procedure binsearch(A, target)
    if *A = 0 then fail
    mid := *A/2 + 1
    if target > A[mid] then {
        return mid + binsearch(A[(mid+1):0], target)
        }
    else if target < A[mid] then {
        return binsearch(A[1+:(mid-1)], target)
        }
    return mid
end