How to Print the Same Characters In A Row In Haskell?

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To print the same characters in a row in Haskell, you can use the replicate function to create a list of the desired characters and then concatenate them using the concat function.


Here's a simple example that prints the character 'a' ten times in a row:

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main :: IO ()
main = do
    let characters = replicate 10 'a'
    putStrLn $ concat characters


In this example, replicate 10 'a' creates a list ['a', 'a', 'a', 'a', 'a', 'a', 'a', 'a', 'a', 'a'], and concat is used to concatenate these characters into a single string. Finally, putStrLn is used to print the string to the console. You can replace 'a' and 10 with any characters and number, respectively, to print different characters and different number of times.

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How to print characters in reverse order in Haskell?

There are multiple ways to print characters in reverse order in Haskell. Here are a few examples:

  1. Using Data.List module:
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import Data.List (reverse)

printReversed :: String -> IO ()
printReversed str = putStrLn (reverse str)

main :: IO ()
main = do
    let str = "Hello, World!"
    printReversed str


  1. Using recursion:
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printReversed :: String -> IO ()
printReversed [] = putStrLn ""
printReversed (x:xs) = do
    printReversed xs
    putChar x

main :: IO ()
main = do
    let str = "Hello, World!"
    printReversed str


  1. Using list comprehension:
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printReversed :: String -> IO ()
printReversed str = putStrLn [str !! i | i <- [length str - 1, length str - 2..0]]

main :: IO ()
main = do
    let str = "Hello, World!"
    printReversed str


All three approaches will print the characters of the input string in reverse order. In the first two approaches, the printReversed function takes a string as input and recursively prints the characters in reverse order. The last approach uses a list comprehension to create a new string with characters in reverse order and then prints it.


How to sort characters in a string alphabetically in Haskell?

One way to sort characters in a string alphabetically in Haskell is to convert the string into a list of characters, sort the list, and then convert it back into a string. Here is an example of how this can be done:

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import Data.List (sort)

sortString :: String -> String
sortString = sort . filter (/= ' ')

main :: IO ()
main = do
  input <- getLine
  let sortedString = sortString input
  putStrLn sortedString


In this example, the sortString function takes a string as input and performs the following steps:

  1. It first removes any spaces from the input string using the filter function.
  2. It then converts the string into a list of characters using Haskell's built-in String type which is just an alias for [Char].
  3. It applies the sort function from the Data.List module to sort the list of characters alphabetically.
  4. Finally, it converts the sorted list back into a string.


The main function reads a line of input from the user, applies sortString to it, and then prints the sorted string using putStrLn.


How to trim leading and trailing whitespace from a string in Haskell?

In Haskell, you can trim leading and trailing whitespace from a string using functions from the Data.Text module. Here's an example of how you can do it:

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import Data.Text (Text, pack, unpack, strip)

trim :: String -> String
trim = unpack . strip . pack


In this example, we first convert the input string into a Text value using the pack function. Then, we use the strip function to remove the leading and trailing whitespace from the Text value. Finally, we convert the trimmed Text value back to a string using the unpack function.


You can then use the trim function to trim leading and trailing whitespace from any string:

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main :: IO ()
main = do
  let str = "  Hello, World!   "
  let trimmedStr = trim str
  putStrLn trimmedStr


Output:

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Hello, World!


Note that the Data.Text module provides a more efficient and performant implementation for working with textual data than using the standard String type.


How to check if a character is a digit in Haskell?

In Haskell, you can use the isDigit function from the Data.Char module to check if a character is a digit. Here's an example usage:

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import Data.Char

isDigitChar :: Char -> Bool
isDigitChar c = isDigit c


In this example, the isDigitChar function takes a single character c as input and checks whether it is a digit using the isDigit function. The result of isDigit c is returned, indicating whether c is a digit or not.


You can test this function in GHCi or in your Haskell program as follows:

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main :: IO ()
main = do
    putStrLn $ show (isDigitChar '2') -- prints "True"
    putStrLn $ show (isDigitChar 'a') -- prints "False"


The show function is used to convert the Bool result to a String before printing it to the console.

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