#5499: Tagging constructors with record/product phantom type
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Reporter: basvandijk | Owner:
Type: feature request | Status: closed
Priority: normal | Milestone:
Component: libraries (other) | Version: 7.2.1
Resolution: wontfix | Keywords:
Testcase: | Blockedby:
Difficulty: | Os: Unknown/Multiple
Blocking: | Architecture: Unknown/Multiple
Failure: None/Unknown |
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Changes (by basvandijk):
* status: new => closed
* resolution: => wontfix
Comment:
I
[https://github.com/basvandijk/aeson/commit/4ee946745573ad4a6da2416e612cd4b94929d36c
solved it] using both Pedro's `IsRecord` type-level predicate and the
technique from Simon and Oleg for
[http://www.haskell.org/haskellwiki/GHC/AdvancedOverlap choosing an
instance based on a context].
Although the solution requires some advanced techniques and some extra
language extensions, I'm happy about it. I also managed to keep the change
local (only the instance for constructors has changed).
A tag on [http://www.haskell.org/ghc/docs/latest/html/libraries/ghc-
prim-0.2.0.0/GHC-Generics.html#t:C C] would make all of this a lot easier
and doesn't require as much type-level computation. But it would mean
changing GHC which may not be worth it. So I'm closing the ticket as
`wontfix`.
Pedro and Simon, much thanks for your help!
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5499#comment:9>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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