tail → drop 1

Suppose there are no primes in [m..n]:

• find (\(a, b) -> b-a == g) . uncurry zip . (id &&& drop 1) . filter isPrime $ [m..n] →
• find (\(a, b) -> b-a == g) . uncurry zip . (id &&& drop 1) $ [] →
• find (\(a, b) -> b-a == g) . uncurry zip $ ([], []) →
• find (\(a, b) -> b-a == g) [] →
• Nothing

Which is exactly what supposed to happen:

function should return the first pair of two prime numbers spaced with a gap of g between the limits m, n if these numbers exist otherwise Nothing.

What will happen if there is no prime in [m..n]?