#10547: feature request: expanding type synonyms in error messages -------------------------------------+------------------------------------- Reporter: osa1 | Owner: osa1 Type: feature request | Status: new Priority: low | Milestone: 7.12.1 Component: Compiler (Type | Version: checker) | Keywords: Resolution: | Architecture: Operating System: Unknown/Multiple | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Revisions: D1016 -------------------------------------+------------------------------------- Comment (by simonpj): Ha ha. Yes, ideally so. But in practice I suspect it'll be infeasible to find the maximally-unexpanded version; as your example shows. I'd settle for: * If the head of the application matches (i.e. `T t1` vs `T t2`) then walk down `t1`,`t2`. * Otherwise expand both sides to a non-synonym type constructor. There is room for cleverness here. But a function with the above signature (for `expandSynonymsToMatch`) will serve the purpose, and we could start with a fairly simple one as above. Or do something cleverer if you like. Simon -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10547#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler