Shorthand way for assigning a single field in a record, while copying the rest of the fields?

Question

Let\'s say I have the following record ADT:

data Foo = Bar { a :: Integer, b :: String, c :: String }

I want a function that takes a record

Answer 1

You don’t need to define auxiliary functions or employ lenses. Standard Haskell has already what you need. Let’s take the example by Don Stewart:

data Foo = Foo { a :: Int, b :: Int , c :: String }

test = Foo 1 2 "Hello"

Then you can just say test { c = "Goodbye" } to get an updated record.