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> The new multi-sequence syntax allows you to loop over two or more arrays or slices at the same time In Haskell, this is called a parallel list comprehension:

• masklinn 4y ago
  No, your list comprehension is a product (it iterates ys for every x). The feature here is zip.
  • tuukkah 4y ago
    I'll quote from the documentation link I referenced: > For example, the following zips together two lists: [ (x, y) | x <- xs | y <- ys ] That's precisely the difference between a normal list comprehension (one pipe) and a parallel list comprehension (multiple pipes). For clarity, here's your normal list comprehension (with one pipe) that produces all the combinations instead: [ (x, y) | x <- xs, y <- ys ] And here's the full example from the article converted to Haskell and producing the exact same output: {-# LANGUAGE ParallelListComp #-} import Control.Monad (mapM) elems = [ "water", "earth", "fire", "air" ] nats = [ "tribes", "kingdom", "nation", "nomads" ] main = mapM putStrLn [ show idx ++ " - " ++ e ++ " " ++ n | e <- elems | n <- nats | idx <- [0..] ] EDIT: I suppose an explicit zip with an anonymous function looks more idiomatic though: main = forM (zip3 elems nats [0..]) $ \(e, n, idx) -> putStrLn (show idx ++ " - " ++ e ++ " " ++ n) EDIT2: Best of both worlds with the list monad? main = mapM putStrLn $ do (e, n, idx) <- zip3 elems nats [0..] [ show idx ++ " - " ++ e ++ " " ++ n ]