#11760: runST with lazy blackholing breaks referential transparency -------------------------------------+------------------------------------- Reporter: Yuras | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect result | Unknown/Multiple at runtime | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by Yuras): * failure: None/Unknown => Incorrect result at runtime Comment: Yes, I agree that it is specific to lazy `ST`. Strict one serializes access to mutable refs, and entering the thunk twice just creates a fresh set on refs. Re performance in presence of `noDuplicate#`: I don't have a use case for lazy `ST` actually, I just found the snippet on twitter. But it looks like lazy `ST` is useless because of the issue, so probably trading performance for correctness makes sense here. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11760#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler