Why monads and not something else? Because monads appear to be a/the mathematical structure underlying the denotation of programs with effects. Why that type s

Why monads and not something else? Because monads appear to be a/the mathematical structure underlying the denotation of programs with effects. Why that type signature? You only have two options: that, or m (m a) -> m a. The former is more popular for ergonomic reasons mostly. It doesn’t really matter.