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