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 |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |