#14290: Strictness bug with existential contexts on data constructors -------------------------------------+------------------------------------- Reporter: simonmar | Owner: (none) Type: bug | Status: new Priority: highest | Milestone: 8.2.2 Component: Compiler | Version: 8.2.1 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: | -------------------------------------+------------------------------------- Description changed by simonmar: Old description:
The following:
{{{ {-# LANGUAGE ExistentialQuantification #-} module Main (main) where
main :: IO () main = r `seq` return ()
r :: Rec r = Rec{ a = error "xxx", b = 3, c = True }
class C t instance C Bool
data Rec = forall t. C t => Rec { a :: () , b :: !Int , c :: t } }}}
Should succesed, but fails with `error "xxx"` (but only when compiled with `-O`). The problem is that the strictness signature for the data con wrapper doesn't take into account the dictionary fields.
I have a patch which I'll upload to Phabricator shortly...
New description: The following: {{{ {-# LANGUAGE ExistentialQuantification #-} module Main (main) where main :: IO () main = r `seq` return () r :: Rec r = Rec{ a = error "xxx", b = 3, c = True } class C t instance C Bool data Rec = forall t. C t => Rec { a :: () , b :: !Int , c :: t } }}} Should succeed, but fails with `error "xxx"` (but only when compiled with `-O`). The problem is that the strictness signature for the data con wrapper doesn't take into account the dictionary fields. I have a patch which I'll upload to Phabricator shortly... -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14290#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler