Oh, I see! That makes sense. Thanks! On Tuesday, November 14, 2017 at 10:45:30 AM UTC-6, Seth Verrinder wrote: > > I took part of the goal to be that specs themselves would remain > compatible, so an old set of specs wouldn't start failing on data that > conforms to a new but compatible set of specs. That sort of compatibility > isn't possible when you go from disallowing something to allowing it. > > On Tuesday, November 14, 2017 at 10:15:23 AM UTC-6, Eric Normand wrote: >> >> Hey everybody! >> >> I'm chiming in after seeing this linked to in The Repl ( >> https://therepl.net/). >> >> On Alex's suggestion, I rewatched Spec-ulation last night. The parts >> about negation and evolution are towards the end. I was struck (once again) >> by how clearly he picked apart changes. Relaxing a requirement is growth. >> And adding requirements is breakage. But it left me with a question: >> >> Isn't disallowing a key and then allowing it (as optional) growth >> (instead of breakage)? All of the old clients are still fine, and new >> clients can use the key if they choose. You're relaxing the requirements. >> Taking the opposite approach, I require some keys plus allow anything else. >> Some clients will inevitably send me something with extra keys, which is >> okay, they pass my specs. Later, I add in an optional key with a defined >> spec. So I'm now restricting what used to be completely open. Isn't that >> breakage? I feel like I'm seeing it exactly opposite as Rich Hickey. He >> says if you disallow things, it's forever, because if you need to allow it >> later, that's breakage. But there's not enough explanation for me to >> understand. It seems like relaxing requirements. I feel like I'm missing >> something. In short: why is it forever? >> >> He does mention is that logic engines don't have negation. Does this hint >> that we will want to be using logic engines to reason over our specs? >> >> Thanks >> Eric >> >
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