#13615: Nondeterminism in ‘pure’ function w/ parallel evaluation & memo combinators -------------------------------------+------------------------------------- Reporter: pacak | Owner: (none) Type: bug | Status: new Priority: highest | Milestone: 8.2.1 Component: Compiler | Version: 8.2.1-rc2 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: | -------------------------------------+------------------------------------- Comment (by pacak): I've confirmed that ghc has an interesting sense of equality: {{{ regroup :: (NFData a, Show a, Hashable a, Eq a, Ord a) => [(a, Int)] -> [(a, Int)] regroup xs = let xs' = HM.toList $ HM.fromListWith (+) xs s' = sum (map snd xs') s = sum (map snd xs) in if s' /= s then if show s' == show s then error "WAT????" else error $ "Those are expected to be equal" ++ show (s', s) else xs' }}} {{{ gamebooksolver-solvebook02: Those are expected to be equal(141,121) CallStack (from HasCallStack): error, called at src/Main.hs:50:26 in main:Main gamebooksolver-solvebook02: Those are expected to be equal(384,300) CallStack (from HasCallStack): error, called at src/Main.hs:50:26 in main:Main gamebooksolver-solvebook02: Those are expected to be equal(1045,1045) CallStack (from HasCallStack): error, called at src/Main.hs:50:26 in main:Main gamebooksolver-solvebook02: WAT???? CallStack (from HasCallStack): error, called at src/Main.hs:49:26 in main:Main gamebooksolver-solvebook02: WAT???? CallStack (from HasCallStack): error, called at src/Main.hs:49:26 in main:Main gamebooksolver-solvebook02: WAT???? CallStack (from HasCallStack): error, called at src/Main.hs:49:26 in main:Main }}} Actually it's even worse, note third error. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13615#comment:16 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler