x = '0'
function start ()
    return function () end
end

function set_x (v)
    x = v
    return function () end
end

function if_x (v)
    if x == v then
        print ("x = ", v)
        return function (block) block[1]() end
    else
        print ("x != ", v)
        return function () end
    end 
end

-- DSL here
start {
    set_x '10',
    if_x '10' { function() print ('x is 10') end },
    if_x '20' { function() print ('x is 20') end }
}