[Question] Any side effect function in TaskEither or Either?

[samuelyung]

Hi, I come from Java (vavr) and for the side effect function I mean something like peek(), that is, just peek without changing Right if it's a Right, and for Left it is called peekLeft().

Now I need to do something like this to simulate peek:

taskEither.map((right) {
  doSomething(right);
  return right;
})

[SandroMaglione]

Hi @samuelyung

I think what you are looking for is chainFirst.

[samuelyung]

No...

chainFirst() requires a function argument having a return type of TaskEither<L, C>, while the peek()'s Consumer argument doesn't return anything.
That is, it just "observe" the value.

[SandroMaglione]

You can return a TaskEither with return type as void. When chainFirst is executed the result is ignored, so in practice it works as if you are observing the value