wren ng thornton wrote:
I have long been disappointed by a number of `error`s which shouldn't be. For example, the fact that `head` and `div` are not total strikes me as a (solvable) weakness of type checking, rather than things that should occur as programmer errors/exceptions at runtime. The use of `error` in these cases muddies the waters and leads to a laissez-faire attitude about when it's acceptable to throw one's hands up in despair and use `error` rather than writing a better function.
head uses "error" in precisely the correct, intended fashion. head has a precondition (only call on non-empty lists) and the "error" is just there to give you some hint that you made a mistake - got the precondition wrong. It's certainly not intended to be catchable. And that is a correct use of error. There are programming styles which avoid using 'head'. You are free to use those if you don't like it. I myself am content to use 'head' on lists which I know are guaranteed to be non-empty. Jules