Step by Step solution about How to resolve the algorithm Calendar step by step in the Haskell programming language

The code provided is a Haskell program that prints a calendar for a given year. It uses the Data.Time, Data.Time.Calendar, Data.Time.Calendar.WeekDate, Data.List.Split, and Data.List libraries.

The code first defines the data types Day and Month to represent days and months, respectively. It then defines a function monthToInt to convert a month to an integer.

The dayFromDate function takes a year, a month, and a day and returns the day of the week for that date. It uses the toWeekDate function from the Data.Time.Calendar.WeekDate library to convert the date to a week date and then uses the mod operator to find the day of the week.

The nSpaces function takes an integer n and returns a Text string containing n spaces. The space variable is a Text string containing a single space.

The calMarginWidth variable is an integer that specifies the width of the margin around the calendar. The calMargin variable is a Text string containing the margin.

The calWidth variable is an integer that specifies the width of the calendar.

The listMonth function takes a year and a month and returns a list of Text strings representing the calendar for that month. The first element of the list is the header for the month, the second element is the header for the week, and the remaining elements are the weeks of the month.

The monthHeader variable is a Text string containing the header for the month. It is centered within the calendar using the center function from the Text library.

The weekHeader variable is a Text string containing the header for the week. It is created by concatenating the Text strings for each day of the week using the intercalate function from the Text library.

The monthLength variable is an integer that specifies the length of the month. It is calculated using the gregorianMonthLength function from the Data.Time.Calendar library.

The firstDay variable is an integer that specifies the day of the week on which the month begins. It is calculated using the dayFromDate function.

The days variable is a list of Text strings representing the days of the month. It is created by replicating the nSpaces string firstDay times and then appending the Text strings for each day of the month using the map function from the Data.List library.

The weeks variable is a list of Text strings representing the weeks of the month. It is created by splitting the days list into chunks of 7 elements using the chunksOf function from the Data.List.Split library and then justifying each chunk to the left within the calendar using the justifyLeft function from the Text library.

The weeks' variable is a list of Text strings representing the weeks of the month with any remaining empty weeks filled with spaces. It is created by appending the nSpaces string to the weeks list until it has a length of 6.

The listCalendar function takes a year and the number of columns to use and returns a list of lists of lists of Text strings representing the calendar for that year. The first level of the list represents the months of the year, the second level represents the weeks of the month, and the third level represents the days of the week.

The calColFromCol function takes the number of columns in the calendar and the column number and returns the calendar column for that column. It uses the divMod function from the Prelude library to calculate the column and row of the calendar corresponding to the column number.

The colFromCalCol function takes the calendar column number and returns the column number in the calendar. It uses the * and + operators to calculate the column number.

The center function takes a string and a width and returns a Text string that is centered within the specified width. It uses the center function from the Text library.

The printCal function takes a list of lists of lists of Text strings and prints the calendar to the console. It uses the mapM_ function from the Control.Monad library to print each row of the calendar.

The printCalendar function takes a year and the number of columns to use and prints the calendar to the console. It first checks if the number of columns is less than 20. If it is, it prints an error message to the console. Otherwise, it prints the year and the calendar to the console.

import qualified Data.Text as T
import Data.Time
import Data.Time.Calendar
import Data.Time.Calendar.WeekDate
import Data.List.Split (chunksOf)
import Data.List

data Day = Su | Mo | Tu | We | Th | Fr | Sa
           deriving (Show, Eq, Ord, Enum)

data Month = January | February | March
           | April   | May      | June
           | July    | August   | September
           | October | November | December
             deriving (Show, Eq, Ord, Enum)

monthToInt :: Month -> Int
monthToInt = (+ 1) . fromEnum

dayFromDate :: Integer -> Month -> Int -> Int
dayFromDate year month day = day' `mod` 7
    where (_, _, day') = toWeekDate $ fromGregorian year (monthToInt month) day

nSpaces :: Int -> T.Text
nSpaces n = T.replicate n (T.pack " ")

space :: T.Text
space = nSpaces 1

calMarginWidth = 3

calMargin :: T.Text
calMargin = nSpaces calMarginWidth

calWidth = 20

listMonth :: Integer -> Month -> [T.Text]
listMonth year month = [monthHeader, weekHeader] ++ weeks'
    where
      monthHeader = (T.center calWidth ' ') . T.pack $ show month

      weekHeader = (T.intercalate space) $ map (T.pack . show) [(Su)..]

      monthLength = toInteger $ 
                    gregorianMonthLength year $
                    monthToInt month

      firstDay = dayFromDate year month 1

      days = replicate firstDay (nSpaces 2) ++
             map ((T.justifyRight 2 ' ') . T.pack . show) [1..monthLength]

      weeks = map (T.justifyLeft calWidth ' ') $
              map (T.intercalate space) $
              chunksOf 7 days

      weeks' = weeks ++ replicate (6 - length weeks) (nSpaces calWidth)

listCalendar :: Integer -> Int -> [[[T.Text]]]
listCalendar year calColumns = (chunksOf calColumns) . (map (listMonth year)) $
                               enumFrom January

calColFromCol :: Int -> Int
calColFromCol columns = c + if r >= calWidth then 1 else 0
    where (c, r) = columns `divMod` (calWidth + calMarginWidth)

colFromCalCol :: Int -> Int
colFromCalCol calCol = calCol * calWidth + ((calCol - 1) * calMarginWidth)

center :: Int -> String -> String
center i a = T.unpack . (T.center i ' ') $ T.pack a

printCal :: [[[T.Text]]] -> IO ()
printCal = mapM_ f where
  f c = mapM_ (putStrLn . T.unpack) rows
    where rows = map (T.intercalate calMargin) $ transpose c

printCalendar :: Integer -> Int -> IO ()
printCalendar year columns =
    if columns < 20
    then putStrLn $ "Cannot print less than 20 columns"
    else do
      putStrLn $ center columns' "[Maybe Snoopy]"
      putStrLn $ center columns' $ show year
      putStrLn ""
      printCal $ listCalendar year calcol'
    where
      calcol' = calColFromCol columns

      columns' = colFromCalCol calcol'