# AUR0107

## Error Message

`AUR0107: Ast eval error: expression is not a function.`

## Description

This error occurs when an expression is invoked like a function (for example `foo()`) but the resolved value is not callable.

## Solution

* Ensure the referenced member is a function.
* If it might be undefined at first, guard access (or initialize it).

## More Information

This code is also documented under the runtime-html section: [AUR0107](https://docs.aurelia.io/developer-guides/error-messages/runtime-html/aur0107).