simple Haskell loop

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_.

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