#8021: Multiple constraint classes - the alternative to superclass -----------------------------+---------------------------------------------- Reporter: wvv | Owner: Type: feature request | Status: new Priority: normal | Component: Compiler Version: 7.6.3 | Keywords: Os: Unknown/Multiple | Architecture: Unknown/Multiple Failure: None/Unknown | Blockedby: Blocking: | Related: -----------------------------+---------------------------------------------- This is alternative to SuperClasses - multiple constraint Classes Now: {{{ class Monoid a where ... class Monad m => MonadPlus m where ... }}} It could be: {{{ class Monoid a where ... class Monad m => Monoid m where ... class Arrow c => Monoid c where ... foo :: Monad m => Monoid m => m a }}} all classes must have same functions with same kind. And if you wish to write superclass, it would be easy to write {{{ class BeforeNum a where .... class BeforeNum a => Num a where ... foo :: BeforeNum a => Num a => a }}} '''Backward compatibility''' If class have single constraint, you could write without it. If class have many constrains, you could write without it, if it is empty one. {{{ bar :: MonadPlus m => m a <<==>> bar :: Monad m => MonadPlus m => m a foo :: Monoid a => a <<==>> foo :: () => Monoid a => a }}} -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/8021 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler