Subtypes: Automation, Reference.
One of the basic building block of Я - function.
You can use its type alias (AR) for good looking infix type operator:
(a `AR` o) ~ (AR a o)
(a `AR_` o) ~ (AR_ a o)
(a `AR__` o) ~ (AR__ a o)
(a `AR___` o) ~ (AR___ a o)
(a `AR____` o) ~ (AR____ a o)
(a `AR_____` o) ~ (AR_____ a o)
(a `AR______` o) ~ (AR______ a o)You can map input contravariantly:
… and output covariantly):