Use views in concretization

[phipsgabler]

To concretize, we need the runtime shapes, and to get them, we actually apply the lenses:

AbstractPPL.jl/src/varname.jl

Line 428 in 9b64dd8

x_inner = get(x, I.outer)

It would be good if this were only views. Related: TuringLang/DynamicPPL.jl#341

[torfjelde]

It would be nice if something like Base.maybeview was implemented for lenses

[phipsgabler]

Yea, I thought about this yesterday after writing. Maybe we can implement some utils locally and then ask the Setfield people whether they want them (although they explicitely exclude new stuff for Setfield, IIRC...)

[yebai]

Fixed by #43?

[phipsgabler]

No, it's not fixed, the implementation of get uses normal indexing (see linked issue).