I am looking for a function

f::Eq a => [a]->[a]

that takes a list and returns the longest

initial segment of the list for which all

the elements are distinct.

For example f [2,3,6,4,3,5] = [2,3,6,4].

I didn't see anything that matched using Hoogle,

but I thought this might be a common enough

operation that this function might exists somewhere

in the standard packages.