# E4215

Compiler diagnostic name: `expect_template_string`.

Template writing expects a string template.

The `<+` template-writing operator writes a string template to the value on its
left. The right-hand side must be a string literal, an interpolated string, or a
multiline string template. Other expressions cannot be expanded as template
content.

## Erroneous example

```moonbit
writer <+ 1
```

The right-hand side is an integer, not a template string.

## Suggestion

Use a string template on the right-hand side.

```moonbit
writer <+ "1"
```