# XO0203: success of a Result typed T must be written Ok(x)

In a function declared `-> T ! E`, a returned `T` means success and a returned `Result[T, E]` is passed through as is. When `T` is itself a `Result`, a returned `Result` would be ambiguous, so success must be written `Ok(x)` explicitly. The same applies to closures whose results are collected, as in `xs.map(fn(x) { Ok(g()) })`. See core 2.6.

## Example

```xo
enum E { A }

fn f(r: Result[Int, Str]) -> Result[Int, Str] ! E { r }
```

## Fix

```xo
enum E { A }

fn f(r: Result[Int, Str]) -> Result[Int, Str] ! E { Ok(r) }
```

Run `xo explain XO0203` for this text in a terminal, or see
[section 10.6 of the specification](../../spec/core/#106-diagnostic-codes).