How to write a generic function that updates fields of a Record

Question

Consider

type alias Rec = { a: Int, b: Int, c:Int }
updateRec r aVal            = { r|a = aVal } 
updateRec2 r aVal bVal      = { r|a = aVal, b= bVal } 
updateRec3 r aVal bVal cVal = ...

How to generalize updateRec and updateRec2... into one function?

Answer 1

Here's a better way of doing the same thing:

updateA : Int -> Rec -> Rec
updateA x rec = { rec | a = x }

-- Similarly for b, c

Now you can do the following, supposing you already have a value rec : Rec you want to update:

myUpdatedRec : Rec
myUpdatedRec =
  rec 
  |> updateA 7
  |> updateB 19

You can now update an arbitrary number of fields by stringing together |> updateX ....