#11383: CAFs lose sharing due to implicit call stacks -------------------------------------+------------------------------------- Reporter: simonmar | Owner: gridaphobe Type: bug | Status: new Priority: normal | Milestone: 8.0.1 Component: Compiler | Version: 8.0.1-rc1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #11298 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by gridaphobe): * related: => #11298 Comment: As you said, this is really just the monomorphism restriction (or in this case the lack thereof) at work. The two pieces that contribute to this behavior are: 1. `error` is now overloaded with an implicit parameter, the call-stack. 2. GHC infers implicit parameters (including call-stacks) as needed, unless there's an explicit signature or the monomorphism restriction applies. There's a similar report in #11298, see the two definitions of `fooHelper`. We could avoid this (potentially confusing) behavior for the most part by not inferring call-stacks for top-level definitions. I'm a bit reluctant to do so because it makes call-stacks less like implicit parameters, and would require another special case in the type-checker. One of the things I like about the current version of the call-stack solver is how similar implicit call-stacks are to regular implicit parameters. --- I'm actually more concerned about the fact that `-ffull-laziness` changes the behavior. Does this mean we're caching the first call-stack? That would be completely wrong; it would be wrong for any implicit parameter. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11383#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler