@chi It’s a bit of a different approach, but something like this might work well:

private enum class NestingCharacters(val open: String, val close: String) {
    BRACE("{", "}"),
    PAREN("(", ")"),
    BRACKET("[", "]");

    fun apply(char: String, stack: Stack<String>) {
        when (char) {
            open  -> stack.push(char)
            close -> {
                val top = stack.peek()
                if (stack.isStackEmpty()) throw SyntaxErrorTwoException(char)
                if (top == open) stack.pop() else throw SyntaxErrorThreeException(top, char)
            }
        }
    }
}

fun linter2(line: String): Boolean {
    with(Stack<String>()) {
        line.split("").forEach { char ->
            NestingCharacters.values().forEach { it.apply(char, this) }
        }
        
        if (isNotEmpty()) throw SyntaxErrorOneException(peek())
    }
    return true
}

Thanks! Would look at it

They’re just part of that

enum

, so that’s the full definition in the code listing above.