword? Or not? Hope someone can help! Thanks!

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Programming Forums > Application Development > C++

Parsing questions.