Add tests for infinite looping by writing code that times out

[masak]

First I was going to suggest modifying the interpreter to have a "fuel" counter (in the style of some contemporary "smart contract" evaluators), but then I realized that this can probably be expressed in pure Bel, using threads and a modicum of cleverness. Stay tuned.

A lot of functions are susceptible to infinite looping when fed cyclic lists. We should give each of them a test.

[masak]

[...] but then I realized that this can probably be expressed in pure Bel, using threads and a modicum of cleverness. Stay tuned.

Here's the general principle, nicely formatted for readability:

> (do
    (set aborted nil)
    (thread
      (let n 0
        (while (< (++ n) 5))
        (set aborted t)
        (pr 'aborted \lf)))
    ; meanwhile, in the main thread...
    (let n 0
      (while (and (no aborted)
                  (< (++ n) 1000))
        (prn n))))
1
2
3
4
aborted
5
nil

[masak]

> (do
    (set aborted nil)
    (thread
      (do
        (repeat 20)
        (set aborted t)))
    ; meanwhile, in the main thread
    (catch
      (let n 0
        (while (< (++ n) 1000)
          (if aborted (throw 'aborted))
          (prn n)))))
1
2
3
4
5
6
aborted

[masak]

I just got a better idea — which I added to the (private) bel-masak-prelude repo as bind-fn/call-limit and bind-fn/timeout.

It would be sweet to be able to use those functions in the tests. I guess in the short term it will be easier to declare them in the test file.