Print exception and break in clang_visitChildren

[phadej]

Exceptions doesn't seem to fly through C-frames, so we need to handle them better.

For now, I just print and break. This makes test-suite not fail with pure exceptions.

It took me whole morning to figure out why throwIO weren't catched.

[phadej]

But we need to think of proper solution, this cannot be even called a band-aid.

[edsko]

I guess the better solution would involve the Haskell function catching the exception and more explicitly returning it to the C function somehow?

[phadej]

For the record https://gist.github.com/phadej/059993b3d430515fd97a3ee6033510c4 is an example: the exception is not caught, if you run that program you get

problem: user error (blargh)

i.e. uncaught exception, even if there is try.

I guess the better solution would involve the Haskell function catching the exception and more explicitly returning it to the C function somehow?

I think the way to solve is to catch exception, store them in a mutable cell, and then make clang_visitChildren throw it after C-call returns. I'll try that next.