NoTempDSL.kt

inline class AppendScope(val appendable: Appendable) {
    inline fun indent(indent: Int = 4, body: IndentScope.() -> Unit) {
        IndentScope(indent).body()
    }
}
inline fun AppendScope.appendln(value: CharSequence) = appendable.appendln(value)

inline class IndentScope(val indent: Int = 4) {
    inline fun AppendScope.appendln(value: CharSequence) = appendable.append(" ".repeat(indent)).appendln(value)

    inline fun indent(indent: Int = 4, body: IndentScope.() -> Unit) {
        IndentScope(this.indent + indent).body()
    }
}

inline fun prettyPrintTo(appendable: Appendable, body: AppendScope.() -> Unit) {
    AppendScope(appendable).body()
}

fun main() {

    val sb = StringBuilder()
    prettyPrintTo(sb) {
        appendln("fun foo() {")
        indent {
            appendln("val x = 2")
            appendln("val y = 3")
            appendln("run {")
            indent(4) {
                appendln("println(\"x = \$x\")")
            }
            appendln("}")
            appendln("return x * y")
        }
        appendln("}")
    }

    println(sb)
}