unzipPairs :: [(a, b)] -> ([a], [b])
unzipPairs list = foldl (\(l1, l2) (c, d) -> (l1 ++ c, l2 ++ d)) ([], []) list


main.hs:2:75: error:
    • Occurs check: cannot construct the infinite type: a ~ [a]
      Expected type: [([a], [b])]
        Actual type: [(a, b)]
    • In the third argument of ‘foldl’, namely ‘list’
      In the expression:
        foldl (\ (l1, l2) (c, d) -> (l1 ++ c, l2 ++ d)) ([], []) list
      In an equation for ‘unzipPairs’:
          unzipPairs list
            = foldl (\ (l1, l2) (c, d) -> (l1 ++ c, l2 ++ d)) ([], []) list
    • Relevant bindings include
        list :: [(a, b)] (bound at main.hs:2:12)
        unzipPairs :: [(a, b)] -> ([a], [b]) (bound at main.hs:2:1)
  |
2 | unzipPairs list = foldl (\(l1, l2) (c, d) -> (l1 ++ c, l2 ++ d)) ([], []) list
  |