Haskell-Do while loop

while-loop do-while

Question

¡Soy nuevo para Haskell y estaría contento si alguien estuviera dispuesto a ayudarme! Estoy intentando que este programa funcione con un ciclo do while.

El resultado del segundo comando getLine se pone en el goGlenn variable y si goGlenn no es igual a "start", el programa volverá al principio

    start = do
    loop $ do lift performAction
        putStrLn "Hello, what is your name?"
        name <- getLine
        putStrLn ("Welcome to our personality test " ++ name ++ ", inspired by the Big Five Theory.") 
        putStrLn "You will receive fifty questions in total to which you can reply with Yes or No."
        putStrLn "Whenever you feel ready to begin please write Start"
        goGlenn <- getLine
        putStrLn goGlenn
    while (goGlenn /= "start")

Answer 1

En Haskell escribes "bucles" recursivamente, la mayoría de las veces.

import Control.Monad

-- ....

start = do
    putStrLn "Before the loop!"
    -- we define "loop" as a recursive IO action
    let loop = do
            putStrLn "Hello, what is your name?"
            name <- getLine
            putStrLn $ "Welcome to our personality test " ++ name 
                     ++ ", inspired by the Big Five Theory."
            putStrLn "You will receive fifty questions in total to which you can reply with Yes or No."
            putStrLn "Whenever you feel ready to begin please write Start"
            goGlenn <- getLine
            putStrLn goGlenn
            -- if we did not finish, start another loop
            when (goGlenn /= "start") loop
    loop  -- start the first iteration 
    putStrLn "After the loop!"

Answer 2

No estoy seguro, tal vez esta versión te puede ayudar a:

import Control.Monad

loop action = do
    condition <- action
    when condition (loop action)

while = return

start =
    let action = do {
        putStrLn "Hello, what is your name?";
        name <- getLine;
        putStrLn ("Welcome to our personality test " ++ name ++ ", inspired by the Big Five Theory.");
        putStrLn "You will receive fifty questions in total to which you can reply with Yes or No.";
        putStrLn "Whenever you feel ready to begin please write Start";
        goGlenn <- getLine;
        putStrLn goGlenn;
        while (goGlenn /= "start");
    }
    in loop action

(Editar) o puede ser también:

start =
    loop (do {
        putStrLn "Hello, what is your name?";
        name <- getLine;
        putStrLn ("Welcome to our personality test " ++ name ++ ", inspired by the Big Five Theory.");
        putStrLn "You will receive fifty questions in total to which you can reply with Yes or No.";
        putStrLn "Whenever you feel ready to begin please write Start";
        goGlenn <- getLine;
        putStrLn goGlenn;
        while (goGlenn /= "start");
    })