David Frech wrote:
I'm curious. Can you be more specific about what you thought wanted/needed changing in nhc98's VM and/or compiler?
Well there were a number of issues: - nhc98's existing VM had a very substantial bug because it was originally designed to use the top bit of an address to store information the VM doesn't work on any system that allocates memory in the high-mem area (which is quite common now days). This was built into the runtime pretty deeply. - nhc98's bytecode worked by writing a C file that contained an array with all the bytes in it. i.e. unsigned char bytecodes[] = { ... }; This was used to get linking for free but has several disadvantages. Most of all it ensures that while the bytecode is in theory portable the binaries that nhc produces aren't. - nhc98's runtime is written in a less than obvious way. Rewriting it quite substantially reduced the size, and increased the readability of the code. - the bytecode itself could be very much simplified. The original nhc98 bytecode had instructions for directly manipulating both stack and heap. Yhc simplifies this by moving all the work to be on the stack and then having simple instructions to build heap nodes using data on the stack. This gives quite a substantial reduction in the number of instructions needed to do something. - Reducing the number of instructions, so leaving more space for specialised versions of simple instructions (e.g. a PUSH_1 instructions rather than PUSH, 1), this means almost all instructions fit in a single byte, improving performance.
I haven't played around with nhc98 yet, but I was intrigued by its small size and its (modestly-sized and simple) bytecoded implementation. Should I now be more interested in Yhc instead? ;-)
Well things are still in an early stages of development but it could certainly be worth considering :-)
I'd like to build a web-publishing framework in Haskell that is totally self-contained, very portable, and easy to bootstrap ... and nhc98 or Yhc might be a nice place to start.
That's the idea ;-)
Are you documenting your thoughts about the Yhc implementation somewhere?
There's the blog, the wiki and the webpage (all mentioned in an earlier post). We're in a period of documenting things. The implementation is not ideally documented at the moment but that's something I hope to fix soon. Thanks Tom