# E0291

An inherent `impl` for a prelude type, such as `impl FsRead { ... }`: only the prelude declares methods on its types. Write a free function, or implement a trait. Spans the `impl`'s type.

**Machine-applicable fix:** none.

## Example

This program fails with `E0291`.

```oska
impl FsRead {
    fn size(self) -> Int {
        1
    }
}
```

## Fixed

The same program, fixed.

```oska
fn size(fs: FsRead) -> Int {
    1
}
```

Listed in the [checker notes](/checker.md#e0291). `oskac explain E0291` prints this entry offline.