# Permutations of a list: - haskell: perms [] = [[]] perms xs = [ x:ps | x <- xs , ps <- perms ( xs\\[x] ) ] - js: (using https://github.com/tc39/proposa

# Permutations of a list: - haskell: perms [] = [[]] perms xs = [ x:ps | x <- xs , ps <- perms ( xs\\[x] ) ] - js: (using https://github.com/tc39/proposal-slice-notation https://github.com/tc39/proposal-slice-notation for conciseness) const perms = xs => xs.length === 0 ? [[]] : xs.flatMap((xi, i) => perms([...xs[0:i], ...xs[i+1:]).map(xsi => [xi, ...xsi]) # Cartesian product of 2 or n lists - haskell: cart2 xs ys = [(x,y) | x <- xs, y <- ys] cartn :: [[a]] -> [[a]]; cartn [] = [[]] cartn(xs:xss) = [x:ys | x <- xs, ys <- yss] where yss = cartn xss - js: const cart2 = (xs, ys) => xs.flatMap(x => ys.map(y => [x,y])); const cartn = (...args) => args.reduce((yss, xs) => yss.flatMap(ys => xs.map(x => [...ys, x])), [[]]); // or recursive const cartn = (xs, ...xss) => xss.length === 0 ? xs : xs.flatMap(x => cartn(...xss).map(y => [x,y]))