# DPlusR::not-a-desc


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

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

**Source:** [`src/diag/hints.nix:878`](https://github.com/kleisli-io/nix-effects/blob/main/src/diag/hints.nix#L878)

the right summand of `plus` must be a description at the same index type as the left summand

## Example

`Hint::DPlusR::not-a-desc` means the `DPlusR` 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 right summand is not a description.
descPlus leftDesc (natLit 0)

# Better: both summands are descriptions.
descPlus leftDesc (descRet tt)

```


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