6 Jun 2012 joolean   » (Journeyer)


I've just thrown together a release of a little project I started during this year's LibrePlanet conference, an implementation of the Apache Thrift framework in R6RS Scheme: r6rs-thrift. I thought it would be a fun, quick hack -- my assumption was that I could lift a lot of the type system and code generation stuff from r6rs-protobuf, my Scheme Protocol Buffers implementation from last year -- but it turned out that Thrift's a bit more complicated. Which is not to say that it wasn't fun to work on. But Thrift includes pluggable wire protocols, parameterized types, and some interesting variations on Protocol Buffers' vanilla structs (unions and exceptions). And there's not a whole lot (read: any) documentation, so I had to pretty much reverse engineer the serialization and codegen semantics by picking through the thriftc source code.

One interesting thing that came out Thrift's type system is that because you can effectively declare a type at the same time you're declaring a field of that type -- via, say, a container type as a field in a struct -- I had to add a layer of indirection to the type resolution system such that a descriptor for a user-defined type is declared (and registered) once and then used via an explicit "type reference" record everywhere else. Type references themselves can be parameterized to support Thrift's "generic" containers. I was initially worried about introducing that construct, but it ended up being reasonably discrete and quite powerful. I'm considering porting it back to r6rs-protobuf, just for, you know, funsies.

I was able to port the builder pattern that Protocol Buffers uses over to this implementation, which I thought was a neat little coup. Thrift is, you know, fine, but the mutability of the data types generated by the official compiler has always irked me, in part because it means there's no validation applied until you're about to marshal something over the wire. I suppose you could mount a philosophical defense to the effect that you don't really need an object to be well-formed until that point, but that presumes an awful lot about how you're planning to use your generated data structures.

At any rate: I made it; go get it.

Latest blog entries     Older blog entries

New Advogato Features

New HTML Parser: The long-awaited libxml2 based HTML parser code is live. It needs further work but already handles most markup better than the original parser.

Keep up with the latest Advogato features by reading the Advogato status blog.

If you're a C programmer with some spare time, take a look at the mod_virgule project page and help us with one of the tasks on the ToDo list!