Reform of the Monad, and Disruptive Change

Malcolm Wallace malcolm.wallace at
Fri Feb 4 11:08:15 CET 2011

On 4 Feb 2011, at 09:41, John Smith wrote:

> There has been a fair amount of discussion, both on this list and  
> libraries, regarding the Monad class hierarchy. The many on the  
> libraries list expressed support for the patch at 
> , conditional on it being part of the next Haskell report. However,  
> Haskell' prefers patches to have been implemented before proposing  
> here.
> What is the best way out of this deadlock?

I suggested, and several people +1'd, that if we are making disruptive  
changes to the standard libraries defined in the Language Report  
(especially the Prelude), then we should aim to make a thorough job of  
cleaning up all the cruft and redesigning in a single strike.  This  
means not just rearranging the Monad hierarchy, but looking at I/O  
types, exceptions, the default strictness of foldl, and much much  
more.  I would expect the language committee to get involved in  
reviewing the decisions of the base library strike force.

Then (for instance) ghc could make a major release with the refreshed  
libraries, and after a little experience in the field (and perhaps a  
few patches), the libraries would then proceed to be blessed as part  
of the subsequent language standard.


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