Meaning of error using . shorthand inside dplyr function - r

Question

I'm getting a dplyr::bind_rows error. It's a very trivial problem, because I can easily get around it, but I'd like to understand the meaning of the error message.
I have the following data of some population groups for New England states, and I'd like to bind on a copy of these same values with the name changed to "New England," so that I can group by name and add them up, giving me values for the individual states, plus an overall value for the region.
df <- structure(list(name = c("CT", "MA", "ME", "NH", "RI", "VT"),
estimate = c(501074, 1057316, 47369, 76630, 141206, 27464)),
class = c("tbl_df", "tbl", "data.frame"), row.names = c(NA, -6L))
I'm doing this as part of a much larger flow of piped steps, so I can't just do bind_rows(df, df %>% mutate(name = "New England")). dplyr gives the convenient . shorthand for a data frame being piped from one function to the next, but I can't use that to bind the data frame to itself in a way I'd like.
What does work and gets me the output I want:
library(tidyverse)
df %>%
# arbitrary piped operation
mutate(name = str_to_lower(name)) %>%
bind_rows(mutate(., name = "New England")) %>%
group_by(name) %>%
summarise(estimate = sum(estimate))
#> # A tibble: 7 x 2
#> name estimate
#> <chr> <dbl>
#> 1 ct 501074
#> 2 ma 1057316
#> 3 me 47369
#> 4 New England 1851059
#> 5 nh 76630
#> 6 ri 141206
#> 7 vt 27464
But when I try to do the same thing with the . shorthand, I get this error:
df %>%
mutate(name = str_to_lower(name)) %>%
bind_rows(. %>% mutate(name = "New England"))
#> Error in bind_rows_(x, .id): Argument 2 must be a data frame or a named atomic vector, not a fseq/function
Like I said, doing it the first way is fine, but I'd like to understand the error because I write a lot of multi-step piped code.

Answer 1

As #aosmith noted in the comments it's due to the way magrittr parses the dot in this case :
from ?'%>%':
Using the dot-place holder as lhs
When the dot is used as lhs, the
result will be a functional sequence, i.e. a function which applies
the entire chain of right-hand sides in turn to its input.
To avoid triggering this, any modification of the expression on the lhs will do:
df %>%
mutate(name = str_to_lower(name)) %>%
bind_rows((.) %>% mutate(name = "New England"))
df %>%
mutate(name = str_to_lower(name)) %>%
bind_rows({.} %>% mutate(name = "New England"))
df %>%
mutate(name = str_to_lower(name)) %>%
bind_rows(identity(.) %>% mutate(name = "New England"))
Here's a suggestion that avoid the problem altogether:
df %>%
# arbitrary piped operation
mutate(name = str_to_lower(name)) %>%
replicate(2,.,simplify = FALSE) %>%
map_at(2,mutate_at,"name",~"New England") %>%
bind_rows
# # A tibble: 12 x 2
# name estimate
# <chr> <dbl>
# 1 ct 501074
# 2 ma 1057316
# 3 me 47369
# 4 nh 76630
# 5 ri 141206
# 6 vt 27464
# 7 New England 501074
# 8 New England 1057316
# 9 New England 47369
# 10 New England 76630
# 11 New England 141206
# 12 New England 27464