If you remove the constraint from duplicateDecl, then I get
Redundant constraint: SYB.Data t
In the type signature for:
definingSigsNames :: SYB.Data t =>
[GHC.Name] -> t -> [GHC.LSig GHC.Name]
which is 100% correct: defininingSigssNames doesn’t use its SYB.Data t
constraint
Simon
From: Alan & Kim Zimmerman [mailto:alan.z...@gmail.com]
Sent: 09 January 2015 11:22
To: Simon Peyton Jones
Cc: ghc-devs@haskell.org
Subject: Re: warn-redundant-constraints present as errors
Thanks.
I've found a case where it warns of a redundant constraint, but if I remove the
constraint I get an error saying the constraint is required
--------------------------------------------
import qualified GHC as GHC
import qualified Data.Generics as SYB
duplicateDecl :: (SYB.Data t) => -- **** The constraint being warned against
*******
[GHC.LHsBind GHC.Name] -- ^ The declaration list
->t -- ^ Any signatures are in here
->GHC.Name -- ^ The identifier whose definition is to be
duplicated
->GHC.Name -- ^ The new name (possibly qualified)
->IO [GHC.LHsBind GHC.Name] -- ^ The result
duplicateDecl decls sigs n newFunName
= do
let sspan = undefined
newSpan <- case typeSig of
[] -> return sspan
_ -> do
let Just sspanSig = getSrcSpan typeSig
toksSig <- getToksForSpan sspanSig
let [(GHC.L sspanSig' _)] = typeSig
return sspanSig'
undefined
where
typeSig = definingSigsNames [n] sigs
-- |Find those type signatures for the specified GHC.Names.
definingSigsNames :: (SYB.Data t) =>
[GHC.Name] -- ^ The specified identifiers.
->t -- ^ A collection of declarations.
->[GHC.LSig GHC.Name] -- ^ The result.
definingSigsNames pns ds = def ds
where def = undefined
getSrcSpan = undefined
getToksForSpan = undefined
--------------------------------------------
On Fri, Jan 9, 2015 at 1:08 PM, Simon Peyton Jones
<simo...@microsoft.com<mailto:simo...@microsoft.com>> wrote:
I’ve fixed this
From: Alan & Kim Zimmerman
[mailto:alan.z...@gmail.com<mailto:alan.z...@gmail.com>]
Sent: 08 January 2015 21:46
To: ghc-devs@haskell.org<mailto:ghc-devs@haskell.org>; Simon Peyton Jones
Subject: warn-redundant-constraints present as errors
This is a great feature, here is some feedback
My syntax highlighter in emacs expects warnings to have the word "warning" in
them.
So for the two warnings reported below, the first is highlighted as an error,
and the second as a warning
Language/Haskell/Refact/Utils/TypeUtils.hs:3036:17:
Redundant constraint: SYB.Data t
In the type signature for:
duplicateDecl :: SYB.Data t =>
[GHC.LHsBind GHC.Name]
-> t -> GHC.Name -> GHC.Name -> RefactGhc [GHC.LHsBind
GHC.Name]
Language/Haskell/Refact/Utils/TypeUtils.hs:3045:7: Warning:
Defined but not used: ‘toks
This is in a ghci session, and the file loads without problems, so it is indeed
a warning.
Can we perhaps add the word "Warning" to the output for Redundant constraints?
I also had a situation where it asked me to remove a whole lot of constraints
from different functions, I did them in batches, so did not remove them all
from the file at once, and at some point I had to add at least one of them
back, albeit based on an error message.
Regards
Alan
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