# E4108

The loop is expected to yield a value; in current syntax, add a `nobreak`
branch.

This error occurs when the compiler infers that a for-loop is expected to yield
a non-Unit value based on its context (such as the function's return type), but
the loop lacks a branch to provide that value. In current MoonBit syntax, that
branch is written as `nobreak`.

In MoonBit, when a for-loop is used in a context where a value is expected (for
example, when the function returns a non-Unit type), the loop must have an
`nobreak` branch that specifies what value to return when the loop completes
normally. This is because:

1. The loop body itself cannot yield a value (unlike `loop` expressions)
2. Without a `nobreak` branch, there's no way to determine what value should be
   returned when the loop finishes without breaking

This commonly occurs in two situations:

- When the for-loop is the last expression in a function that returns a non-Unit
  type
- When the for-loop's result is assigned to a variable or used in an expression
  that expects a non-Unit value

## Erroneous example

```{literalinclude} /sources/error_codes/4108_error/top.mbt
:language: moonbit
```

## Suggestion

To fix this error, you can:

- add a `nobreak` branch to the for-loop:

```{literalinclude} /sources/error_codes/4108_fixed/top.mbt
:language: moonbit
```

- change the function's return type to `Unit` if you don't need to return a value
  from the loop:

```{literalinclude} /sources/error_codes/4108_fixed/top_1.mbt
:language: moonbit
```