breakfrom

local top

function mklabel(name, func)
    if not top then top = func end
    local isTop = top == func
    local suc, res = pcall(func)
    if not suc then
        if not res:find("__BREAKFROM") then error(res, -1) end
        local target = res:gsub("[^\:]+:[^\:]+: __BREAKFROM", "")
        if name ~= target then
            if isTop then
                error("Tried to break from label '" .. target .. "' which does not exist.", 2)
            end
            error("__BREAKFROM" .. target)
        end
    end
    if isTop then top = nil end
end

function breakfrom(name)
    error("__BREAKFROM" .. name)
end