They would have for constraint
`if (isInputRange!Range && isInputRange!(ElementType!Range))`
In case you wouldn't see directly what would they be used for,
it's for tree-like structures. Each element in a Range is also an
input range.
I see 3 obvious functions/templates
- the most important, make an input range from a tree-like range,
e.g `auto treeRange(Range, DepthMode mode)(Range range) `
- a second version for bidir ranges, e.g `reverseTreeRange`
- a functional iteration algorithm: auto `deepIterate(alias Fun,
DepthMode mode, Range, A...)(Range range, auto ref A a)`, which
applies Fun to each element with the ability for Fun to act as a
predicates to stop the iteration. Actually I have this one in my
user library (this is also the reason why I post this today).
Unless I'm blind I cannot see anything that handles trees with a
range interface in phobos.
