GHC & Extensible Records
From the GHC FAQ:
I have a hunch that extensible records are going to be a condition of bringing functional programming to the masses. I need to learn why they are hard.Does GHC implement any kind of extensible records?
No, extensible records are not implemented in GHC. Hugs implements TRex, one extensible record variant. The problem is that the record design space is large, and seems to lack local optima. And all reasonable variants break backward compatibility. As a result, nothing much happens.