The word "operator" need not imply "a built-in construct"; instead it's often used to describe a name made up of symbols, which is how it appears to be used here. In F#, for instance, where |> is used frequently because it improves type inference, it is defined in the standard library as `let (|>) x f = f x` (note that the definition you give is actually for the related (>>) operator). Would you claim that someone is "doing it wrong" because they call (+) the "addition operator"?