#7642: Nullary type classes ----------------------------------------+----------------------------------- Reporter: shachaf | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler (Type checker) | Version: 7.6.1 Keywords: | Os: Unknown/Multiple Architecture: Unknown/Multiple | Failure: None/Unknown Difficulty: Unknown | Testcase: Blockedby: | Blocking: Related: | ----------------------------------------+----------------------------------- Comment(by DerekElkins): The idea is that there wouldn't necessarily be an instance. The final application code would make the instance, in that case, if they were willing to rely on results that rely on the truth of the Riemann Hypothesis. Similarly for Unsafe. Until that instance was made, it would be a compile error (an unresolvable constraint), so you'd be notified if you inadvertently relied on it, and it would be explicit in the signatures of all functions that used the features. Another use-case is statically configurable parameters, e.g. class Modulus where modulus :: Integer. With this, applications can configure such parameters just by specifying some instances, say in their Main module. -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/7642#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler