Henry Laxen
It seems to me this should be easy, but I can't quite figure out how to do it without a lot of typing. Here is the question:
Suppose you have a data type like: Data Foo = Foo { a :: Int, b :: Int, ... many other fields ... y :: Int } deriving (Eq, Read, Show, Typeable, Data)
Now I would like to add a field z :: Int to the end of Foo. If I have a ton of data out on disk, which I wrote with, say writeFile "a.data" (show foo) -- where foo is a [Foo] say 1000 long, I would like to get a new "a.data" file which has a new z::Int field.
One approach to this would be to temporarily redefine Foo data Foo = Foo { a :: Int, b :: Int, ... many other fields ... y :: Int } deriving (Eq, Read, Show, Typeable, Data) | NuFu {a :: Int, b :: Int, ... many other fields ... y :: Int, z :: Int} deriving (Eq, Read, Show, Typeable, Data) read the file, map Foo to NuFoo + whatever the initial value of z is and write it out again. -- Jón Fairbairn Jon.Fairbairn@cl.cam.ac.uk