On The Willows Letra

Required
Of us songs
And our tormentors mirth
On the willows, there
We hung up our lives
For our captors there
Required
Of us songs
And our tormentor's mirth
Saying
Sing us one
Of the songs of Zion
Sing us one
Of the songs of Zion
But how can we sing?
Sing the Lord's songs?
In a foreign land?