Я ☞ Operators ☞ yo

Precedence: 8

`yo` - [Y]oneda c[O]variant

How to read: modify argument covariantly.

Looks like a circle with a bullet point inside. This bullet point represents covariant position of a parameter we are going to map.

`yo` : t a `AR_` into (from a o) (t o)

You can think this operation as you have a container with values and you can change these values individually applying one universal function to all of them.

Some 0 `yo` Some `AR__` Some (Some 0)
  None `yo` Some `AR__` None