I have used APL and k, and tried to use J; somehow J never clicked properly. APL mostly did, but k perfectly did. Conceptually, they are more similar than they

I have used APL and k, and tried to use J; somehow J never clicked properly. APL mostly did, but k perfectly did. Conceptually, they are more similar than they are distinct - but k is tiny and more practical, and IIRC even Iverson said that in retrospect, most choices where k differs from J (juxtaposition vs. trains and hooks; reduction going l->r instead of r->l), the choices whitney made in k are clearer and more useful even if they aren't as pure and consistent.