An alternative frontend for Haskell?

[AntC2]

@gilmi

In a language with first class records like PureScript, field selector like the ones in Haskell are irrelevant because they don’t work on the data type Tree, they work on the payload of Node. So your snippet becomes:

incTree = case _ of
  Nil -> Nil
  Node r ->
    Node (r { value = r.value + 1 })

You can get that code accepted in Haskell today (or even in H98 except for the r.value: use value r instead). You need

data Tree a
      = Nil
      | Node (Node' a)
data Node' a = MkNode{ value :: a, left :: Tree a, right :: Tree a }

IOW, just as with purescript, nest an extra constructor to express the field names. You might even be able to use the auxiliary Node' within other data types; in effect re-using the field names.

So your ‘Alternative front end’ could support some syntactic sugar to make those decls less verbose.

There are good reasons to introduce free-standing first-class records/global field labels into a Haskell, but merely to avoid partial access is not one of them: I suspect the nested-constructor here will be just annoying enough people will define direct extractor functions – and you’re back to partiality.