[kelseyfrog]

Most of these issues are a consequence of recursion never getting the same codification as the rest of the jmp patterns we eventually turned into control structures - eg: if, for, while, try/catch.

In the meantime, the theory of structured recursion[recursion schemes] has been developing, yet no language offers then as first class constructs. The best we get is library support. Imagine if we had to import a package to support if statements. The result? Programmers write recursive programs while navigating all the foot guns described in the article. No wonder recursion is hard to get right.

[n0blenote]

I might not be understanding what you’re saying here… but recursion compared to your if/whiles, are inherently coupled to the shape of the type they traverse where in the prior two we define data comparisons or input sizes.

Using a jmp isn’t really a call as you’d know, and information is lost that would be crucial to unwinding a recursion.

A recurse keyword would still leave the person writing the code with the decision with proving termination with base cases or trampolines — lest there is just a bunch of math that would unwind your recursion into a better bounded problem. Which is kind of what current keywords do anyway.

[kelseyfrog]

You're absolutely right. Recursion is tied to the shape of the data being recursed. It can be expressed a number of ways, but generally having a functor for the data type gives a lot of milage in operating over it. See https://github.com/passy/awesome-recursion-schemes for more of what I'm getting after.

[Jhsto]

I've been writing a language around recursion schemes! Insofar it's just a library for Lean, but I wish to one day release it as an array programming language. I'm submitting a thesis in ~3 months, after which I'll be open-sourcing it.