OptionalProperties.purs

type FooBar = { foo :: String , bar? :: Int }

r :: FooBar
r = { foo: "foo" }

foo :: String
foo = r.foo -- "foo"

bar :: Maybe Int
bar = r.bar -- Nothing

r1 :: FooBar
r1 = { foo: "foo", bar: 0 }  -- Same as current behavior

bar1 :: Maybe Int
bar1 = r.bar -- Just 0

r2 :: FooBar
r2 = { foo: "foo", bar:? Just 0 } -- :? absorbs the Maybe

bar2 :: Maybe Int
bar2 = r.bar -- Just 0

bool2 = r1 == r2 -- true

r3 :: FooBar
r3 = { foo: "foo", bar:? Nothing } -- :? absorbs the Maybe

bar3 :: Maybe Int
bar3 = r.bar -- Nothing

bool3 = r == r3 -- true

r4 :: FooBar
r4 = r { bar = 0 } -- Same as current behavior

bar4 :: Maybe Int
bar4 = r4.bar -- Just 0

r5 :: FooBar
r5 = r { bar =? Just 0 } -- =? absorbs the Maybe 

bar5 :: Maybe Int
bar5 = r5.bar -- Just 3

r6 :: FooBar
r6 = r { bar =? Nothing } -- =? absorbs the Maybe 

bar6 :: Maybe Int
bar6 = r6.bar -- Nothing

r7 = { foo: "foo", bar: Just 0 } -- { foo :: String, bar: Maybe Int }

bar7 :: Maybe Int
bar7 = r7.bar -- Just 0

r8 = { foo: "foo", bar:? Just 0 } -- { foo :: String, bar?: Int }

bar8 :: Maybe Int
bar8 = r8.bar -- Just 0

let
  { foo, bar } = r8
in
  { foo, bar? } :: FooBar
  
let
  { foo, bar } = r8
in
  { foo, bar } :: { foo :: String, bar :: Maybe Int }