Getting error about unused instances during "sh validate"

Alfredo Di Napoli alfredo.dinapoli at
Thu Jun 12 17:30:13 UTC 2014

Hi Simon,

It's strange because I was not getting that before (say 2 weeks ago) and as far as I know I have not changed my build type (always been "quick").
I'll try to see if playing around with -O will change things and report back.



> On 12/giu/2014, at 16:36, Simon Peyton Jones <simonpj at> wrote:
> 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 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:
> Thanks!
> Alfredo
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