Attribute Grammars in Bison

[Mihai Calin Ghete]

Hello,

For mymaster's thesis project at the Vienna University of Technology I 
am adding attribute grammar support to Flex and Bison. Bison already 
supports semantic actions which are executed during a shift / reduce; 
the thesisadds the ability to define multipleattributes per symbol and 
rules to calculate each attribute in part, including dependencies 
onattributes of the parent or of child nodes. Attributes are calculated 
as early as possible, but if an attribute depends on another that has 
not been calculated yet, it is enqueued until calculation becomes possible.

These changes are inspired by Ox, a pre-processor for lex/yacc with 
largely the same feature set and similar syntax( 
https://compilers.iecc.com/comparch/article/93-11-100). Ox is currently 
used together with Flex/Bison to teach the concept of attribute grammars 
in the compiler construction course at Vienna UT. Work on Ox does not 
appear to have continued since the 1.04 release in 1994 and Ox itself is 
not Free software, although the source is available and the program is 
free to use, see https://www.complang.tuwien.ac.at/ubvl/ox/.

The chosen approach is to build a dependency graph at runtime (during 
each reduce operation) and evaluate each attribute as soon as all of its 
dependencies are resolved. This procedure is relatively simple but 
effective. The evaluator targets the LALR ("yacc.c") and GLR C skeletons.

Would it be of interest to have such functionality as part of mainline 
Bison?

Kind regards,
Mihai