I’m trying to write HTML form helpers where I’d like the call-sites to support both of the following use-cases:

data FormCtx obj = { ctxFieldNamePrefix :: !Text, ctxObject :: !obj } 
data MyRecord = MyRecord { field1 :: !Text, field2 :: !Text } deriving (Generic)

-- USE-CASE #1
let ctx = FormCtx "MyRecord" obj
fieldNameFor @"field1" ctx

-- USE-CASE #2 -- with a (Maybe obj)
let ctx = FormCtx "MyRecord" (Just obj)
fieldNameFor @"field1" ctx

-- Implementation for fieldNameFor which works only 
-- with `obj`, and not `Maybe obj`
fieldNameFor :: forall.k obj a . (KnownSymbol k, HasField k obj a) => FormCtx obj -> Text
fieldNameFor FormCtx {ctxFieldNamePrefix} = ctxFieldNamePrefix <> "[" <> (Text.pack $ symbolVal (Proxy @k)) <> "]"

I’ve tried defining a type-classs, called FieldNameFor to be able to define overlapping instances for obj and Maybe obj but I’m unable to make it work with the KnownSymbol k, HasField k obj a typeclass constrains that are required for getField to work.