#readwise
# Kleisli Composition
## Metadata
- Author: [[Mark Seemann]]
- Full Title: Kleisli Composition
- URL: https://blog.ploeh.dk/2022/04/04/kleisli-composition/
## Highlights
- Imagine some monad - any monad. It could be *Maybe* (AKA *Option*), *Either* (AKA *Result*), *Task*, *State*, etcetera. In [Haskell](https://www.haskell.org) notation we denote it `m`. ... If we generalise this notation, we would write a monadic function like this:
`a -> m b` ... it seems intuitive that you can also compose monadic functions:
`(>=>) :: Monad m => (a -> m b) -> (b -> m c) -> a -> m c`
The [`>=>`](https://hackage.haskell.org/package/base/docs/Control-Monad.html#v:-62--61--62-) operator is known as the *fish* operator ... This is known as *Kleisli composition*. ...
```csharp
public static Func<T, Monad<T2>> Compose<T, T1, T2>(
this Func<T, Monad<T1>> action1,
Func<T1, Monad<T2>> action2)
{
return x => action1(x).SelectMany(action2);
}
```
- Notice that Kleisli composition works for any monad. You don't need any new abilities in order to compose a monad in this way. The composition exclusively relies on `SelectMany` (monadic *bind*). ([View Highlight](https://read.readwise.io/read/01gwp0na3ahf1ad5wz2f7a04rz))
- Kleisli composition lets you compose two (or more) compatible monadic functions into a single monadic function. ([View Highlight](https://read.readwise.io/read/01gwp0q0yg6d6h49jxx5c9fcvj))