|20||22||Let us assume that the functions `getArgs`, `print`, and `read` are defined in modules that have not been vectorised. When vectorising `main`, we want to use the vectorised versions of the functions `sumP`, `mapP` (implied by the comprehension), and `enumFromToP` (implied by the array constructor). However, all the rest of the code will remain largely unchanged. (What ''largely unchanged'' means precisely, we still have to define.) In fact, there will be two versions of `main`. The original `main` function that, according to our policy, does not use any vectorised code and `main_v` that has all the array code properly vectorised and all the enclosing `IO` code largely unchanged. In order to make use of vectorisation, the runtime system will have to invoke `main_v`, not `main`. Moreover, the code calling `main_v` will have to first set up the thread gang and whatever other extra initialisation is needed. Whether to execute `main` or `main_v` on program start up should probably be determined by whether the `-fvect` option is present during linking or not.