Nicolas Williams
bd7b48c1b9
Now that #1313 is fixed, |= no longer outputs null when the RHS update expression outputs empty. When a user wants to keep the current value of the LHS they would have the RHS update expression output `.`, so having `empty` achieve the same thing would be redundant. The obvious thing to do is to delete the LHS when the RHS update outputs `empty` (i.e., doesn't output any values). It's reasonable to think that existing programs won't be broken by this change, because reduce and |= not handling empty well is clearly a bug. (Though it's possible that some programs were using empty to quickly terminate reduce or |=, it's not likely. They should use label/break instead.) Prior to this change |= would use the _last_ value output by the RHS update expression. With this change |= will use the _first_ value instead. This change _is_ a minor backwards-incompatible change. It may or may not be acceptable; we'll see. It is a useful change in that it makes |= faster when the update expression produces multiple values.