#15613: GHCi command, tracing steps of instance resolution for Constraint or expression -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: feature request | Status: new Priority: lowest | Milestone: Component: GHCi | Version: Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #15610 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Iceland_jack):
Plus, remember it's a tree: a goal may lead to multiple sub-goals...
Yes. Should I make a GHC proposal or is it minimal enough to decide here? I started implementing it: Where do I tap into the current machinery and how best to pass the tree back? It took me a while to be able to find the class being solved, by using `mkClassPred clas tys` in definitions like [https://hackage.haskell.org/package/ghc-8.4.3/docs/src/TcInteract.html#runSo... runSolverPipeline], [https://hackage.haskell.org/package/ghc-8.4.3/docs/src/InstEnv.html#memberIn... matchInstEnv] .. {{{#!hs run_pipeline ((stg_name,stg):stgs) (ContinueWith ct) = do { traceTcS ("runStage " ++ stg_name ++ " {") (text "workitem = " <+> ppr ct) ; res <- stg ct ; let current :: PredType current = mkClassPred clas tys ; traceTcS ("end stage " ++ stg_name ++ " }") empty ; run_pipeline stgs res } }}} and then calling `hscTcExpr` from ''UI''. I'm sure there is a better way but that's how I got started -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15613#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler