Bram Cohen's comment from the original Python code (with syntax changed to OCaml):
get_matching_blocks a b returns a list of triples describing matching
subsequences.
Each triple is of the form (i, j, n), and means that a <|> (i,i+n) = b <|> (j,j+n). The triples are monotonically increasing in i and in j.
The last triple is a dummy, (Array.length a, Array.length b, 0), and is the only triple with n=0.
Example:
get_matching_blocks |"a";"b";"x";"c";"d"| |"a";"b";"c";"d"|
returns
(0, 0, 2), (3, 2, 2), (5, 4, 0)