:seti -XDataKinds -XTemplateHaskell
import Language.Haskell.TH
import Data.Proxy

data (:::) = forall k k' . k ::: k'; infixr 5 :::

intT = ConT ''Int
stringT = ConT ''String
boolT = ConT ''Bool

:t Proxy @($(pure $ UInfixT intT '(:::) stringT))

promUInf x y = PromotedUInfixT x (mkName ":::") y
:t Proxy @($(pure $ (intT `promUInf` stringT) `promUInf` boolT))

promInf x y = PromotedInfixT x (mkName ":::") y
:t Proxy @($(pure $ (intT `promInf` stringT) `promInf` boolT))