#10105: ghc panic Simplifier ticks exhausted when trying UnfoldingDone x_alB -------------------------------------+------------------------------------- Reporter: | Owner: dramforever | Status: new Type: bug | Milestone: Priority: normal | Version: 7.10.1-rc2 Component: Compiler | Operating System: Unknown/Multiple Keywords: | Type of failure: None/Unknown Architecture: | Blocked By: Unknown/Multiple | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- The following code causes a panic. It's the Y combinator. {{{#!hs module Y where newtype F a = F { unF :: F a -> a } y :: (a -> a) -> a y = \f -> (\x -> x (F x)) (\x -> f (unF x x)) }}} {{{ bash$ ~/src/ghc-7.10.0.20150123/installed/bin/ghc -c Y.hs ghc: panic! (the 'impossible' happened) (GHC version 7.10.0.20150123 for x86_64-unknown-linux): Simplifier ticks exhausted When trying UnfoldingDone x_alB To increase the limit, use -fsimpl-tick-factor=N (default 100) If you need to do this, let GHC HQ know, and what factor you needed To see detailed counts use -ddump-simpl-stats Total ticks: 4722 Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} However it works fine in GHCi {{{ bash$ ~/src/ghc-7.10.0.20150123/installed/bin/ghci Y.hs GHCi, version 7.10.0.20150123: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Y ( Y.hs, interpreted ) Ok, modules loaded: Y. *Y> take 10 (y (1:)) [1,1,1,1,1,1,1,1,1,1] }}} I have tried this code with 7.6.3, 7.8.3 and 7.10.1-rc2. Same result. At least in 7.10.1-rc2 it doesn't work even with -fsimpl-tick- factor=100000 (that's 10^5^) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10105 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler