# E4133

This `for .. in` loop has incorrect number of loop variables.

MoonBit supports only one or two loop variables in `for .. in` loop.

- One loop variable is used for the content of the iterable.
- Two loop variables are used for the index and the content of the iterable
  respectively.

## Erroneous example

```{literalinclude} /sources/error_codes/4133_error/top.mbt
:language: moonbit
```

## Suggestion

If you want to iterate over the index and the content of the iterable, you can
use two loop variables:

```{literalinclude} /sources/error_codes/4133_fixed/top.mbt
:language: moonbit
```

If you want to iterate over a iterable of tuples, then you need to explicitly
destructure the tuple inside the loop body:

```{literalinclude} /sources/error_codes/4133_fixed/top_1.mbt
:language: moonbit
```