Like other combinatory parsers, we used functional structures available in .Net and specially High Order Functions in order to design Ve Parser; however, the functions, which are used in the Ve parser, have a different structure in comparison with others; and consequently, a number of remarkable merits are provided. For instance, this parser is by far the simplest and easiest to understand among other combinatory parsers and it has the possibility of parallel processing for choice combinators. On the other hand, the usage of object-oriented approaches will lead to avoid of restrictions of pure functional programming. Moreover, Ve Parser has the ability of generating Abstract Syntax Tree in an integrated way and the output of parsing will be a concrete conceptual object.
What is a Combinatory Parser How Ve Parser works?
The only
jargon I used in the project and even in the source codes are 'Combinator
Parser' and 'Lexer'. I dont want to make it more complex by explaining what a
combinator parser is, but if you are curious you can see its page in wiki
pedia. You see, its a little complicated
subject but Ve Parser is much simpler that the name 'combinatory parser'
suggests. So instead of describing what is a Combinatory Parser I will describe
how Ve Parser works:Ve Parser is defined only a delegate type named Parser which has no input and has a boolean output. Parser is a delegate type, so variables of type Parser are functions that can be executed, when a Parser executes it returns a boolean value. The result value from a Parser specifies if it was successful for or not.
Then there is ParserBase class which is an abstract class you have to derive from. When you derive from it you have to implement the abstract method -GetRootParser-. To implement this GetRootParser the BaseParser class provided you with a set of functions which all of them get inputs of type Parser and produce a Parser as result, as long as all of them have the output type of Parser and all of them have input of type Parser they can used combined toghether to form a more mature parser from a more basic parser and finaly make a root parser. For example it would look like 'seq(oneOrMore(....),any(...),seq(any(zeroOrMore(...))))'. Here the seq function is being called by passing the result of oneOrMore parser, any and seq. Then seq parser returns a parser as result.
Features
- Simple to use. Simple to learn. Although hard to understand how it works internally.
- No dependency on any grammar language, only pure C# code can be used to design and implement a parser.
- Rich grammar authoring preset. The ParserBase is shiped with a whole bunch of useful parser combinators like : seq, any, zeroOrMore, zeroOrOne, oneOrMore, zeroOrMoreAny, zeroOeMoreSeq, oneOrMoreAny, oneOrMoreSeq and deleimitedList and mixture.
- Producing output result from the parsed content. (A.k.a Abstract Syntax Tree generation).
- Extensible. Although there are lots of useful combinators you can wrote your own combinators to the library. I am looking to hearing from you about any new combinator that you may suggest.
- Probably fast, if you wrote a neat grammar it should be fast. I need to evaluate performance more percisely to claim about it speed.
- Grammar debugging. Yes that's it, you can monitor the executation of the parser, and also you can put breakpoints in your parser code to see how it is performing. (_Although this features require some improvements, so the next version would be even better).
- Shiped with a default Lexer.
- Lightweight library, with no dependency to any other library. Just you need .Net 4 to use it. And itself is only a couple of essential classes and some other helper classes.
Sample Code
Probably a good way to describe the library is a sample code of how a Parser using Ve Parser would look like:Here is a small part of a sample parser for C# language (to make it more understandable and to make it smaller only a part of the whole parser is included):
// Define some keywords using the Keyword_of function and assign it to Parser deleagates Parser @public = Keyword_of("public"); Parser @private = Keyword_of("private"); Parser @protected = Keyword_of("protected"); Parser @get = Keyword_of("get"); Parser @set = Keyword_of("set"); Parser @enum = Keyword_of("enum"); Parser @class = Keyword_of("class"); Parser @internal = Keyword_of("internal"); Parser @using = Keyword_of("using"); Parser @namespace = Keyword_of("namspace"); // Combine some basic parsers using any and zeroOrOne combinators and create a more high level parser Parser member_access_level = zeroOrOne(any( set_choice("access_level", "public", @public), set_choice("access_level", "private", @private), set_choice("access_level", "protected", @protected), set_choice("access_level", "internal", @internal), set_choice("access_level", "protectedinternal", seq(@protected, @internal)))); // Combine parsers using seq function Parser property_get = seq(@get, Symbol_of("{"), zeroOrMore(statement), Symbol_of("}")); Parser property_set = seq(@set, Symbol_of("{"), zeroOrMore(statement), Symbol_of("}"));
