Coffeescript：无与伦比的突出错误

Question

以下代码：

binary_search = (arr, val)->
    arr = arr.concat(arr)
    lower = 0 ; upper = arr.length-1
    while upper-lower > 1
        mid = Math.floor((lower+upper)/2)
        if arr[mid] is val
            return mid
        if arr[mid] < val
            if arr[mid-1] < arr[mid+1]
                low = mid+1
            else 
                up = mid-1
        else
            if arr[[mid-1] > arr[mid+1]
                low = mid+1
            else 
                up = mid-1
    return -1

and get the following error:

   error: unmatched OUTDENT
            up = mid-1

我做错了什么？