Getting error about unused instances during "sh validate"

Simon Peyton Jones simonpj at
Thu Jun 12 14:36:08 UTC 2014

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?


From: ghc-devs [mailto:ghc-devs-bounces at] On Behalf Of Alfredo Di Napoli
Sent: 12 June 2014 12:31
To: ghc-devs at
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:

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