# V2002 arity_mismatch

URL: /docs/errors/V2002
Markdown: /docs/errors/V2002.md

> A function was called with the wrong number of arguments, or a pattern has the wrong number of fields.

An error from the `type` phase. `sakura explain V2002` prints this explanation offline.

A function was called with the wrong number of arguments, or a pattern has the wrong number of
fields. The diagnostic's `expected` and `actual` carry both counts; arguments are positional, with
no defaults (pass a record when a call needs options).

Wrong:

```sakura
fn double(x: Int) -> Int { x * 2 }
fn four() -> Int { double(2, 2) }
```

Fixed:

```sakura
fn four() -> Int { double(2) }
```

## Wrong program [#wrong-program]

[`compiler/tests/ui/V2002_arity_mismatch.sakura`](https://github.com/icantcodefyi/sakuralang/blob/master/compiler/tests/ui/V2002_arity_mismatch.sakura), which the compiler's ui suite runs through `sakura check`:

```sakura
fn double(x: Int) -> Int { x * 2 }

fn four() -> Int { double(2, 2) }
```

`sakura check --json` reports this record (pretty-printed; `$DIR` is the fixture's directory):

```json
{
  "schema_version": "1.0",
  "kind": "diagnostic",
  "id": "d:61ad7e6f1b4ce063",
  "code": "V2002",
  "severity": "error",
  "phase": "type",
  "message": "this call passes 2 arguments to a function of type `fn(Int) -> Int`, which takes 1",
  "snapshot": "sha256:$SNAPSHOT",
  "symbol_id": "main::V2002_arity_mismatch::four",
  "spans": [
    {
      "uri": "file://$DIR/V2002_arity_mismatch.sakura",
      "content_hash": "sha256:c871525ab5c724ef81dd0f38e0dad00386ca60537d36d8e833a2e8bfe7e61031",
      "start_byte": 89,
      "end_byte": 101,
      "role": "primary"
    }
  ],
  "related_ids": [],
  "expected": null,
  "actual": null,
  "obligation": null,
  "counterexample": null,
  "explanation_uri": "sakura://explain/V2002",
  "fixes": []
}
```

More fixtures for this code: [`compiler/tests/ui/V2002_row_argument_count.sakura`](https://github.com/icantcodefyi/sakuralang/blob/master/compiler/tests/ui/V2002_row_argument_count.sakura).

## Fixed program [#fixed-program]

[`compiler/tests/ui/V2002_arity_mismatch.fixed.sakura`](https://github.com/icantcodefyi/sakuralang/blob/master/compiler/tests/ui/V2002_arity_mismatch.fixed.sakura), which `sakura check` accepts with no diagnostics:

```sakura
fn double(x: Int) -> Int { x * 2 }

fn four() -> Int { double(2) }
```