Hi What is the speed of hProjectByLabel/s in Data.HList.Record? . The documentation in hackage http://hackage.haskell.org/packages/archive/HList/latest/doc/html/Data-HList...does not mention it. Perhaps this is because Hlist is designed for supposedly short records and this does not matter too much. looking at the code I guess that everything in HList is O(n) because it uses type-level list structure, but I think that nothing prevents from using a type level balanced tree, Data.Map style, instead. This would permit to implement large heterogeneous Maps with fast access and strongly typed. AFAIK, the alternative is to use a fast data container with data elements encapsulated within Data.Dynamic, that is weakly typed, produces type errors at runtime, which is unsatisfactory and dangerous. Any comments?