#14176: sortOn with tuple of >= 9 Maybe's triggers ghc: panic! with "Simplifier ticks exhausted" -------------------------------------+------------------------------------- Reporter: kostmo | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Given the following code (full Stack project attached): {{{#!haskell module Foo where import Data.List data MyRecord = MyRecord { f1 :: Maybe String , f2 :: Maybe String , f3 :: Maybe String , f4 :: Maybe String , f5 :: Maybe String , f6 :: Maybe String , f7 :: Maybe String , f8 :: Maybe String , f9 :: Maybe String , f10 :: Maybe String , f11 :: Maybe String , f12 :: Maybe String } getComparisonValue x = ( f1 x , f2 x , f3 x , f4 x , f5 x , f6 x , f7 x , f8 x , f9 x ) doSort = sortOn getComparisonValue }}} The following error results: {{{ $ stack build ghc-bug-0.0.0: build (lib) Preprocessing library ghc-bug-0.0.0... [1 of 1] Compiling Foo ( Foo.hs, .stack-work/dist/x86_64 -linux-nopie/Cabal-1.24.2.0/build/Foo.o ) ghc: panic! (the 'impossible' happened) (GHC version 8.0.2 for x86_64-unknown-linux): Simplifier ticks exhausted When trying UnfoldingDone $j_s72t 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: 324566 Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug -- While building package ghc-bug-0.0.0 using: /home/kostmo/.stack/setup-exe-cache/x86_64-linux-nopie/Cabal- simple_mPHDZzAJ_1.24.2.0_ghc-8.0.2 --builddir=.stack-work/dist/x86_64 -linux-nopie/Cabal-1.24.2.0 build lib:ghc-bug --ghc-options " -ddump-hi -ddump-to-file" Process exited with code: ExitFailure 1 }}} Generating a tuple from elements of an object for the purpose of sorting is an idiom I have used in Python at times. The original use case in Haskell for me was excluding some fields of the record in the comparison (e.g. `f10`, `f11`, `f12` fields), rather than using a simple `sort` with `deriving Ord` on `MyRecord`. I worked around the issue for now by blanking out the record fields I with to ignore, instead of re-instantiating a tuple of field values: {{{#!haskell getComparisonValue x = x { f10 = Nothing , f11 = Nothing , f12 = Nothing } }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14176 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler