> For the complete documentation index, see [llms.txt](https://fluence.gitbook.io/aqua-book/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://fluence.gitbook.io/aqua-book/language/expressions/functions.md).

# Functions

A function in Aqua is a block of code expressing a workflow, i.e., a coordination scenario that works across one or more peers.

A function may take arguments of any type and may return a value.

A function can call other functions, take functions as arguments of [arrow type](/aqua-book/language/types.md#arrow-types) and be provided as an arrow argument.

Essentially, a function is an arrow. The function call is an expression that connects named arguments to an arrow, and gives a name to the result.

Finally, all a function does is call its arguments or service functions.

```haskell
service MySrv:
  foo()

func do_something(): -- arrow of type: -> ()
  MySrv "srv id"
  MySrv.foo()
```

{% hint style="warning" %}
TODO

* list all expressions
* for each, explain the contract and provide a use case
  {% endhint %}