I think the combination of "simple universal syntax" and "utility to human brains to write programs" is indeed probably a relatively small space. This is in co

I think the combination of "simple universal syntax" and "utility to human brains to write programs" is indeed probably a relatively small space. This is in contrast to simply having a "simple universal syntax", and I don't know how many solutions that may have in the abstract sense. There are many cellular automata that from a certain point of view have "simple syntax" (at least in the sense of a limited number of symbols and super limited number of ways to put them together) and have universal computation powers, but are not useful in the slightest for human programming. (Not the most common Turing tarpit to get caught in, but this has snared a number of people over the years trying to turn cellular automata into programming languages.) Who knows what other exotic possibilities may lie out there in math space where no human mind has yet even peered. I think there's probably a lot of other things that are mathematically universal computers, but like cellular automata are just too unstable (in the mathematical sense, all small changes to program produce huge changes to output; we humans prefer languages that have that characteristic only in controlled and limited ways) for humans to program. And dropping the other criterion of "simple universal syntax" of course reveals a rich space of possibilities, notably including every other programming language that isn't Lisp/Forth/Haskell-esque in theoretically being one of the simple universal syntaxes lifted up to being a programming language. (Haskell is one of the other ones, BTW, being "lambda calculus" reasonably translated to a programming language. It isn't purely so but generally neither is a Lisp.)