#15182: Lazier Semigroup instance for Maybe -------------------------------------+------------------------------------- Reporter: andrewthad | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.2.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by oerjan): * cc: oerjan (added) Comment: The last version is ''not'' equivalent - it doesn't produce `Just` until the right argument has been evaluated. For example, with the former, I think `foldMap (Just . (:[])) [1..] = Just [1..]`, but with the latter (and with the current one) it diverges. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15182#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler