> For the complete documentation index, see [llms.txt](https://osl.mistium.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://osl.mistium.com/functions-and-classes/lambda.md).

# Lambda

### Example

Here's a basic example of a lambda function that adds two numbers:

```javascript
(x, y) -> (x + y)

```

## Syntax

Lambda functions are defined using the following syntax:

```javascript
// Usage example:
add = (x, y) -> (x + y)

result = add(5, 3)  // returns 8
```

The syntax consists of the following parts:

1. **Parameters**: The input parameters are enclosed in parentheses.
2. **Arrow**: The arrow `->` separates the parameters from the function body.
3. **Body**: The function body is enclosed in parentheses.

## Return Value

The return value of a lambda function is the result of the expression in the function body.

## Single input lambda functions

If a lambda function has only one input parameter, the parentheses around the parameter can be omitted.

```javascript
square = v -> (v * v)

result =  square(5)  // returns 25
```

## Typed lambda functions

Parameters can be given types, and a return type can be written between the parameter list and the arrow. Untyped parameters and return values default to `any`.

```javascript
double = (number x) number -> x * 2

double(3)  // returns 6

add = (number x, number y) -> x + y

add(1, 2)  // returns 3
```

Typed lambdas (and typed named functions) can be passed anywhere a function is expected, including array methods:

```javascript
[1, 2, 3].map((number x) number -> x * 2)  // returns [2, 4, 6]
[1, 2, 3].filter((number x) -> x > 1)      // returns [2, 3]
```