#10547: feature request: expanding type synonyms in error messages -------------------------------------+------------------------------------- Reporter: osa1 | Owner: Type: feature request | Status: new Priority: low | Milestone: 8.0.1 Component: Compiler (Type | Version: checker) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: | typecheck/should_fail/ExpandSynsFail1,2,3,4 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1016, Wiki Page: | Phab:D2198 -------------------------------------+------------------------------------- Comment (by osa1): OK, this should be fixed now. I'm currently validating the patch locally. As for why not enable this by default: The algorithm is looking through all expansions, so if the first type can be expanded `n` and second type `m` times, it takes `O(n * m)` steps to find a version of the error message that has minimum amount of expansions. When fixing this bug I realized that type synonym expansion is probably fast enough, and in practice `n` and `m` will not be too big, so maybe it's OK to enable this by default. We should probably just generate some pathological cases and look at compile times with and without `-fprint-expanded-synonyms`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10547#comment:17 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler