Mirah Office Hours: After the hiatus

Lower Falls of the Yellowstone
I took last week off, I was a little busy vacationing and all. I had a very nice time and enjoyed not having internet or cell service. But this last Sunday I was back at it, hacking away on Mirah.

Getting Started

I started by pulling latest, because there had been some changes since the last time I checked out Mirah. Immediately I went from having 2 test failures to having 200 some errors with the message NativeException: java.lang.ClassNotFoundException: mirah.impl.Map$Extension4.

This had something to do with the bootstrap jar being upgraded, but I wasn’t sure what.
I tried updating my local Java from 1.6.0_22 to 1.6.0_24, that didn’t work–but it changed the error to RuntimeError: Compilation error.

I also ran rake clean and rake clobber and poked around for other stale files. It was weird because if I checked out the jar from before the change everything worked again.

Finally, I tried making a fresh clone of the repo and that worked–which I found a little strange. My suspicion is that somewhere I missed some build files that were screwing things up on the path, but I’m really not sure.

Somewhere in there I also blew away my rvm JRuby install and reinstalled it. When I did that, I also chmoded .rvm/hooks/after_use_jruby so nailgun wouldn’t cause issues like it did before.

Actually doing stuff

I looked at pull request #95, and couldn’t reproduce the issue it solved, so I left a comment to that effect.

On StackOverflow, I answered a question about Mirah’s metaprogramming support. I think I should work up a page like that to put in the wiki, so there is a canonical place to look for macro and metaprogramming information.

test reorg continues
I finished teasing apart the bytecode and javac jvm tests. Now, they run the same suite but use different helpers instead of sharing through subclassing. This means we can start to break apart the big test_jvm_compiler.rb file(2876 lines!) into more focused test files, which I think will be a big win for helping new people find a place to put new tests.

The only problem with the current implementation is that the rake test task is dependent on the sub tasks instead of calling them inside itself. This is a problem because the task stops at the last suite to fail, instead of doing like Rails does and running them all and telling you error in test:units or whatever.

I continued poking at the main method thing I’ve been working on, and managed to completely hose the test suite–clearly I’m doing something wrong somewhere. So I think I’ll take another crack at it next weekend. I think I was trying too hard to decompose the compile helper methods, rather than getting it working and then decomposing it.

Scoping Thoughts

I read the scoping discussion about macro scoping and formed an opinion about it.

The discussion boils down to how to handle scoping within macros. For macros to be useful, you need to be able to refer to variables from the outer scope. The problem is that just dropping the code the macro generates into the outer scope can be problematic when the code the macro generates has its own variables. Hmm, that explanation wasn’t great–how ’bout an example:

Here, if we use the outer scope without making temporary variables for the variables in the macro, we’ll get as output 4, which is probably not what we expected.

My Scoped Opinion

My thought is that anything assigned/declared to in the quote block in a macro should be turned into a variable local to the macro–eg foo’s bar becomes bar_1, or something. But, unquoted elements within the quote should use the outer scoping and not create temporary variables, so that when the macro is put in place, the function baz looks like:

That gets you the ability to reference things outside the macro, letting you manipulate them within it, but does not bleed temporary variables from the macro into the outer scope. Now, how to implement that, I don’t really have a good idea. An exercise for the reader.

I think it was a pretty productive four hours. See you next week!

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