Hi, Thanks for the suggestions. A few more questions. The (<<*>>) function is just one of a number of lazy matrix arithmetic functions that I have. If I need them to be evaluated strictly, is it best to modify the matrix code, or the code that's calling it? In this case, it looks like I can fix the problem by modifying the calling code. For example: test3 = iterate' (\m -> sum (map last m) `seq` m <<*>> id3) id3 !! 1000000 This works fine with the *unmodified* version of (<<*>>). However, note that I've had to do some unnecessary work - sum (map last m). Is there a better way? Or, is it better to modify the matrix code itself? Perhaps there's an argument that matrix arithmetic should be strict - after all, integer arithmetic is strict. But it seems potentially useful to have at least (<<+>>) as lazy, so that I can add together infinite matrices. Which is best? Thanks in advance.