[Haskell-cafe] Text.Regex.matchRegex: Success is empty?

Esteemed Haskellers, It is working for me, but I am puzzled by the matchRegex function: > import Text.Regex > :i matchRegex matchRegex :: Regex -> String -> Maybe [String] -- Defined in ‘Text.Regex’ Searches that fail return Nothing: > matchRegex (mkRegex "z") "abracadabra" Nothing which makes sense. But why do searches that succeed return an empty list of Strings? > matchRegex (mkRegex "a") "abracadabra" Just [] > -- Jeffrey Benjamin Brown