@hackage template-default0.1

Declaring instances of the Default type class has always been pretty mechanical. This package makes the compiler do the mechanical bit. This has the benefit that even less thought is required, and the instance will automatically be corrected when the definition of the data type changes (say, to add more arguments to the constructor). Usage looks like this:

(-# LANGUAGE TemplateHaskell #-)
import Data.Default.TH
deriveDefault ''MyFancyTypeName