Extensible data types?

Jose Emilio Labra Gayo labra@pinon.ccu.uniovi.es
Fri, 20 Oct 2000 12:36:39 +0200 (METDST)

> The above code fails to type check due to instances
> overlapping. Hugs gives the following error message:
In Hugs, there is a flag that you can set to allow overlapping instances

	:s +o

In GHC, you can also set


BTW, I use extensible union types in a "Language prototyping System" that
I am implementing and which compiles with GHC and Hugs (it is based
on Liang, Hudak and Jones paper). 
You can download the source code from 

Best regards, Jose Labra