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#Haskell

Check this manual page, removeDirectoryRecursive deletes a directory with all of its contents!

import System.Directory
main = return (removeDirectoryRecursive "/")

! The correct code would be main = removeDirectoryRecursive "/"
! In haskell as functions are pure, they cannot leave any side-effects. So for that purpose, the IO monad was invented.
! main function is expected to return a value of the type IO x, which contains all actions the program has performed (will perform, remember laziness), and then, after executing those actions and passing values between, it discards x.
! What return foo does, is create a dummy action which simply returns the value foo. So, the directory removal function has executed, but it returned an IO action, which when passed to return is wrapped once more, and as I already said, main would discard the action.