[GHC] #8643: Silent name shadowing

[GHC]

#8643: Silent name shadowing
------------------------------------+-------------------------------------
       Reporter:  mirpa             |             Owner:
           Type:  feature request   |            Status:  new
       Priority:  normal            |         Milestone:
      Component:  Compiler          |           Version:  7.4.1
       Keywords:                    |  Operating System:  Unknown/Multiple
   Architecture:  Unknown/Multiple  |   Type of failure:  None/Unknown
     Difficulty:  Unknown           |         Test Case:
     Blocked By:                    |          Blocking:
Related Tickets:  #5288             |
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 I have code like:
 {{{
 let baseTex =
   (getTexPropNode nodes . NC.properties . NC.av $ geometry)
   >>= baseTex
   >>= (flip Map.lookup texs) . NC.tdSource
 }}}
 which gives me error:
 {{{
 Games/secunda/Graph.hs:224:23:
     Couldn't match expected type `TexProperty -> Maybe a0'
                 with actual type `Maybe b0'
     In the second argument of `(>>=)', namely `baseTex'
     In the first argument of `(>>=)', namely
       `(getTexPropNode nodes . NC.properties . NC.av $ geometry)
        >>= baseTex'
     In the expression:
       (getTexPropNode nodes . NC.properties . NC.av $ geometry)
       >>= baseTex
       >>= (flip Map.lookup texs) . NC.tdSource
 }}}

 However if I try to get type of expressin on the right hand side of {{{let
 baseTex = ...}}} in ghci then I get no error. Problem is that I am
 importing module with function {{{baseTex :: TexProperty -> Maybe
 TexDesc}}} and that function is shadowed by {{{let}}} expression which
 should have type of {{{Maybe Texture}}}.

 I tried to use {{{ghc-options: -Wall -fwarn-name-shadowing}}} in Cabal
 with no effect.

 From above error I conclude, that I made a type error. So I try to get
 type of expression in ghci which results in correct type - that makes my
 confusion. While I am trying to concentrate on type error, I am missing
 that I shadowed function by variable.

 This is not for the first time I've done same mistake. I would appreciate
 to get warnings about name shadowing since they makes me belief that I am
 using names of different type.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8643>
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