I suggest to include this operator in "Data.Maybe" and "Prelude".

    (?:) :: Maybe a -> a -> a

    maybeA ?: b = fromMaybe b maybeA

    1.

        maybeValue ?: error "Value is unexpectedly empty. This is a bug."

    instead of

        fromMaybe (error "Value is unexpectedly empty. This is a bug.") maybeValue

    2.

        maybeA ?: maybeB ?: c

    instead of

        fromMaybe (fromMaybe c maybeB) maybeA

    

    Hayoo search gives only 6 collisions with 5 hardly fundamental libraries.

* The nickname and the operator itself are inspired by the ones from Groovy language.

** The symbols of the operator are a reminder of plain old ternary construct.

*** To understand the nickname look at the operator as on emoticon.