# E4159

Implementations are missing.

When a package implements a
[virtual package](/toolchain/moon/package.md#virtual-package), it is checked
against the interface of that virtual package, and this error is emitted if some
of the interface is missing.

## Erroneous example

```{literalinclude} /sources/error_codes/4159_error/E4159.mbti
:language: moonbit
:caption: E4159.mbti
```

```{literalinclude} /sources/error_codes/4159_error/top.mbt
:language: moonbit
:caption: top.mbt
```

## Suggestion

Implement the missing implementations and fulfill the interface. Make sure that
the expected definitions are indeed public.

```{literalinclude} /sources/error_codes/4159_fixed/top.mbt
:language: moonbit
```