如何在 Haskell 中将数字列表转换为字符串列表

Question

How to convert list of numbers to list of strings(one string = one number from list) in Haskell.

[Int] -> [String]

Examples: [1,2,3,4] -> ["1","2","3","4"]

Answer 1

If you have a function f :: a -> b , then map f :: [a] -> [b] applies f on all the list elements.

The function show can convert "printable" types in their string representation. In particular, one of the possible types for show is Int -> String .

Use both tools.

Answer 2

If you need to write a function to print an element from 0, this could be another solution

cp_log :: (Show a) => [a] -> String

cp_log [] = ""
cp_log [x] = (show x)
cp_log (x:xs) = (show x) ++ ", " ++ cp_log xs

A complete example can be the following one

cp_log :: (Show a) => [a] -> String
    
cp_log [] = ""
cp_log [x] = (show x)
cp_log (x:xs) = (show x) ++ ", " ++ cp_log xs

quick_sort :: (Ord a) => [a] -> [a]
quick_sort [] = []
quick_sort (x:xs) =
  let smaller = quick_sort [a | a <- xs, a <= x]
      bigger = quick_sort [a | a <- xs, a > x]
  in smaller ++ [x] ++ bigger

main =
  let sorted = (quick_sort [4, 5, 3, 2, 4, 3, 2])
  in putStrLn (cp_log sorted)

Answer 3

Using the list monad:

f :: [Int] -> String
f xs = do 
         x <- xs
         return $ show x 

or equivalently:

f' :: [Int] -> [String]
f' = (>>= return.show)