Now this sounds very dangerous - one of big problems of declarative style is that it's too easy to accidentally build a system that does much more than you intended, totally killing performance.

There is a very, very big difference between running a search once and re-running it whenever search changes; if you want it one way then you definitely don't want it the other way and that would be a serious problem.

That's not a "in this language" issue, you can do both ways in any language, but this choice you made should be (a) explicit and (b) obvious, which it doesn't seem to be in this case; where a reader can reasonably expect the search to be run once.