Take a look at Data.Accessor on hackage:
http://hackage.haskell.org/cgi-bin/hackage-scripts/package/data-accessor
http://hackage.haskell.org/cgi-bin/hackage-scripts/package/data-accessor-tem...
-- ryan
On Sun, Mar 29, 2009 at 2:13 AM, Andrew Coppin
Haskell's record syntax is quite nice, for a number of reasons. However, suppose I have some record:
data Foobar = Foobar {foo1, foo2, foo3...}
Now suppose that foo3 :: [Int], and I want to prepend 5 to it. I end up having to write something like
let v1 = v0 {foo3 = 5 : (foo3 v0)}
If the field name isn't "foo" but something more descriptive, and the transformation to be applied to it is more intricate, you end up with quite a bit of code.
In summary, record syntax gives you a nice way of replacing the value of one field with something else, but no easy way to *modify* the existing value somehow.
Does anybody know of a way around this? Is there some trick I'm not seeing? Is there an extension or proposal that fixes this?
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