Remove existential types in TUI

[hasufell]

ghcup-hs/lib-tui/GHCup/Brick/Widgets/Menu.hs

Lines 111 to 153 in d94ce2a

	data FieldInput a b n =
	FieldInput
	{ inputState :: b -- ^ The state of the input field (what's rendered in the screen)
	, inputValidator :: b -> Either ErrorMessage a -- ^ A validator function
	, inputHelp :: HelpMessage -- ^ The input helpMessage
	, inputRender :: Bool
	-> ErrorStatus
	-> HelpMessage
	-> Label
	-> b
	-> (Widget n -> Widget n)
	-> (Widget n, Maybe (Widget n)) -- ^ How to draw the input and optionally an overlay, with focus a help message and input.
	-- A extension function can be applied too
	, inputHandler :: BrickEvent n () -> EventM n b () -- ^ The handler
	}
	makeLensesFor
	[ ("inputState", "inputStateL")
	, ("inputValidator", "inputValidatorL")
	, ("inputName", "inputNameL")
	, ("inputHelp", "inputHelpL")
	]
	''FieldInput
	-- | The MenuField is an existential type which stores a Lens' to a part of the Menu state.
	-- In also contains a Field input which internal state is hidden
	data MenuField s n where
	MenuField ::
	{ fieldAccesor :: Lens' s a -- ^ A Lens pointing to some part of the state
	, fieldInput :: FieldInput a b n -- ^ The input which modifies the state
	, fieldLabel :: Label -- ^ The label
	, fieldStatus :: ErrorStatus -- ^ Whether the current is valid or not.
	, fieldName :: n
	} -> MenuField s n
	isValidField :: MenuField s n -> Bool
	isValidField = (== Valid) . fieldStatus
	makeLensesFor
	[ ("fieldLabel", "fieldLabelL")
	, ("fieldStatus", "fieldStatusL")
	]
	''MenuField

These types must go. It's impossible to derive or write a lens for fieldInput.