id,summary,reporter,owner,description,type,status,priority,milestone,component,version,resolution,keywords,cc,os,architecture,failure,testcase,blockedby,blocking,related,differential,wikipage
8021,Multiple constraint classes - the alternative to superclass,wvv,,"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
}}}
",feature request,closed,normal,,Compiler,7.6.3,invalid,,,Unknown/Multiple,Unknown/Multiple,None/Unknown,,,,,,