Wednesday, August 16, 2017

Log 081617

Well. I ticked off the items on my to-do list. So, the new one:
  1. Switch over to the standard syntax for 'let'.
  2. Allow for assignment in the REPL.
  3. Maybe allow for object definitions in the REPL.
  4. Support a time-out in the IRC bot.
Another four items. Great!

Tuesday, August 15, 2017

Log 081517

The byte code generation bug turned out to be insignificant but in order to debug it, I changed some code first to trivialize some invariants, then I found the snag.

I fixed some small stuff but didn't find the motivation yet to tick off other parts of the to-do list.

Sunday, August 13, 2017

Log 081317

I implemented a quick-and-dirty IRC bot for Egel, a C++ application which allows for online evaluation. That gave me the opportunity to work on a somewhat neat manner of incorporating the Egel runtime in a C++ application.

It works but not to my satisfaction. I need to change and support two things: 1) Evaluation now works in a cumbersome manner with callbacks which need to go. 2) I need to think about a scheme to call Egel routines from the evaluator. I am not sure what I want here but some tighter integration seems in order.

I also found a not so nice bug in bytecode generation. Well, that's a show stopper. I am not worried since I trust the evaluation scheme I got but annoyed that a bug like that can pop up that late during development. I need to either test a lot or idiot proof it, and it turns out I am not idiotic enough to write down really strange programs which bring all bugs to the surface.

Then there is OO. I think I'll need syntactic sugar for an extend relation. That's not too hard but some work.

So, in order, my small todo list below:
  1. Fix the byte generation bug.
  2. Make calling the evaluator sane.
  3. Add extend relation to objects.
The work is never done.

Friday, August 11, 2017

Log 081117

I implemented a scheme for creating objects but I didn't add a safe scheme yet for destructive assignment.

For the moment I see three different approaches:
  1. Ignore, just let cycles be created. This what I have now.
  2. Detect cycle creation, and fail if a cycle would be created.
  3. Conservatively copy, that part of the tree which holds the cyclic reference is copied.

I am also working a bit on an IRC bot but didn't progress very far yet.

Friday, August 4, 2017

Log 080417

Well. I don't feel like doing much. I registered an account at readthedocs and started thinking a bit about performance. On a small test example, determine the length of a list of a million numbers, the interpreter runs in seventeen seconds whereas the Glasgow Haskell interpreter runs in around a second. 17x slower.

The hotspot is, of course, the bytecode interpreter.

There are a number of things I can do to gain some performance:
  1. Change the register storage from a container to an array.
  2. Fix the amount of copying. (The 'clone' method.)
  3. Expand the bytecode a bit since it's minimal but not fast.
  4. Use multiple inheritance to remove an indirection from arrays of objects.
  5. Write my own reference counting object.
I changed a few lines of code and implemented the first two steps. Performance increased from seventeen to ten seconds on the example.

Wednesday, August 2, 2017


I am thinking of adding a trivial quotation scheme. Nothing difficult, only for combinators. I.e., `x is nothing more than informing the interpreter not to evaluate the combinator x.

I guess I could do it. But is a construct like that useful? I can't get my head around it.

Mike Acton "Data-Oriented Design and C++"