Support nested progressbars

[DanChaltiel]

Hi,

It would be very nice if progress bars could be nested.

For instance, consider this code:

library(purrr)
pb_out = list(format="Outer: {pb_current}/{pb_total} {pb_bar} {pb_percent}")
pb_in = list(format="\tInner: {pb_current}/{pb_total} {pb_bar} {pb_percent}")

walk(1:10, ~{
  walk(1:5, ~{
    Sys.sleep(1)
  }, .progress=pb_in)
}, .progress=pb_out)

As for purrr 1.0.1, each progress bar appears on the same line and overwrites the other one.

If the inner could be on the next row and leave the outer be, it would be a great feature!

[hadley]

Unfortunately this isn't possible due to limited support for consoles to change lines in this way.