> And HList paper left me with two questions. The first one is how much > such an encoding costs both in terms of speed and space. And the > second one is can I conveniently define a Storable instance for > hlists. As I said before, I need all this machinery to parse a great > number of serialized nested C structs from a file.
I'm afraid I've overlooked the part about the great serialized C structs. Serializing HList is easy -- it's de-serialization that is difficult. Essentially, we need to write a mini-type-checker. Sometimes, Template Haskell can help, and we can use GHC's own type-checker. Since the approach you outlined relies on Haskell type-classes to express hierarchies, you'll have the same type-checking problem. You'll have to somehow deduce those type-class constraints during the de-serialization, and convince GHC of them. If you assume a fixed number of classes (C struct types), things become simpler. The HList-based solution becomes just as simple if you assume a fixed number of record types. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
