2011-05-10 15:31, Heinrich Apfelmus skrev:
I'm also unhappy about some of the boilerplate. For instance, have a look at the function goE in compileAccumB (line 210), it's just a generic applicative traversal through the data type.
Most likely, this boilerplate could be simplified using syntactic.
Hm, does the boilerplate get removed or only simplified? I was hoping that one could use a completely generic traversal; but is that actually the case?
I was using careful wording :) I think the traversal can be completely generic. But syntactic brings its own (constant) overhead, so I felt the word "remove" might be too strong.
On closer inspection, I'm discovering another issue, namely the need for the Typeable class. This is quite unfortunate, because it would mean that I won't be able to make an API built on type classes like Functor or Applicative. Some discussion on that can be found at the end of
http://apfelmus.nfshost.com/blog/2011/04/24-frp-push-driven-sharing.html
Hm... The only reason (afair) for having Typeable constraints in the tree was that my code motion transform (not yet released) needs to move around nodes in a way that the type checker is not happy with. But as long as my algorithm is correct, the type casts will actually always succeed. So it might be possible to use unsafeCoerce directly and get rid of Typeable. There might also be ways to make Typeable optional... I will look into this.
So, it looks like I can't make use of syntactic at the moment. Then again, my library is probably one of the strongest tests of expressivity for endeavors like syntactic , so that's fine. Another example of similar difficulty would be D. Swierstra's recent parser/grammar combinators that can handle left-recursive grammars. Once syntactic can deal with those, you're the king! :)
Thanks for the tip! It would be interesting to try out these libraries for real, if only for the sake of getting to know the practical limits of syntactic. But my focus is currently on the Feldspar implementation, so I probably won't have time for things like this in a (long) while. / Emil