[Haskell-cafe] More Language.C work for Google's Summer of Code

Edward Amsden eca7215 at cs.rit.edu
Tue Mar 30 16:46:01 EDT 2010

I'd be very much interested in working on this library for GSoC. I'm
currently working on an idea for another project, but I'm not certain
how widely beneficial it would be. The preprocessor and
pretty-printing projects sound especially intriguing.

On Tue, Mar 30, 2010 at 1:30 PM, Aaron Tomb <atomb at galois.com> wrote:
> Hello,
> I'm wondering whether there's anyone on the list with an interest in doing
> additional work on the Language.C library for the Summer of Code. There are
> a few enhancements that I'd be very interested seeing, and I'd love be a
> mentor for such a project if there's a student interested in working on
> them.
> The first is to integrate preprocessing into the library. Currently, the
> library calls out to GCC to preprocess source files before parsing them.
> This has some unfortunate consequences, however, because comments and macro
> information are lost. A number of program analyses could benefit from
> metadata encoded in comments, because C doesn't have any sort of formal
> annotation mechanism, but in the current state we have to resort to ugly
> hacks (at best) to get at the contents of comments. Also, effective
> diagnostic messages need to be closely tied to original source code. In the
> presence of pre-processed macros, column number information is unreliable,
> so it can be difficult to describe to a user exactly what portion of a
> program a particular analysis refers to. An integrated preprocessor could
> retain comments and remember information about macros, eliminating both of
> these problems.
> The second possible project is to create a nicer interface for traversals
> over Language.C ASTs. Currently, the symbol table is built to include only
> information about global declarations and those other declarations currently
> in scope. Therefore, when performing multiple traversals over an AST, each
> traversal must re-analyze all global declarations and the entire AST of the
> function of interest. A better solution might be to build a traversal that
> creates a single symbol table describing all declarations in a translation
> unit (including function- and block-scoped variables), for easy reference
> during further traversals. It may also be valuable to have this traversal
> produce a slightly-simplified AST in the process. I'm not thinking of
> anything as radical as the simplifications performed by something like CIL,
> however. It might simply be enough to transform variable references into a
> form suitable for easy lookup in a complete symbol table like I've just
> described. Other simple transformations such as making all implicit casts
> explicit, or normalizing compound initializers, could also be good.
> A third possibility, which would probably depend on the integrated
> preprocessor, would be to create an exact pretty-printer. That is, a
> pretty-printing function such that pretty . parse is the identity.
> Currently, parse . pretty should be the identity, but it's not true the
> other way around. An exact pretty-printer would be very useful in creating
> rich presentations of C source code --- think LXR on steroids.
> If you're interested in any combination of these, or anything similar, let
> me know. The deadline is approaching quickly, but I'd be happy to work
> together with a student to flesh any of these out into a full proposal.
> Thanks,
> Aaron
> --
> Aaron Tomb
> Galois, Inc. (http://www.galois.com)
> atomb at galois.com
> Phone: (503) 808-7206
> Fax: (503) 350-0833
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