The best way to kick the tyres on this kind of question is to plug in something literally infinite. That way if you arrive at an answer you're probably doing s

The best way to kick the tyres on this kind of question is to plug in something literally infinite. That way if you arrive at an answer you're probably doing something right with regard to space and time usage. For example, use all the prime numbers as an expression in your chain. import Data.Function import Data.Numbers.Primes main = do let result :: [Int] = primes & filter (startingWithDigit '5') & asPairs & map pairSum & drop 100000 & take 10 print result asPairs xs = zip xs (tail xs) pairSum (a, b) = a + b startingWithDigit d x = d == head (show x) > [100960734,100960764,100960792,100960800,100960812] > 3 MiB total memory in use (0 MB lost due to fragmentation)