# LevelSucPred::type-mismatch


**Key:** `LevelSucPred::type-mismatch`

**Category:** universe · **Severity:** error

**Source:** [`src/diag/hints.nix:920`](https://github.com/kleisli-io/nix-effects/blob/main/src/diag/hints.nix#L920)

the predecessor of `suc` must be a Level

## Example

`Hint::LevelSucPred::type-mismatch` means the `LevelSucPred` position supplies a term whose type does not match the expected type. The example shows the failing form first, then one way to give the checker the missing structure.

```nix
# Bad: suc expects a Level.
levelSuc nat

# Better: pass a level expression.
levelSuc level0

```


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