Those annotations create a compile-time enforced typological relationship between the input and output values of the function. Python doesn't have mandatory type-checking so it can't do that. But parent wasn't referring to type-checking. They claimed monads have expressive power unavailable in other languages.
> Those annotations create a compile-time enforced typological relationship between the input and output values of the function. Python doesn't have mandatory type-checking so it can't do that
Python doesn't have (mandatory) compile time type checking, no, but in principle a dynamically typed language could still be referentially transparent, and then it would (or at least could) still be the case that the only effects that a particular operation can perform are those arguments that are passed into it.
> But parent wasn't referring to type-checking. They claimed monads have expressive power unavailable in other languages.
That's true. But think of other syntax sugar like async/await. That comes for free in Haskell with monads and do notation.
