Does not happen for me. Maybe you are compiling without –O (odd, but possible)? mapMaybeFB is mentioned only inside a RULE, so perhaps it’s regarded as un-referenced without –O? Simon From: ghc-devs [mailto:ghc-devs-bounces@haskell.org] On Behalf Of Alfredo Di Napoli Sent: 12 June 2014 12:31 To: ghc-devs@haskell.org Subject: Getting error about unused instances during "sh validate" Hello guys, am I the only one to get the following when I run "sh validate"? libraries/base/Data/Maybe.hs:139:1: Warning: Defined but not used: ‘mapMaybeFB’ <no location info>: Failing due to -Werror. make[1]: *** [libraries/base/dist-install/doc/html/base/base.haddock] Error 1 make[1]: *** Waiting for unfinished jobs.... make: *** [all] Error 2 I'm working on this ticket, but I can't see how that can be related: https://ghc.haskell.org/trac/ghc/ticket/8226 Thanks! Alfredo