circular loading

If module m1 requires m2 and m2 requires m1, then I get a StackOverflowError.

Lua has the same problem.

fixed in rev 328.  Now the _ENV of a module is put in Package.loaded before the module is run.  And if there is an error, everything is cleaned up and returned to its prior state.  closing

I changed my mind on this.  Handling circular loading can introduce subtle bugs.  Better to just fail and have the programmer handle this manually.  So I reverted this change.