import Data.List

lengthUpToRepeat (p++[r]++q) 
    | nub p == p && r `elem` p 
    = length p + 1

main = lengthUpToRepeat [1,2,3,42,56,0,1]

-- however, this does not terminate
-- main = lengthUpToRepeat ([1,2,3,42,56]++[0..])