# Motive::not-a-function


**Key:** `Motive::not-a-function`

**Category:** arity · **Severity:** error

**Source:** [`src/diag/hints.nix:868`](https://github.com/kleisli-io/nix-effects/blob/main/src/diag/hints.nix#L868)

the motive must be a function from the scrutinee's type into a type, not a bare type or value. Supply a one-argument function whose body lives in some `U k`.

## Example

`Hint::Motive::not-a-function` means the `Motive` position uses a non-function where the checker needs a Pi-typed term. The example shows the failing form first, then one way to give the checker the missing structure.

```nix
# Bad: an eliminator motive is a bare type.
natElim nat zero succCase n

# Better: make the motive a function from the scrutinee.
natElim (x: nat) zero succCase n

```


---

[← All diagnostic hints](/nix-effects/diag-hints)