This makes it possible to define "infinite" instances for any class
#15322: `KnownNat` does not imply `Typeable` any more when used with plugin -------------------------------------+------------------------------------- Reporter: chshersh | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 Resolution: | Keywords: | typeable,knownnat Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: #10348 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): like this: Well, how does the `KnownNat` constraint help in defining the instance for `MyClass (T n)`? Presumably, because `KnownNat` lets you use `natSign`: {{{ class KnownNat (n :: Nat) where natSing :: SNat n }}} If that's what you need for `instance MyClass (T n)`, then that makes perfect sense. But it makes no such sense for `Typeable`. How does having `KnownNat n` available help you write the `Typeable` instance? I think we just need built-in behaviour for `Typeable (n :: Nat)`, without any reference to `KnownNat`, don't we? There is ''some'' such built-in behaviour already, but I don't understand what it is, and it's clearly dodgy as this ticket shows. Would you like to elaborate your description of what happens now? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15322#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler