# Case::type-mismatch


**Key:** `Case::type-mismatch`

**Category:** elimination · **Severity:** error

**Source:** [`src/diag/hints.nix:910`](https://github.com/kleisli-io/nix-effects/blob/main/src/diag/hints.nix#L910)

this case-body's inferred type does not match the type the eliminator's motive requires

## Example

`Hint::Case::type-mismatch` means the `Case` 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: one case branch returns the wrong type.
caseOf scrutinee { left = x: true_; right = y: natLit 0; }

# Better: all branches return the motive's type.
caseOf scrutinee { left = x: natLit 1; right = y: natLit 0; }

```


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