# ::unhandled-boot-inl


**Key:** `::unhandled-boot-inl`

**Category:** shape · **Severity:** error

**Source:** [`src/diag/hints.nix:945`](https://github.com/kleisli-io/nix-effects/blob/main/src/diag/hints.nix#L945)

the left injection `inl x` has no inference rule — the sum type's right summand is not determined by the syntax of `x` alone. Annotate with `ann (inl x) (sum A B)` to fix the expected sum, or place it where checking already provides one.

## Example

`Hint::unhandled-boot-inl` means `inl` is in inference mode without an expected Sum type. The example shows the failing form first, then one way to give the checker the missing structure.

```nix
# Bad: inl does not determine the right summand by itself.
infer emptyCtx (inl (natLit 1))

# Better: annotate the intended sum type.
infer emptyCtx (ann (inl (natLit 1)) (sum nat bool))

```


---

[← All diagnostic hints](/nix-effects/diag-hints)