# Langs (Safe Embedded Languages)

# `lang` defines custom text types with automatic escaping.
lang HTML

    # Custom escaping rules can be created with `convert`
    convert(t:Text -> HTML)
        t = t.translate({"&": "&amp;", "<": "&lt;", ">": "&gt;"})
        return HTML.from_text(t)

    func paragraph(content:HTML -> HTML)
        return $HTML"<p>$content</p>"


# Type safety prevents injection:
func greet(name:HTML -> HTML)
    return $HTML"Hello $name!"

func main()

    malicious_input := "<b>hello</b>"

    safe := $HTML"User said: $malicious_input"

    assert safe == ???

    assert safe.paragraph() == ???

    greeting := greet(malicious_input)  # This won't compile