Re: Typechecker plugins: request for review and another workflow question

On Nov 14, 2014, at 09:14, Adam Gundry wrote:

Thanks, Simon! I've been convinced that TcS is more than we need, and I think the right thing to do is to (optionally) invoke the plugin after the constraints have been unflattened anyway. I've just pushed a commit to wip/tc-plugins-amg that does this. Iavor, Eric, your views on how convenient this alternative is would be most welcome. I'm also wondering if the plugin should be told how many times it has been called, to make it easier to prevent infinite loops.

Thanks, I was just sitting down to figure out how to call the plugins with the unflattened constraints. Is there really a point though in calling the plugins with flattened and unflattened versions of the same constraints? Perhaps we should just settle on one or the other? I think Iavor and I are fine with only passing unflattened constraints to the plugins. It means a bit more work for the type-nat plugin, but shouldn't be a huge issue (I'll confirm this before next week). I don't think the plugins should be told how often they're being called, I'd prefer for GHC to track that and break the loop, if anything. I'm generally unconvinced that tracking the invocations is necessary at all though. The only way I can see an infinite loop occurring is if the plugins keep emitting *new* facts. Disregarding the possibility of a malicious plugin, that should mean that we're making progress towards a solution, right? Eric