Re: Extensible data types?

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 -fallow-overlapping-instances 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 "http://lsi.uniovi.es/~labra/LPS/LPS.html" Best regards, Jose Labra http://lsi.uniovi.es/~labra