# E4021

The value identifier is unbound.

## Erroneous Example

```{literalinclude} /sources/error_codes/4021_error/top.mbt
:language: moonbit
```

The example above tries to call the function `to_integer` in a package `@bool`,
but this function is not present in the package `@bool`,
giving the following error on line 1:

```
Value to_integer not found in package `bool`.
```

## Suggestion

Make sure the identifier is correct.

In the above example, the method name should be `to_int` instead of
`to_integer`:

```{literalinclude} /sources/error_codes/4021_fixed/top.mbt
:language: moonbit
```