What is a comonad?

What is a comonad?

Comonad is a Functor and provides duals of the Monad pure and flatMap functions. A dual to a function has the same types but the direction of the arrows are reversed. Whether or not that is useful, or even possible, depends on the particular type.

What are comonads useful for?

A comonad can be used not only to describe linear one-directional structures (streams), but also bidirectional structures, two-dimensional structures, and more. You can think of it as having one “current” value that’s easily accessible plus the whole (possibly infinite) neighborhood (or “context”).

Who invented monads?

mathematician Roger Godement
The mathematician Roger Godement was the first to formulate the concept of a monad (dubbing it a “standard construction”) in the late 1950s, though the term “monad” that came to dominate was popularized by category-theorist Saunders Mac Lane.

Are monads pure?

Monads are not considered pure or impure. They’re totally unrelated concepts. Your title is kind of like asking how verbs are considered delicious. “Monad” refers to a particular pattern of composition that can be implemented on types with certain higher-kinded type constructors.

Is monad a functor?

The first function allows to transform your input values to a set of values that our Monad can compose. The second function allows for the composition. So in conclusion, every Monad is not a Functor but uses a Functor to complete it’s purpose.

Is maybe a monad?

In FP we often loosely say things like “arrays are monads” or “maybe values are monadic” etc. However, speaking more strictly, it is not the values (like [1, 2, 3] , Nothing , or Just(6) ) that are monads, but the context (the Array or Maybe “namespace” as you put it).

What is the difference between functor and monad?

A functor takes a pure function (and a functorial value) whereas a monad takes a Kleisli arrow, i.e. a function that returns a monad (and a monadic value).

What is io Haskell?

IO is the way how Haskell differentiates between code that is referentially transparent and code that is not. IO a is the type of an IO action that returns an a . You can think of an IO action as a piece of code with some effect on the real world that waits to get executed.

What is null Haskell?

null is a function that takes a list and tells you whether or not the list is empty. Since your result is not supposed to be a function, using null as your result is a type error. The type Maybe t in Haskell has two possible values: Just x where x is of type t or Nothing .

Is a functor a Monad?

A functor is a data type that implements the Functor typeclass. A monad is a data type that implements the Monad typeclass. A Maybe implements all three, so it is a functor, an applicative, and a monad.

What is a C-section and how is it done?

What is a C-section? A cesarean delivery, also called a C-section or cesarean birth, is the surgical delivery of a baby through a surgical cut or incision in a woman’s abdomen and uterus. After the baby is removed from the womb, the uterus and abdomen are closed with stitches that later dissolve. 1

What happens if you have more than one C-section?

Women who have multiple C-sections are at increased risk of placental problems as well as heavy bleeding, which might require surgical removal of the uterus (hysterectomy). If you’re considering a planned C-section for your first delivery, work with your health care provider to make the best decision for you and your baby.

What is a cesarean section called?

This procedure is also known as a C-section, and can happen quickly based on the emergency situation. What is a cesarean section? A cesarean section, also called a C-section, is a surgical procedure performed when a vaginal delivery is not possible or safe, or when the health of the mother or the baby is at risk.

How long does it take to deliver a baby with C-section?

In some cases, the cesarean delivery will happen very quickly, with the baby being delivered in as little as 15 to 20 minutes. This is an emergency C-section. Afterwards, there will be additional time when the provider will stitch up the uterus and abdomen.