#14349: Semigroup/Monoid instances for System.Exit.ExitCode -------------------------------------+------------------------------------- Reporter: neil.mayhew | Owner: (none) Type: feature | Status: new request | Priority: low | Milestone: Component: | Version: 8.2.1 libraries/base | 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: -------------------------------------+------------------------------------- Please add instances for ExitCode along the following lines: {{{#!hs instance Monoid ExitCode where mempty = ExitSuccess mappend ExitSuccess b = b mappend a _ = a }}} This allows the summary result of multiple child processes to be computed naturally. For example: {{{#!hs mconcat <$> mapM system commands }}} The result is `ExitSuccess` if they all succeeded, and the leftmost failure otherwise -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14349 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler