Multiple constraint classes - the alternative to superclass

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

Trac metadata

Trac field	Value
Version	7.6.3
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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