#7624: Handling ImplicitParams in Instance Declaration
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Reporter: philipjf | Owner:
Type: bug | Status: new
Priority: normal | Milestone: 7.8.1
Component: Documentation | Version: 7.6.1
Resolution: | Keywords: ImplicitParams
Operating System: Unknown/Multiple | Architecture: Unknown/Multiple
Type of failure: Documentation bug | Difficulty: Unknown
Test Case: | Blocked By:
Blocking: | Related Tickets:
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Description changed by simonpj:
Old description:
> The GHC documentation states that ImplicitParam's may not be used in
> class or instance declaration constraints. see for example
> http://www.haskell.org/ghc/docs/7.6.1/html/users_guide/other-type-
> extensions.html In practice though, at least on the Mac, all recent
> version of GHC have permitted such instances. At the very least the
> documentation should make clear that the compiler might permit such
> instances, but they have undefined behaviour. Ideally, these would
> simply be permitted.
>
> [http://joyoftypes.blogspot.com/2013/01/using-compiler-bugs-for-fun-and-
> profit.html Why I think the (undocumented) current behavior is correct]
New description:
The GHC documentation states that `ImplicitParam`'s may not be used in
class or instance declaration constraints. see for example
http://www.haskell.org/ghc/docs/7.6.1/html/users_guide/other-type-
extensions.html In practice though, at least on the Mac, all recent
version of GHC have permitted such instances. At the very least the
documentation should make clear that the compiler might permit such
instances, but they have undefined behaviour. Ideally, these would simply
be permitted.
[http://joyoftypes.blogspot.com/2013/01/using-compiler-bugs-for-fun-and-
profit.html Why I think the (undocumented) current behavior is correct]
[[BR]]
[http://www.reddit.com/r/haskell/comments/178w9u/using_compiler_bugs_for_fun_and_profit/
reddit discussion thereof]
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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7624#comment:4>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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