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Description
While trying to compile bower-json-0.7.0.0
with current bos/master
: I get an error:
bower-json/src/Web/Bower/PackageMeta/Internal.hs:318:26:
Overlapping instances for Aeson.ToJSON [a]
arising from a use of ‘.=’
Matching instances:
instance [overlappable] Aeson.ToJSON a => Aeson.ToJSON [a]
-- Defined in ‘aeson-0.11.0.0:Data.Aeson.Types.Instances’
instance Aeson.ToJSON [Char]
-- Defined in ‘aeson-0.11.0.0:Data.Aeson.Types.Instances’
Used stack.yaml
:
resolver: lts-5.1
packages:
- '.'
- location:
git: git@github.com:bos/aeson.git
commit: fdb867286b6b4fd5afc703718b0a30dadc300db2
extra-deps:
- fail-4.9.0.0
It compiles fine with aeson
versions in LTS-4.2
and LTS-5.1
though. I have no idea what happened lately in master.
Anyway, my proposal is to remove overlapping FromJSON
and ToJSON
instances, by the same trick as with Read
and Show
, i.e. introducing parseJSONList
and listToJSON
functions. They would have default implementations, so this is not breaking change. With #349 fixed, there won't be other overlapping instances.
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