= Solution
Include nonpositive counts and exhausted input explicitly:
``
take :: Int -> [a] -> [a]
take n _ | n <= 0 = []
take _ [] = []
take n (x:xs) = x : take (n-1) xs
drop :: Int -> [a] -> [a]
drop n xs | n <= 0 = xs
drop _ [] = []
drop n (_:xs) = drop (n-1) xs
``
The tests on the count precede inspection of the input <list>. Thus `take 0 undefined = []`, while `drop 0 undefined = undefined`, exactly as these <list prefix> and <list suffix> operations require. No element value is inspected merely to traverse the spine.<Haskell 2010 Language Report>[Chapter 9, PreludeList: take and drop]{ref}
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