[Haskell-cafe] Re: Adding a field to a data record

28 Jul 2009


      Malcolm Wallace  writes:
...
...
and perhaps use emacs to
query-replace all the Foo1's back to Foo's
At least this bit can be avoided easily enough, by using
module qualification during the conversion process.
module Original (Foo(..)) where
     data Foo = Foo { ... y :: Int } deriving ...
module New (Foo(..)) where
     data Foo = Foo { ... y, z :: Int } deriving ...
module Convert where
     import Original as Old
     import New as New
     newFoo :: Old.Foo -> New.Foo
     newFoo old{..} = New.Foo { a=a, b=b, ... z=1 }
Finally rename module New.
Regards,
     Malcolm
Thanks Malcolm, yes, that keeps me out of emacs, but the part I would really
like to avoid is writing the New.Foo { a=a, b=b, ... z=1 } part, where the field
names are many, long, and varied.  Yes, I could cut and paste, but I'm hoping
for a "better way."  Thanks.
Best wishes,
Henry Laxen