Hi Frank,

I forward this to the Moose list (most PP action is going on there), because other people might be interested as well.

On Wednesday, 20 July 2011, Frank Shearar frank.shearar@gmail.com wrote:

Hi Lukas,

I've been playing around with PetitParser lately (http://www.lshift.net/blog/2011/07/19/un-petit-haskell), and I thought (a) I'd tell you about another happy user and (b) share a trick, which you may already know. A println analogue for debugging one's productions, occasionally useful when one runs too far ahead of one's tests:

PPParser>>debug: aString        ^ self ==> [:x | Transcript showln: ('{1} ({2})' format: {aString. x.}). x].

You might be also be interested in #>=> that passes you a continuation into the block, so it allows you to "debug" before and after the parse. I used it to write the Glamour-based debugger. Look at the tests for more details.

One problem I have found is that PetitStream doesn't work well wrapping a (Squeak) FileStream. I had expected the following to just work:

FileStream        fileNamed: 'myFile'        do: [:f | HaskellParser new parse: f]

but I currently have to read the entire file into a String and parse that. I'm don't know if that's because of a difference between Squeak's and Pharo's FileStream implementation or a problem in PetitParer?

It should work, but convert the stream to a PPStram using #asPetitStream. I cannot verify right now, because I don't have a computer accessible. Parsing directly on a filestream could potentially work (you might need to implement #uncheckedPeek) but will be dead slow (PP extensively uses #position: and #next to randomly acces the stream, as you can see on Figure 2 in http://scg.unibe.ch/archive/papers/Reng10cDynamicGrammars.pdf).

Thanks for sharing your blog post and experience!

Lukas