# XO0157: `${}` with no expression

An interpolation must contain an expression whose type implements `Display`. `${}` (or `${ }`) has nothing to interpolate. Put an expression inside, or escape the dollar sign (`\${}`) to write the characters literally. See core 1.6.

## Example

```xo
fn f() -> Str {
  "a ${}"
}
```

## Fix

```xo
fn f() -> Str {
  "a \${}"
}
```

Run `xo explain XO0157` for this text in a terminal, or see
[section 10.6 of the specification](../../spec/core/#106-diagnostic-codes).