Past exam of the year 1 of the computer science course of the University of Oxford / 2017 / Functional programming, design and analysis of algorithms / 2 / c / Solution

The first six shared values are [1,2,3,4,5,6]. At the logical merge frontier after emitting six, the streams have these consumed prefixes and next candidates:

Each row points into the same underlying lazy list, rather than recomputing an independent copy. The inner merge supplies the union of the last two rows, and the outer merge combines it with the first. Equal candidates at six advance both supplying streams. These next candidates describe the logical frontier: a demand such as take 6 hamming need not already have evaluated their numeric values.