I was reading thru the ADO.NET Data Services Quickstart, because I wanted to understand how it support data updates. The quickstart uses the Customers table from the Northwind sample database, which unlike most of the other tables uses an nchar(5) value as the primary key. Categories, Employees, Orders, Products, Shippers and Suppliers all use an auto-increment integer field for their primary keys.

I only point this out because inserting into Customers is idempotent, while inserting into those other listed tables is not. Is it a coincidence that the ADO.NET data services team chose the Customers table for their quickstart? Maybe, but I doubt it. Regardless, making a non-idempotent insert call from the browser is a bad idea, if you care about Exactly Once.

I’m interested in parsing because I’m interested in Domain Specific Languages. F# is pretty good for internal DSLs, but internal DSLs are obviously limited by the syntax of the host language. If you want complete control over the language, you’ve got to build your own parser.

The defacto standard for parser development is Yet Another Compiler Compiler, or yacc. There’s a version of yacc for .NET as well as one specifically for F#. However, I’m not a fan of yacc. Yacc parsers are specified using context-free grammar (aka CFG). But CFG’s can be ambiguous – actually, it’s nearly impossible to build an unambiguous CFG. Personally, I’m a big fan of Parsing Expression Grammars (or PEGs) which among other advantages makes it impossible to develop ambiguous grammars. Furthermore, PEGs don’t require a separate lexical analyzer like lex, so I think they’re more suitable for building modular compilers.

Since I like PEGs and F# so much, I developed a parser for the PEG grammar from the original PEG whitepaper using F#. The grammar is much simpler than a language like C#, but with twenty nine grammar productions it’s certainly not trivial. The F# implementation is fairly straightforward backtracking recursive decent parser, which makes it easy to understand even if you’re not a parser guru. It’s also small – around 400 lines of code including comments. But I think the code illustrates both the general value of Functional Programming as well as the specific value of F#. Here’s how the series is shaping up (though this is subject to change):

• The Parse Buffer
• Unit Testing
• Syntactical Productions (1)
• Active Patterns
• Syntactical Productions (2)
• Semantic Productions (1)
• The Abstract Syntax Tree
• Semantic Productions (2)
• Recursion and Predicate Functions
• Caching and Tracing
• C# Interop

I was originally planning to post the code for the parser itself with this post. However, i find that I’m revising the code as I write the articles in this series, so I’m going to hold off for now. If you’re really desperate, drop me a line and I’ll see what I can do.

Update: Almost forgot, if you’re going to follow along at home, I’m using the latest version of F#, v1.9.3.7. Note, the F# Downloads page on the MS Research is woefully out of date, so go to the MS Research Downloads page. Currently, it’s the most recent release. It snaps into VS 2005 and 2008 plus has command line tools. If you’re an VS Express user, Douglas Stockwell explained how to roll your own F# Express.

Much Later Update: The code is now available on my Skydrive.

• Short coffee this morning, as I’m home with a tweaked ankle.
• I started playing Indigo Prophecy over the weekend. It’s an original Xbox game, released as part of the new Xbox Originals program. It has a good metacritic score (84), though apparently it wasn’t much of a retail success. I’m enjoying it, though it’s not very challenging. It’s more an interactive movie than a game. Good story, though.
• The ASP.NET MVC preview dropped today, Scott Guthrie has the details. Scott Hanselman has a 40 minute how-to video and Phil Haack has severalarticles up already.
• Speaking of ASP.NET MVC and Scott Guthrie, he’s got another post in his series on ASP.NET MVC. This time, he’s covering how to handle form input / POST data.
• Erik Meijer has posted some of his thoughts on Volta. He’s one of the guys behind Volta, so it’s worth a good look. (via Dare Obasanjo)
• Late Addition – the ASP.NET Extensions is more than just the MVC stuff. It also includes AJAX improvements, Silverlight support, ADO.NET Data Services and ASP.NET Dynamic Data Support. Data Services (formerly Astoria) let’s you easily expose your database via RESTful services. I think Dynamic Data Support used to be code named Jasper. It’s a “rich scaffolding framework” for ASP.NET. I assume that’s to compete w/ Ruby on Rails.

I’m going to start posting about my F# parsing code soon. Obviously, I’ll make the code directly available, but I’m also going to be writing about it quite a bit. Since I’ll be posting lots of F# code snippets, I took the time to build an F# language syntax definition for CodeHTMLer. Of all the various WL Writer Insert Code plug-ins, CodeHTMLer is my favorite because it can be configured not to use <pre> tags, which many RSS readers handle poorly (in my experience).

In case anyone else wants it, I’ve stuck the CodeHTMLer F# language definition up on my SkyDrive. If you using the CodeHTMLer WL Writer Plug-in, you can easily add this to your machine. Once you’ve installed CodeHTMLer and run it once, go to the command line and type cd %appdata%WindowsLiveWriter and you’ll find the LanguageDefinitions.xml file. Edit that file to insert the add the contents of my F# language definition after the <CodeLanguages> tag and you’re all set.

BTW, the first language in the file will be the default language in the plug-in, so if you’re an occasional F# user, you might want to add the F# definition to the end rather than the beginning of the file. If you don’t want to further edit the XML file manually, you can select “Edit Languages” in the plug-in and edit the order of the languages to your heart’s content.

• After using Outlook 2007 as my RSS reader for a few months, I’ve gone back to RSS Bandit. I run two work machines (desktop + laptop) and I finally got tired duplicated blog entries because each copy of Outlook downloads the same post. Also, for some reason Outlook downloads the same Technorati posts over and over again.
• ADO.NET Entity Framework Beta 3 was released. The latest CTP of the EF Tools is also available. And as per the press release, EF has gained support from “Core Lab, DataDirect Technologies, Firebird Foundation Inc., IBM Corp., MySQL AB, Npgsql , OpenLink Software Inc., Phoenix Software International, Sybase Inc. and VistaDB Software Inc”. I’m not sure what that means, exactly, but I guess you’ll be able to LINQ to Entities on a wide variety of DB platforms. Interesting Oracle isn’t on that list. Not really surprising, but interesting.
• Here’s a new ASP.NET MVC article from Scott Guthrie, this one on views and how you pass data to one from a controller. Using generics to get strongly-typed ViewData is pretty sweet. But where’s the MVC CTP that was supposed to be here this week?
• In news about web app tool previews that did ship this week, Live Labs announces Volta. Haven’t installed or played with it yet, but I did read the fundamentals page. It primarily looks like a tool to compile MSIL -> JavaScript, so you can write your code in C# but execute it in the browser. Sam and Jesus are excited, Arnon not so much. Arnon’s argument that being able to postponing architectural decisions is to good to be true is fairly compelling, and not just because he quotes me to support his argument. But I’ll download it and provide further comment after I experiment with it myself.
• Simple Sharing Extensions is now FeedSync. Not sure what else is new about it, other than it’s been blessed with “1.0″ status. The Live FeedSync Dev Center has an introduction, a tutorial and the spec. (via LiveSide)
• Dare likes tuples. Me too. I also like symbols.