# XO0405: type cannot be inferred here; annotate it

The checker needs a type at this point and nothing determines it yet: a closure parameter with no expected function type, a value whose method or field is used before its type is known, a `match` subject, or an iterated value. Add a type annotation to the parameter or binding. See core 3.3.

## Example

```xo
fn f() -> Int {
  let g = fn(p) { p }
  g(1)
}
```

## Fix

```xo
fn f() -> Int {
  let g = fn(p: Int) -> Int { p }
  g(1)
}
```

Run `xo explain XO0405` for this text in a terminal, or see
[section 10.6 of the specification](../../spec/core/#106-diagnostic-codes).