Is it possible to  use such  function: (data: N) => T as the parameter of the map method?

I'm using Typescript. The current map only accepts  functions like : fn: (data: N) => N. But in practice, I need to feed the map with function like : (data: N) => T. T is not the same type as N. Could you tell me how to do it?
Thank you so much!
```ts
public map<N>(fn: (data: N) => N): Parallel<T> 
```
