#unfoldr
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musuwi.mom
behold: my best attempt at printing the first 10,000 primes in rust, lua, fennel and haskell
fn gen_primes_faster(count: usize) -> Vec<u32> { let mut primes = Vec::with_capacity(count); for _ in 0..count { let last = primes.last().unwrap_or(&1); let next = (*last + 1..) .find(|n| { !primes .iter() .take_while(|p| *p * *p <= *n) .any(|p| n % p == 0) }) .unwrap(); primes.push(next); } primes } fn main() { println!("generating primes:"); let primes = gen_primes_faster(10000) .into_iter() .map(|u| u.to_string()) .collect::<Vec<_>>() .join(", "); println!("{primes}"); } local function next_prime(primes) local n = primes[#primes] local n_is_prime repeat n = n + 1 n_is_prime = true for _, p in ipairs(primes) do if p * p > n+1 then break end if n % p == 0 then n_is_prime = false break end end until n_is_prime return n end local function gen_primes(count) local primes = {2} for _ = 2, count do local next = next_prime(primes) table.insert(primes, next) end return primes end local primes = table.concat(gen_primes(10000), ", ") print(primes) (fn prime? [n i primes] (let [p (. primes i)] (if (= (% n p) 0) false (> (* p p) n) true (prime? n (+ i 1) primes)))) (fn next-prime [primes ?n] (let [n (or ?n (+ 1 (. primes (length primes))))] (if (prime? n 1 primes) n (next-prime primes (+ n 1))))) (fn gen-primes [count] (var primes [2]) (for [_ 2 count] (table.insert primes (next-prime primes))) primes) (local primes (table.concat (gen-primes 10000) ", ")) (print primes) import Data.List import Data.Maybe isPrime n p's = all (\p -> n `mod` p /= 0) (takeWhile (\p -> p^2 <= n) (reverse ps)) nextPrime :: [Int] -> Int nextPrime [] = 2 nextPrime p's = fromJust (find (\n -> isPrime n p's) [(head p's + 1)..]) primes = unfoldr (\list -> let next = nextPrime list in Just (next, next : list)) [] primeString x = intercalate ", " (map show (take x primes)) main = putStrLn (primeString 10000)
January 7, 2025 at 12:52 AM
lirelum.bsky.social
oomfAddition a b = unfoldr (\x -> Just (x + 1, x + 1)) a !! b

:)
May 7, 2025 at 3:08 PM
bekavalentine.bsky.social
the authors mention that the earlier, and more widespread, fusion techniques of build/foldr fusion and destroy/unfoldr fusion, as well as and older variant of stream fusion, did not suffice to produce this rather gnarly fusion
August 25, 2025 at 7:37 AM
philip-schwarz.bsky.social
🚀 just uploaded (link in reply): "List Unfolding -
unfold as the Computational Dual of fold,
and how unfold relates to iterate" #folding #unfolding #fold #unfold #foldL #foldL_prime #unfoldL #unfoldL_prime #unfoldr #iterate #anamorphism #catamorphism #functional_programming #scala #haskell
May 31, 2025 at 10:46 AM