I have these three in my list, and one more: APL (or J or K -- especially K) Scheme/Lisp is about how data and code are equivalent in a practical sense. I'm n

I have these three in my list, and one more: APL (or J or K -- especially K) Scheme/Lisp is about how data and code are equivalent in a practical sense. I'm not sure how I would describe Prolog in a single sentence - it's about using a powerful concept (Unification) as a base of computation - it makes a lot of logic programming simple (and unfortunately, it makes some simple iteration complicated). Forth is an exercise in minimalism and blurring (or actually removing) the line between compiling, interpreting, parsing. I wouldn't treat Forth and Factor equivalently - Factor borrows Forth's concatenativeness, but it is very far from Forth's minimalism. K is an exercise in choosing the minimal set of operators and functions that would produce very terse programs that need much less abstraction, without having to compromise on speed. Unlike Lisp and Forth, the base K has some 50-100 mostly orthogonal operators (depending on how you count) that work together to give you a lot without forcing you to abstract.