Haskell Program to add two numbers

Program

main = do
 let a = 10
 let b = 20
 putStrLn "Sum of two numbers is:"
 print (a + b)

Output

$ ghc add_two_numbers.hs 
[1 of 1] Compiling Main             ( add_two_numbers.hs, add_two_numbers.o )
Linking add_two_numbers ...
$ ./add_two_numbers 
Sum of two numbers is:
30