Markov Chain generator

As it turns out, with a sufficiently dense input text, a Markov Chain generator is actually reasonably easy to implement.

From page 62 of The Practice of Programming:

set w1 and w2 to the first two words in the text

print w1 and w2

loop:

randomly choose w3, one of the successors of prefix w1 w2 in the text
print w3
print w1 and w2 by w2 and w3
repeat loop