# Motive.PiDom::not-a-type


**Key:** `Motive.PiDom::not-a-type`

**Category:** sort · **Severity:** error

**Source:** [`src/diag/hints.nix:931`](https://github.com/kleisli-io/nix-effects/blob/main/src/diag/hints.nix#L931)

the motive's domain must be a type (live in some U(k)). The motive receives the scrutinee's type as its domain and returns a type; supply a concrete type such as `nat`, `u 0`, or the datatype being eliminated.

## Example

`Hint::Motive.PiDom::not-a-type` means the `PiDom` position under `Motive` uses a term or value where the checker needs a type. The example shows the failing form first, then one way to give the checker the missing structure.

```nix
# Bad: the motive's Pi domain is a term.
motive = pi (natLit 0) (_: u 0)

# Better: the motive's Pi domain is a type.
motive = pi nat (_: u 0)

```


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