To expand on this a little: J was what Iverson did after APL. ('arcfide has called it a "stopgap," but I don't think that's right: it does a lot of things bett

To expand on this a little: J was what Iverson did after APL. ('arcfide has called it a "stopgap," but I don't think that's right: it does a lot of things better than even Dyalog does.) In that way, it's a bit more pure of an experience [compared to Dyalog APL], and in a way brings the notation a lot further, as long as you can ignore the ASCIIfication of it. k was made explicitly as a stripped-down version of (primitive-)APL. This has many trade-offs. It does make performance optimizations a lot easier (which is partially why practically every non-toy k implementation is faster than Dyalog, which is fast in its own right, even if J is usually faster). It's also mildly easier to keep in one's head in most cases. It's a lot more mainstream in comparison to J, both because of the performance optimizations and because it's a lot less of a leap from Lisp to k than it is from Lisp to J. If I remember correctly, Arthur is a bit more of a normal person on this: he prefers/preferred writing Lisp to APL, and k is definitely a lot easier to compare to conventional languages than J or APL. J was designed as a way to spread notation to the masses, k was designed as a way to get incredibly small amounts of code to do very big things. Both are good at both, I think, though to varying degrees. k, though, appeals to a core aspect of the programmer by design: small. And it's small in a way that can't be called code golfing, either, which is like cocaine to your average programmer. It's primitive, very shiny, and its bite-sizedness appeals to your average cascade of attention-deficit (mostly grown-up now) teenagers that make up these sort of spaces. It's basically bait, and in a really good way. Another reason is because J doesn't have all of the cool little snippets that k people love posting; there's no "ray-tracer in 7 lines of J" text dump despite something similar being possible, just because of the community that's formed around k. In k you have a bunch of people like Stevan Apter who just live for cool programming languages. They devour that stuff and try and make the coolest things they can to show everyone.