# E4027

Unused type parameter.

## Erroneous Example

```moonbit
fn id[T](a: Int) -> Int { a }
```

The example above declares a type parameter `T` in the identity function `id`,
however `T` is not used anywhere in the function signature,
giving the following error on line 1:

```
Unused type parameter 'T'
```

## Suggestion

Make sure the type parameter is used in the function signature:

```{literalinclude} /sources/error_codes/E4027_fixed/top.mbt
:language: moonbit
```