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
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