#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 ezyang): Under Simon's algorithm, I don't see why you should have an `O(n * m)` asymptotic behavior. I guess you are trying to handle this case? {{{ type T = Int type S = T type S1 = S type S2 = S -- error message comparing S1 and S2 -- AKA S and S (not Int and Int) }}} Then the problem resolves to this: given two (singly) linked lists which share a common tail, determine the head of the tail. This is a popular coding interview question and you can do better than `O(n * m)`; e.g. by method 3 here http://www.geeksforgeeks.org/write-a-function-to-get-the- intersection-point-of-two-linked-lists/ -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10547#comment:18 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler