Compose two lenses to produce a new lens which represents
focussing first with the first lens, then with the second.
view using the resulting composite lens will first
the first, then the second, while an
view via the first lens,
set into the resulting piece with the second, and then replace the
updated structure in the first with
set. Lens composition
is analogous to the
. syntax of object-oriented programming or to
a flipped version of function composition.
l %.% m
the second lens
#>  4lst %>% set(lns, 1) # returns list(b = c(3,2,5))#> $b #>  3 1 5 #>lst # returns list(b = c(3,4,5))#> $b #>  3 4 5 #>