---
title: "Read a conflict error"
description: "What a conflict message names, in what order, and how to tell a conflict from an unresolved path."
source: "https://aontu.dev/how-to/read-a-conflict-error/"
---

# Read a conflict error

What a conflict message names, in what order, and how to tell a conflict from an unresolved path.

Rendered from [`docs/how-to/read-a-conflict-error.md`](https://github.com/aontu-lang/aontu/blob/main/docs/how-to/read-a-conflict-error.md) in the engine repository, where a correction belongs, and where the test suite executes every example on this page.

A conflict message names both operands, and it pays to know which is which. For two plain facts [meeting](https://aontu.dev/docs/unification) at a path, the later-in-source one is named first:

```plaintext
Cannot unify value: 2 with value: 1
```

means two facts reached the same path (`1` earlier, `2` later) and they cannot both hold. To see everything the engine prints around that line, write `clash.aon`:

```aontu
a: b: 1
a: b: 2
```

```sh
$ aontu clash.aon
[aontu/scalar_value]: Cannot unify values at path $.a.b
...
 Cannot unify value: 2 with value: 1
  --> clash.aon:2:7
...
 Cannot unify value: 1 with value: 2
  --> clash.aon:1:7
...
$ echo $?
1
```

Read it top to bottom. The `[aontu/scalar_value]` line carries the error code and the path; a hint block restates the rule that was broken; then each operand appears with an annotated source frame: file, line, column, and the offending text with a caret under it. Note the path: a nested conflict reports the leaf values that clashed, so `a:b:1` against `a:b:2` is that same one-line message at `$.a.b`, not a complaint about `a`.

Where the conflict is reached through a disjunction, a list spread or a reference, both operands are still named but the ordering heuristic no longer applies: the value “later in source” may have travelled. Trust the two source frames, not the order.

An unresolved path is a different failure, with a different code:

```plaintext
[aontu/no_path]: Cannot resolve value at path $.x
```

Nothing contradicted anything; a `$.reference` names a key the document does not have. (An undefined `$name` variable is `[aontu/unknown_var]`, a third case: see [inject host values](https://aontu.dev/how-to/inject-host-values).)

The error codes, spelled as they render, are catalogued in the language reference under [Errors](https://aontu.dev/docs/reference-language#errors). To see every contribution that met at a path (including the ones that agreed), [explain a value](https://aontu.dev/how-to/explain-a-value); to gather every failure in one pass instead of reading them one throw at a time, [collect errors](https://aontu.dev/how-to/collect-errors).