There are many comments discussing whether length should be unsigned or signed. There are arguments for and against it. This a prototypical carpet bump, you squ

There are many comments discussing whether length should be unsigned or signed. There are arguments for and against it. This a prototypical carpet bump, you squash it in one place it raises its head somewhere else. I see it not as a question whether lengths should be signed or unsigned but whether subtraction, assignment etc should be polymorphic w.r.t signed and unsigned. I think the issue here is the polymorphic variants of these binary operators are inherently risky. Casting gets a little tedious, but languages that do not have operator overloading should disallow subtraction from unsigned and subtraction that return unsigned. You either cast it up, or if possible reorder the expression/comparison so that the problem goes away. Even assignment can be a problem. Ocaml can get irritating because it takes this view but I think it is safer this way. It is very hard to be always vigilant about the unsigned signed issue, but hopefully a compiler error will mitigate risks, not completely, but it is better than nothing. That leaves languages that allow operator overloading, in those cases if you are overloading an operator you better know what you are doing, and watch out for cases where the operator is not closed.