# DPiBody::not-a-desc


**Key:** `DPiBody::not-a-desc`

**Category:** description · **Severity:** error

**Source:** [`src/diag/hints.nix:850`](https://github.com/kleisli-io/nix-effects/blob/main/src/diag/hints.nix#L850)

the body of `pi` must produce a description for each input, not a plain term. Return a Desc I via `descRet`, `descArg`, `descRec`, `descPi`, or `descPlus`.

## Example

`Hint::DPiBody::not-a-desc` means the `DPiBody` position uses an ordinary term where the checker needs a Desc. The example shows the failing form first, then one way to give the checker the missing structure.

```nix
# Bad: the dependent body returns a term.
descPi nat f (_: natLit 0)

# Better: the dependent body returns a Desc.
descPi nat f (_: descRet tt)

```


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