cumsum on a RleList fails when the last element is empty.

[charles-plessy]

cumsum tolerates empty elements in a RleList unless the empty element is in terminal position…

> RleList(Rle(), Rle(1), Rle(1)) |> cumsum()
RleList of length 3
[[1]]
numeric-Rle of length 0 with 0 runs
  Lengths: 
  Values : 

[[2]]
numeric-Rle of length 1 with 1 run
  Lengths: 1
  Values : 1

[[3]]
numeric-Rle of length 1 with 1 run
  Lengths: 1
  Values : 1

> RleList(Rle(1), Rle(), Rle(1)) |> cumsum()
RleList of length 3
[[1]]
numeric-Rle of length 1 with 1 run
  Lengths: 1
  Values : 1

[[2]]
numeric-Rle of length 0 with 0 runs
  Lengths: 
  Values : 

[[3]]
numeric-Rle of length 1 with 1 run
  Lengths: 1
  Values : 1

> RleList(Rle(1), Rle(1), Rle()) |> cumsum()
Error: subscript contains out-of-bounds indices

I solve the problem as follows in my package but it is a bit ugly.

> safe_cumsum
function(x) {
  x <- c(x, Rle(1))
  cs <- cumsum(x)
  head(cs, -1)
}
<bytecode: 0x563e22a916f0>
> RleList(Rle(1), Rle(1), Rle()) |> safe_cumsum()
RleList of length 3
[[1]]
numeric-Rle of length 1 with 1 run
  Lengths: 1
  Values : 1

[[2]]
numeric-Rle of length 1 with 1 run
  Lengths: 1
  Values : 1

[[3]]
numeric-Rle of length 0 with 0 runs
  Lengths: 
  Values : 

It would be nice if cumsum would tolerate lists ending with an empty element.