Step by Step solution about How to resolve the algorithm Keyboard input/Obtain a Y or N response step by step in the Haskell programming language

The provided Haskell code is designed to read a single character from the user's input and interpret it as a confirmation or denial. It does this by repeatedly reading characters until it encounters either 'Y', 'N', 'y', or 'n', and then interpreting the input accordingly.

A step-by-step explanation of the code:

1. The hFlushInput function is defined to consume all pending input from a specified file handle. This ensures that any characters entered by the user before the program prompts for input are discarded.

2. The yorn function is defined to read a single character from the user's input and interpret it as either 'Y' (yes) or 'N' (no). It handles both uppercase and lowercase input. If the input character is not recognized, it recursively calls yorn until a valid character is entered.

3. The main function is the entry point of the program. It first sets the buffering mode of the standard output (stdout) and standard input (stdin) to NoBuffering, which means that characters will be written to the console immediately and input will be read character by character.

4. It then displays the prompt "Press Y or N to continue: " to the user.

5. The hSetEcho stdin False call disables character echoing for stdin, which means that the characters entered by the user will not be displayed on the console.

6. The hFlushInput stdin call is made to consume any pending input from stdin, ensuring that the user's response is not affected by any previous input.

7. The yorn function is called to read the user's input and interpret it as a confirmation or denial. The result is stored in the answer variable.

8. Finally, the program prints the character entered by the user to the console.

In summary, this code is a simple command-line program that prompts the user for a single character ('Y' or 'N') and interprets it as a confirmation or denial. It ensures that the user's input is not influenced by previous input and that the characters entered are not echoed to the console.

import System.IO

hFlushInput :: Handle -> IO ()
hFlushInput hdl = do
  r <- hReady hdl
  if r then do
    c <- hGetChar hdl
    hFlushInput hdl
  else
    return ()

yorn :: IO Char
yorn = do
  c <- getChar
  if c == 'Y' || c == 'N' then return c
  else if c == 'y' then return 'Y'
  else if c == 'n' then return 'N'
  else yorn

main :: IO ()
main = do
  hSetBuffering stdout NoBuffering
  putStr "Press Y or N to continue: "

  hSetBuffering stdin NoBuffering
  hSetEcho stdin False
  hFlushInput stdin
  answer <- yorn
  putStrLn [answer]