#10845: Incorrect behavior when let binding implicit CallStack object -------------------------------------+------------------------------------- Reporter: nitromaster101 | Owner: gridaphobe Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.11 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #10846 | Differential Rev(s): Phab:D1422 Wiki Page: | -------------------------------------+------------------------------------- Comment (by gridaphobe): If I understand your suggestion correctly, this won't fix my example. Why? Because `?loc` creates an `IPOccOrigin` constraint, which you suggest we should freely solve from other call-stack constraints (I take this to mean the usual form of solving an IP, ie we don't push on the stack). So the two `?loc` constraints would be consolidated to one, which we would default to the empty stack. But perhaps this isn't so bad after all. My example was a bit of a red herring, what we really care about is that in {{{ f :: (?stk :: CallStack) => .. main = print (f 0) >> print (f 1) }}} the two calls to `f` are not consolidated to a single constraint. `f x` gives rise to an `OccurrenceOf` constraint, which you suggest we would solve by pushing on the stack and emitting an `IPOccOrigin` constraint, so we '''would''' get the correct behavior here. So, I think under your suggestion, we'll never see a `?loc` in the call- stack, but I think that's fine. (It always stuck me as a bit odd to have the root of the call-stack be an occurrence of an IP, rather than a function call) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10845#comment:14 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler