Parsing question

Question

Hi All

I am creating a scripting language to be used to create web pages, but don't know exactly where to begin.

I have a file that looks like this:

---

mylanguagename(main) {
       OnLoad(protected) {
              Display(img, text, link);
       }

       Canvas(public) {
              Image img: "Images\my_image.png";
                    img.Name: "img";
                    img.Border: "None";
                    img.BackgroundColor: "Transparent";
                    img.Position: 10, 10;

              Text text: "This is a multiline str#ning. The #n creates a new line.";
                   text.Name: text;
                   text.Position: 10, 25;

              Link link: "Click here to enlarge img.";
                   link.Name: "link";
                   link.Position: 10, 60;

                   link.Event: link.Clicked;
       }

       link.Clicked(sender, link, protected) {
              Image img: from Canvas.FindElement(img);
                    img.Size: 300, 300;
       }
}

... and I need to be able to make that text above target the Windows Scripting Host. I know this can be done, because there used to be a lot of Docs on it around the net a while back, but I cannot seem to find them now.

Can somebody please help, or get me started in the right direction?

Thanks

Answer 1

So you want to translate C# programs to JavaScript? Script# can do this for you.

Answer 2

You're making a domain-specific language which does not exist. You want to translate to another language. You will need a proper scanner and parser. You've probably been told to look at antlr. yacc/bison, or gold. What went wrong with that?

And as an FYI, it's a fun exercise to make new languages, but before you do for something like this, you might ask a good solid "why? What does my new language provide that I couldn't get any other (reasonable) way?"

Answer 3

You obviously need machinery designed to translate langauges: parsing, tree building, pattern matching, target-language tree building, target-language prettyprinting. You can try to do all of this with YACC (or equivalents), but you'll discover that parsing is only a small part of a full translator. This means there's a lot more work to do than just parsing, and that takes time and effort.

Our DMS Software Reengineering Toolkit is a commercial solution to building full translators for relatively modest costs.

If you want to do it on your own from the ground up as an exercise, that's fine. Just be prepared for the effort it really takes.

One last remark: designing a complete language is hard if you want to get a nice result.

Answer 4

Languages similar to C# are not easy to parse - there are some naturally left-recursive rules. So you have to use a parser generator that can deal with them properly. ANTLR fits well.

If PEG fits better, try this: http://www.meta-alternative.net/mbase.html

Answer 5

Rather than write your own language and then run a translator to convert it into Javascript, why not extend Javascript to do what you want it to do?

Take a look at jQuery - it extends Javascript in many powerful ways with a very natural and fluent syntax. It's almost as good as having your own language. Take a look at the many extensions people have created for it too, especially jQuery UI.

Answer 6

The thing to understand about parsing and language creation is that writing a compiler/interpreter is primarily about a set of data transformations done to an input text.

Generally, from an input text you will first translate it into a series of tokens, each token representing a concept in your language or a literal value.

From the token stream, you will generally then create an intermediate structure, typically some kind of tree structure describing the code that was written.

This tree structure can then be validated or modified for various reasons, including optimization.

Once that's done, you'll typically write the tree out to some other form - assembly instructions or even a program in another language - in fact, the earliest versions of C++ wrote out straight C code, which were then compiled by a regular C compiler that had no knowledge of C++ at all. So while skipping the assembly generation step might seem like cheating, it has a long and proud tradition behind it :)

I deliberately haven't gotten into any suggestions for specific libraries, as understanding the overall process is probably much more important than choosing a specific parser technology, for instance. Whether you use lex/yacc or ANTLR or something else is pretty unimportant in the long run. They'll all (basically) work, and have all been used successfully in various projects.

Even doing your own parsing by hand isn't a bad idea, as it will help you to learn the patterns of how parsing is done, and so then using a parser generator will tend to make more sense rather than being a black box of voodoo.

Answer 7

I don't wan to be rude... but why are you doing this?

Creating a parser for a regular language is a non-trivial task. Just don't do it.

Why don't you just use html, javascript and css (and jquery as someone above suggested)

If you don't know where to begin, then you probably don't have any experience of this kind and probably you don't have a good reason, why to do this.

I want to save you the pain. Forget it. It's probably a BAD IDEA!

M.

Answer 8

1. Check out Constructing Language Processors for Little Languages. It's a very good intro I believe. In fact I just consulted my copy 2 days ago when I was having trouble with my template language parser.

2. Use XML if at all possible. You don't want to fiddle with a lexer and parser by hand if you want this thing in production. I've made this mistake a few times. You end up supporting code that you really shouldn't be. It seems that your language is mainly a templating language. XML would work great there. Just as ASPX files are XML. Your server side blocks can be written in Javascript, modified if necessary. If this is a learning exercise then do it all by hand, by all means.

I think writing your own language is a great exercise. So is taking a college level compiler writing class. Good luck.

Answer 9

Assuming you are really dedicated to do this, here is the way to go. This is normally what you should do: source -> SCANNER -> tokens -> PARSER -> syntax tree

1) Create a scanner/ parser to parse your language. You need to write a grammar to generate a parser that can scan/parse your syntax, to tokenize/validate them.

I think the easiest way here is to go with Irony, that'll make creating a parser quick and easy. Here is a good starting point

http://www.codeproject.com/KB/recipes/Irony.aspx

2) Build a syntax tree - In this case, I suggest you to build a simple XML representation instead of an actual syntax tree, so that you can later walk the XML representation of your DOM to spit out VB/Java Script. If your requirements are complex (like you want to compile it or so), you can create a DLR Expression Tree or use the Code DOM - but here I guess we are talking about a translator, and not about a compiler.

But hey wait - if it is not for educational purposes, consider representing your 'script' as an xml right from the beginning, so that you can avoid a scanner/parser in between, before spitting out some VB/Java script/Html out of that.