# `type.unary_operand`

Operator cannot be used with this value.

Area 3, [Logic](../topics/logic.md); not declinable; the next step is usually the agent's.

```jadpo
type Phrase = Text {}

type Flag = Bool {}

function negate(phrase: Phrase) -> Flag {
    return Flag(not phrase)
}
```

```text
error: `not` needs a `Bool`, and `phrase` is a `Phrase`
 --> main.jadpo:6:21
  |
6 |     return Flag(not phrase)
  |                     ^^^^^^ this is `Phrase`
  reason: `not` works on `Bool` values and types built on `Bool`; Jadpo has no truthiness.
  next: Compare `phrase` to get a `Bool` (agent)
  rule: type.unary_operand
  help: https://jadpo.dev/docs/errors/type.unary_operand

check failed: 1 error, 1 file
```