#12215: Debugging herald should be printed before forcing SDoc -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: task | Status: new Priority: low | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- When I am debugging panics or infinite loops related laziness issues (e.g., lazy interface checking), I've noticed that sometimes a debugging trace can change the strictness of a function, causing us to tag a thunk too early. Unfortunately, GHC makes it a bit difficult to tell that it's the debug trace's fault. Specifically, if the bad trace has the form `traceTc "foo" someBadSDoc`, we attempt to evaluate `someBadSDoc` before we start printing any output. That's too bad: we should FIRST output `foo`, and then force and print the rest of the SDoc. Internally, `traceTc`'s herald is implemented by catting the herald into the SDoc, so I am not sure what the best way of getting things to be lazier is. I don't think SDoc can be made to stream, so we might have to do something a little nasty like split the trace into two internal trace calls. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12215 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler