simple Haskell loop

Question

I just started learning Haskell, but the absence of loops is infinitely frustrating right now. I figured out how to write loops for functions. My problem, however, is that I want to output some results while iterating the loop. It seems that I have to use debug to perform this simple task.

So right now I would just appreciate an example of how to print out a string 10 times in the main structure.

In other words, I want to do this 10 times:

main = do       putStrLn "a string"  

Thanks. I feel this will be very illuminating for my task.

Answer 1

You could define a recursive function that prints "a string" n times (n being the parameter of the function), like this:

printStringNTimes 0 = return () printStringNTimes n =  do   putStrLn "a string"   printStringNTimes (n-1)  main = printStringNTimes 10 

A somewhat more general approach would be to define a function that repeats any IO action n times:

repeatNTimes 0 _ = return () repeatNTimes n action =  do   action   repeatNTimes (n-1) action  main = repeatNTimes 10 (putStrLn "a string") 

The above function already exists in Control.Monad under the name replicateM_.