On 03.11.12 10:05 AM, Peter Divianszky wrote:
Suppose we have a record update
r { x = f (r x)}
and suppose that most of the time f returns it's argument unchanged.
Recently I've heard about Q-combinators. Central idea: Change (f :: a -> a) to (f' :: a -> Maybe a) returning Nothing when the value didn't change. Then we can replace the record update with smarter code which preserves more sharing.
Just adding a remark here: I actually played with these Q-combinators, they actually worsened performance of Agda. The problem is that they make the code strict. The performance loss due to strictness outweighted the potential performance gain by increased sharing. Q-combinators were developed by John Harrison in the context of ML, which is strict anyway. I guess a compiler support for smart record update would not have the strictness penalty. Cheers, Andreas -- Andreas Abel <>< Du bist der geliebte Mensch. Theoretical Computer Science, University of Munich Oettingenstr. 67, D-80538 Munich, GERMANY andreas.abel@ifi.lmu.de http://www2.tcs.ifi.lmu.de/~abel/