aoc2018 | Rust solutions to the Advent Of Code | Learning library

Confirmed that this works (with tail recursion) under 9.9, with or without bytecode generation enabled, but under 9.8 it succeeds only if bytecode generation is switched off. I think the difference between the releases is that 9.9 is smarter at deciding not to use bytecode generation in cases where it would interfere with tail recursion.

To see why it fails when using function calls rather than templates I would need to see the code. The two cases use different mechanisms internally. In particular functions are by default evaluated in "pull" mode (they return an iterator over the result), templates in "push" mode (they write results out to a result tree). The most noticeable difference is that returning a sequence containing the result of a recursive call (for example select="$x, f:myself($x - 1)) can be done tail-recursively with templates, but not with functions. But that doesn't seem to apply to your case. Also, for templates we handle mutual recursion of two or more templates, while with functions we only handle self-recursion.

The following version appears to work using tail-recursion using either 9.8 or 9.9, with or without bytecode generation. (Under 9.8, though, there is an oddity which I haven't had time to investigate: after producing the output value, the process doesn't actually exit.)