nice kata! such a cool idea
too bad it's Haskell specific, I would like to share it with everybody! ;-(

it should say "one at a time" instead of "on at a time"

in the Haskell version, the type should be Integer -> Integer, not a -> a. in Haskell It's impossible to have a doubling function of the type a -> a.

the description should be more helpful

wtf am i supposed to do? this is so unanderstandale

this kata didn't tell in the description that large inputs will be tested on, thus requiring the solution to be more efficient than the idiomatic version.

please change "the number of intersections on the map" to "the amount of intersectons" or "the max of an intersection's value", these are much clearer ways to say it.
also, as some people pointed out already, if you test on large maps you should tell it in the description.

this could be much easier in haskell due to lazy code.