#12921: initTc: unsolved constraints -------------------------------------+------------------------------------- Reporter: jlp | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 8.0.1 checker) | Resolution: | Keywords: Operating System: MacOS X | Architecture: x86_64 Type of failure: Compile-time | (amd64) crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): I've trimmed the code down to just this: {{{#!hs {-# LANGUAGE OverloadedStrings #-} module LuaParser (stat) where data Parser a data Stat {-# ANN module "HLint: ignore Reduce duplication" #-} stat :: Parser Stat stat = choice [] }}} This triggers this panic on GHC 8.0.2 and HEAD: {{{ $ /opt/ghc/8.0.2/bin/ghci Bug.hs GHCi, version 8.0.2: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling LuaParser ( Bug.hs, interpreted ) ghc: panic! (the 'impossible' happened) (GHC version 8.0.2 for x86_64-unknown-linux): initTc: unsolved constraints WC {wc_insol = [W] choice_a13R :: t_a13Q[tau:1] (CHoleCan: choice)} Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} But disturbingly, this panic does //not// occur on GHC 8.0.1, so this is a regression. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12921#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler