Haskell Program to Check the birthday and print Happy Birthday message

In Haskell, this program will help us in checking the current date against a specified birthday and prints a "Happy Birthday" message if it is a match otherwise, it will print “Not your birthday yet”. Haskell provides function to fetch the current date and also to specify a date. This program can be implemented by using various approaches including the use of toGregorian function, fromGregorian function or by using utctDay <$> getCurrentTime.

This program will only check the birthday once, when the program runs. If we want the program to check the birthday periodically or at a specific time, we can use a library like timer or schedule, to schedule the check at a specific interval.

Method 1: Using toGregorian function

This method uses the Data.Time library to get the current date and the toGregorian function to extract the day and month of the current date.

Then it compares the current day and month to the specified birthday, and if they match, it prints "Happy Birthday!" otherwise it prints "Not your birthday yet."

Algorithm

• Step 1 − Data.Time module is imported.

• Step 2 − The specified birthday is defined as a day and month..

• Step 3 − Program execution will be started from main function. The main() function has whole control of the program. It is written as main = do..

• Step 4 − The current date is fetched by using getCurrentTime and toGregorian function..

• Step 5 − The current day and month is compared to the birthday specified above and final output is displayed.

Example

In the following example. We are going to check the birthday and print Happy Birthday message using toGregorian function.

import Data.Time
birthday :: (Int, Int)
birthday = (12, 25)
main :: IO ()
main = do
   today <- getCurrentTime
   let (_, month, day) = toGregorian $ utctDay today
   if (month, day) == birthday
   then putStrLn "Happy Birthday!"
   else putStrLn "Not your birthday yet."

Output

Not your birthday yet.

Method 2: Using fromGregorian function

In this method , the getZonedTime function is used to get the current date and time in the time zone, and the zonedTimeToLocalTime function is used to extract the local date and time, which is stored in now_time variable. The fromGregorian function is used to create a Day value from year, month and day integers, then LocalTime data constructor is used to create a LocalTime value by combining the Day value with a TimeOfDay value.

Algorithm

• Step 1 − Data.Time.LocalTime and Data.Time.Calendar modules are imported.

• Step 2 − The birthday is defined as a LocalTime by using fromGregorian function.

• Step 3 − Program execution will be started from main function. The main() function has whole control of the program.

• Step 4 − The current date is fetched and compared.

• Step 5 − The final output is displayed after the comparison.

Example

In this example, we are going to check the birthday and print Happy Birthday message using fromGregorian function

import Data.Time.LocalTime
import Data.Time.Calendar
birthday :: LocalTime
birthday = LocalTime (fromGregorian 2022 12 25) (TimeOfDay 12 0 0)
main :: IO ()
main = do
   now <- getZonedTime
   let now_time = zonedTimeToLocalTime now
   if now_time == birthday
   then putStrLn "Happy Birthday!"
   else putStrLn "Not your birthday yet."

Output

Not your birthday yet.

Method 3: using fromGregorian function and utctDay <$> getCurrentTime.

In this method , the Data.Time module and it's Day type which is a newtype wrapper around a Integer representing days since the epoch (January 1, year 1) is used. The fromGregorian function is used to create a Day value from year, month and day integers. And the utctDay <$> getCurrentTime is used to get the current date and time in UTC, and extracts the day from the current date. Then it compares the current day to the specified birthday, and if they match, it prints "Happy Birthday!" otherwise it prints "Not your birthday yet."

Algorithm

• Step 1 − Data.Time module is imported.

• Step 2 − The specified birthday is defined as a day using fromGregorian function.

• Step 3 − Program execution will be started from main function. The main() function has whole control of the program. It is written as main = do.

• Step 4 − The current date is fetched using utctDay <$> getCurrentTime.

• Step 5 − The final output is displayed on comparing the specified birthday and current date fetched.

Example

In this example, we are going to using fromGregorian function and utctDay <$> getCurrentTime

import Data.Time
birthday :: Day
birthday = fromGregorian 2022 12 25
main :: IO ()
main = do
   today <- utctDay <$> getCurrentTime
   if (today == birthday)
   then putStrLn "Happy Birthday!"
   else putStrLn "Not your birthday yet."

Output

Not your birthday yet.

Conclusion

In Haskell, the specified birthday is defined and current date is fetched. And this specified birthday is being compared by the current date fetched, and if it is same then output is printed as Happy Birthday message or else it will display Not your birthday yet. It can be achieved by various approaches including the use of toGregorian function, fromGregorian function or by using utctDay <$> getCurrentTime.