# DPlusL::not-a-desc


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

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

**Source:** [`src/diag/hints.nix:876`](https://github.com/kleisli-io/nix-effects/blob/main/src/diag/hints.nix#L876)

the left summand of `plus` must be a description (Desc I)

## Example

`Hint::DPlusL::not-a-desc` means the `DPlusL` 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 left summand is not a description.
descPlus (natLit 0) rightDesc

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

```


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