GSoC status report, week 3

Maybe I can get one of these written before the weekly news go up this time... 

My first milestone for haskell-src-exts is to have full and correct support for (almost) everything code-related. When I'm there, I will release haskell-src-exts 1.0.0. And I'm really quite close now.

On the issue of extensions, haskell-src-exts now supports nearly all extensions implemented by GHC. The two exceptions are UnicodeSyntax and NewQualifiedOperators, both of which are considered low priority. Neither should be hard to fix, but other things take precedence currently. There is also ExtensibleRecords, RestrictedTypeSynonyms and HereDocuments, all Hugs extensions, which are not yet supported. These are also considered less important for now.

On the issue of parametrisation, I've had to restructure quite a bit to enable the proper checks for types and contexts. In particular the fact that contexts are parsed as types, and passed in a ctype, means I've had to implement a two-tier check that they are correct. First to check that the type actually represents a valid context, which also transforms it into a list of assertions. Second to check that the assertions are correct in the context they are used. With FlexibleInstances on then anything goes, but without it there's a difference between contexts in class and instance declarations compared to elsewhere. This two-tier system is now in place, and seems to work just fine. In the process, it also gets rid of the wart that was the TyPred constructor in the Type data type, just like I previously got rid of e.g. Wildcard in the Exp data type. I'll probably write a separate entry about this stuff.

I've also improved the interface a lot, with multiple entry points to the parser and some tidying up of the top-level functions. In particular, parseFile now looks at the LANGUAGE pragmas to see what extensions to look for while parsing the rest.

So what remains for 1.0.0? Two things basically. First there are a few bugs in the trac left to squash, which (with one ugly but uncommon exception) shouldn't be much work. Second, there's that issue of handling operator fixities. That shouldn't be a lot of work either, so I have good hopes of having a release candidate out some time early next week. Stay tuned!