Rethink Capture() design #685
Description
Non-matching Capture() results default values by design.
In some situations such as AtPath(Any, Capture(...)) these default values are not ergonomic.
$ ngs -p '["a", 1] =~ AtPath(Any, Capture(Int))'
<MatchSuccess matches=[null,null,1] pattern=<AtPath path_pattern=<Type Any with 0 constructor(s) and 1 meta entries> value_pattern=<Capture pattern=<Type Int with 8 constructor(s) and 1 meta entries> name=null dflt=null>> named={}>
Thought: introduce filterr() for recursive filter, solving the exact use case above. Then think about which other methods need the r counterpart. eachrr(). How not to confuse with r suffix in other languages which typically means search from right and recursive. Maybe use _rec suffix.
Thought: non-matching alternative/branch should leave no traces in positional or named matches (captures).
Open issue about filterr(), eachr() and all potential data structures walkers - pre or post visit - how to specify?
_rec suffix sounds like reasonable price to pay for recursive walk