Mark H Weaver <m...@netris.org> writes: > l...@gnu.org (Ludovic Courtès) writes: >> I’m not completely convinced it makes sense to “specify” the zero values >> case in this way, but I’d like to hear what others think. > > I'm strongly opposed to having core Guile mechanisms automatically > convert between SCM_UNSPECIFIED and zero values, which is part of what > David's patch set does. I'd be glad to explain the reasons for my > position in a later message, but I don't have time right now. > > However, I'm (cautiously) open to the idea of changing (if #f x) and > some other things to return (values) instead of *unspecified*. I agree > that it would be cleaner, though I worry about backward compatibility > issues.
The C API recommends using SCM_UNSPECIFIED here. That was never different. Consolidating this will not really work without declaring SCM_UNSPECIFIED and consequently *unspecified* the same as (values). This strategy is also sketched in a comment by Andy where *unspecified* is defined. What this patch does for backward compatibility reasons is treating *unspecified* as an immediate value in single-value contexts. This will likely always be the case in the C API where all calls of "values" are sort of half-transparent anyway. It is conceivable to eventually deprecate this use in Scheme proper. This won't be doable without a migration strategy. The conversions this patch uses in the Scheme/VM layer are such a migration strategy. Step 1 would be this patch. Step 2 would be putting out deprecation warnings. Step 3 would be removing the automatic conversions. Compatibility considerations will make the last two steps a large hurdle. I don't see a better step 1 towards the goal of letting (if #f x) return (values). I readily agree that this is a mess. Where we disagree is in the culprit. You consider this patch the cause of the mess, I consider this patch consolidation of the SCM_UNSPECIFIED/*unspecified* mess already designed into GUILE. > It would have to be done between major releases. In the current form of the patch, it's surprisingly backwards compatible but of course one would not call it a mere bug fix. It will take a number of major releases to get more than step 1 done. But every journey starts with the first step. -- David Kastrup
