I said ( https://mail.haskell.org/pipermail/haskell-cafe/2024-December/136986.html) On Wed, 25 Dec 2024 at 16:49, Anthony Clayden wrote:

...

[**] I'm particularly keen on field names starting upper case, because they're injective/part of the structure, like data constructors.

And previously with Hugs ( https://mail.haskell.org/pipermail/hugs-users/2020-May/000927.html)

* I've taught Trex to support field labels starting upper-case, because,

well for me they're more like constructors than variables.

So can I combine that work? Yes, providing I use Upper-case labels only within `{ ... }`. These can combine lower with Upper field names within the same data type; can pun on the lower.

data Upup a = MkUp{ down :: a, Up :: Int } deriving (Eq, Show)

anUp = MkUp{ down = 'a', Up = 5 } -- build recUp = anUp{ Up = 7 } -- field update by Up label,

record syntax

succUp (MkUp {down, Up = u} ) = MkUp{ down = succ down, Up = succ u }

You can't use a field selection function: 'ERROR - "Up" is not a data constructor'. (It looks like Hugs does generate such a function; this error is a syntax rejection in trying to use it.)