When working with Unison code, you might encounter the followingoperatorswhich are provided by the`base`

library. They are commonly used for manipulating the order in which a function is applied to its arguments.

`a``<<`

b

`<<`

b`<< : (b ->{𝕖} c) -> (a ->{𝕖} b) -> a ->{𝕖} c`

`<<`

,also known as "compose," takes in two functions`b -> c`

and`a -> b`

and returns a function from`a -> c`

.

Piping multiple functions together with the compose operator looks like:

`composeMultiEx : Text -> Boolean`

The expression is actually parsed:

`((Boolean.not << Nat.isEven) << Text.size)`

Giving us a function that expects`Text.size`

'sargument of`Text`

and returning the final result of applying the`not`

function.

`a``>>`

b

`>>`

b`>> : (a ->{𝕖} b) -> (b ->{𝕖} c) -> a ->{𝕖} c`

`>>`

,also known as`andThen`

,is like`compose`

with the function argument order reversed. It takes in two functions`a->b`

and`b->c`

and returns a function from`a->c`

.

Piping together multiple`>>`

calls looks like:

`a``|>`

b

`|>`

b`|> : a -> (a ->{𝕖} b) ->{𝕖} b`

While`>>`

returns a function,`|>`

allows us to apply an argument to a function, returning the value of that function call. When using`|>`

it's helpful to remember that the function argument should be on theleft handside of the operator. The value of this operator might not be immediately obvious--after all, why use special operators for function application when parentheses will suffice 🤔--but you'll often see multiple instances of the`|>`

operator chained together to form a complete expression.

```
pipeRightEx : Optional Nat
pipeRightEx =
use Nat +
Some 5 |> Optional.filter Nat.isEven |> Optional.map (n -> n + 1)
```

You might find that there's a greater fit between the semantic order of this expression and the order in which the function calls are applied than in the non`|>`

version of this expression:

```
pipeEx : Boolean
pipeEx = isSome (Optional.filter Nat.isEven (Some 5))
```

`a``<|`

b

`<|`

b`<| : (a ->{𝕖} b) -> a ->{𝕖} b`

When using`<|`

,the function should be on the left hand side of the operator with the function's argument on the right hand side. You can read the`<|`

operator as "pipe backwards." You might choose to use this operator when the argument to the function in question needs some "pre-processing" which would otherwise involve parentheses.

```
pipeBackwardsEx : Optional Nat
pipeBackwardsEx =
Optional.filter Nat.isEven <| pipeBackwardsEx.wrap 5
```

Note that the`<|`

operator does not change the precedence of the operator function calls. The leftmost sub-expression is still executed first. You can use parentheses to change the grouping.