(cc:ak) Okay, this sounds just crushingly obvious now that I say it, but honestly, I don’t think it’s occurred to me:
One reason that equality is such a nightmare in Java and Python (which turns out to be JUST AS BAD), is that those of us that actually want to write unit test cases want *intensional* equality, not extensional equality—but not pointer-based equality. I just came across a nice example while working on code for first-year students (thanks, Aaron!). Specifically, imagine an “array” class that contains a backing array and a length, where the backing array might be arbitrarily longer than the length: (struct arr (vec len)) So, for instance, an array with two elements in it might be represented as either (arr (vector “apple" “horse” #f #f #f) 2) or as (arr (vector “apple” “horse” #f) 2) —they both represent the array of length 2 that has “apple” as the first element, and “horse” as the second. If I’m providing this library to be used by others, I probably want extensional equality; I don’t want users of my library to be able to distinguish between the two. However, if I’m writing unit tests for my library, I definitely *do* want to be able to distinguish between the two, for instance in checking the behavior of arrays that fill up and need to be resized. Moreover, pointer-based equality—the == of Java, and the `is` of Python (IIUC)—is also largely useless for unit tests. It’s probably not terribly controversial to suggest that neither Python nor Java were designed with unit testing in mind. Accordingly, I shouldn’t be surprised to discover that they don’t provide a natural notion of equality that fits well with unit tests. So, I have three questions: 1) Is there an existing term for what I would call “functional extensional equality”—that is, Racket’s ‘equal?’ ? 2) Does what I wrote make sense? 3) Has this been written down somewhere else, as part of a larger work? Thanks, everyone! John -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.