[Haskell-cafe] Has anyone looked into adding subtyping to Haskell?

[Stefan Holdermans]

Al,

> Has there been any work on extending Haskell's type system with  
> structural subtyping?

   Koji Kagawaga. Polymorphic variants in Haskell. In Andres Loeh,  
editor, Proceedings of the 2006 ACM SIGPLAN Workshop on Haskell,  
Portland, Oregon, USA, September 17, 2006, pages 37--47. ACM Press,  
2006. [1]

> What is the canonical solution to the expression problem in Haskell?

Not canonical but Loeh and Hinze have proposed open data types:

   Andres Loeh and Ralf Hinze. Open data types and open functions. In  
Annalisa Bossi and Michael J. Maher, editors, Proceedings of the 8th  
International ACM SIGPLAN Conference on Principles and Practice of  
Declarative Programming, July 10--12, 2006, Venice, Italy, pages  
133--144. ACM Press, 2006. [2]

Cheers,

   Stefan

[1] http://portal.acm.org/citation.cfm? 
id=1159842.1159848&coll=ACM&dl=ACM&type=series&idx=1159842&part=Proceedi 
ngs&WantType=Proceedings&title=Haskell&CFID=24140934&CFTOKEN=52915302

[2] http://portal.acm.org/citation.cfm? 
id=1140335.1140352&coll=ACM&dl=ACM&type=series&idx=1140335&part=Proceedi 
ngs&WantType=Proceedings&title=International%20Conference%20on% 
20Principles%20and%20Practice%20of%20Declarative% 
20Programming&CFID=24141725&CFTOKEN=61657761