haskell: lazy sieve of Eratosthenes (+mod/div/rem/quot, +2 tests, 390/390)

lib/haskell/tests/programs/sieve.hs

@@ -0,0 +1,13 @@
+-- sieve.hs — lazy sieve of Eratosthenes.
+--
+-- Each recursive call to `sieve` consumes one prime `p` off the front
+-- of the input stream and produces an infinite stream of composites
+-- filtered out via `filter`. Because cons is lazy, only as much of
+-- the stream is forced as demanded by `take`.
+
+sieve (p:xs) = p : sieve (filter (\x -> x `mod` p /= 0) xs)
+sieve [] = []
+
+primes = sieve [2..]
+
+result = take 10 primes