Arithmetic progressions make *sense* for anything that has "+", whether or not it also has "<". For my Smalltalk system, I ended up with a GenericInterval class with a creation method new: size from: start by: delta. With *that* interface, a delta of zero is perfectly harmless. GenericInterval new: 4 from: 6 by: 0 is (6 6 6 6) and of course GenericInterval new: 1 from: 6 by: 0 is (6) because the new: argument *says* there is to be 1 element. I understand why class Enum doesn't have this kind of interface. Basically, we want to compute [delta*n + start | n <- [0..size-1]] where in cases like duration*n+timestamp delta and start are not the same type. But let's face it, all that means is that if we want this kind of thing, all we have to do is roll our own arithmetic progression functions. Enum has other problems, like its coupling to Int. I find it odd that [1%1,9%8..2%1] works usefully even though fromEnum (1%1) == fromEnum (9%8) == 1. Sensible, just odd.