#11700: pattern match bug -------------------------------------+------------------------------------- Reporter: TobyGoodwin | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: | https://github.com/TobyGoodwin/odd- | ghc-pattern-bug Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by thomie): Here is a reproducer: {{{#!hs {-# LANGUAGE ExistentialQuantification #-} {-# LANGUAGE TypeFamilies #-} -- Remove this line and the code compiles. module T11700 where data Muse data Message data Folder class PersistEntity record data Entity record = PersistEntity record => Entity record fn1 :: (Entity Muse, Entity Message, Entity Folder) -> (Message, Folder) fn1 cluster = let (Entity muse, Entity msg, Entity fldr) = cluster in (msg, fldr) }}} {{{ [1 of 1] Compiling T11700 ( T11700.hs, /tmp/T11700.o ) T11700.hs:17:12: error: • Couldn't match expected type ‘Folder’ with actual type ‘Folder’ • In the expression: fldr In the expression: (msg, fldr) In the expression: let (Entity muse, Entity msg, Entity fldr) = cluster in (msg, fldr) T11700.hs:17:7: error: • Couldn't match expected type ‘Message’ with actual type ‘Message’ • In the expression: msg In the expression: (msg, fldr) In the expression: let (Entity muse, Entity msg, Entity fldr) = cluster in (msg, fldr) }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11700#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler