Archive for November 2008
MGrammar is a toolset for writing grammars and working with them. The MGrammar grammar description language lets you write what is basically an LALR(1) grammar, which means it’s about as powerful as YACC. Or it would be, if it wasn’t also a GLR parser, which means that when your language is ambiguous you get all the possible alternatives. This is a nice way of avoiding the NP-completeness issues around ambiguity detection.
MGrammar also separates syntax (LALR(1)) from tokenizing (regular). This is a win, since sometimes tokenizing is all you need.
The coolest thing about MGrammar is the grammar development tool. It’s a three-paned window, with sample text on the left, the grammar in the middle, and the parse tree on the right. You can change the sample or the grammar at will, and it reparses with every keystroke. When your grammar finds a parse error or ambiguity in the sample text, the sample text gets a red underline with Intellisense. When your grammar itself has an error in it, you also get a red underline with Intellisense, which is reasonable because there is in fact an MGrammar description of MGrammar itself, which drives the Intellisense.
It works very well in practice and makes grammar writing so much more productive it’s not even funny. Using a lot of negation can make it go nonlinear, but it’s manageable.
On a sad note, Gilad and his merry band have lost their funding. This really sucks, as Newspeak is one of the most interesting language efforts around. I very much hope a community takes root around it and drives it. (If it can happen to Factor, of all things, it can happen to Newspeak.)
And finally, yes, http://robjsoftware.org was broken for the last month or two. I had one email filtering rule for all of GoDaddy, and when we moved to Seattle this spring, the address change broke GoDaddy’s monthly charging, but I didn’t see the warning because it was in the same bucket with all of GoDaddy’s spam^H^H^H^Hinformative emails. Which I never read. Sigh. I clearly need a fully redundant alerting and monitoring system for my blog.