In R-4.1.2 and R-devel from two weeks ago I do not get the `<-<-`:
str.language(parse(text = "a <- b = c"))
expression: structure(expression(a <- b = c), sr ...
language: a <- b = c
symbol: =
language: a <- b
symbol: <-
symbol: a
symbol: b
symbol: c
identical(parse(text = "a <- b = c")[[1]], parse(text = "`=`( `<-`(a, b),
c)")[[1]])
[1] TRUE
str.language() is a rudimentary parse tree displayer:
str.language <- function(expr, name = "", indent = 0)
{
trim... <- function(string, width.cutoff) {
if (nchar(string) > width.cutoff) {
string <- sprintf("%.*s ...", width.cutoff-4, string)
}
string
}
cat(sep="", rep(" ", indent), typeof(expr), ": ",
if(length(name)==1 && nzchar(name)) { paste0(name, " = ") },
trim...(deparse1(expr, width.cutoff=40), width.cutoff=40),
"\n")
if (is.function(expr)) {
str.language(formals(expr), name="[formals]", indent = indent + 1)
str.language(body(expr), name="[body]", indent = indent + 1)
} else if (is.recursive(expr)) {
expr <- as.list(expr)
nms <- names(expr)
for (i in seq_along(expr)) {
str.language(expr[[i]], name=nms[[i]], indent = indent + 1)
}
}
invisible(expr)
}
-Bill
On Fri, Feb 4, 2022 at 9:34 AM Duncan Murdoch <murdoch.duncan at gmail.com>
wrote:
Here's an odd parse:
a <- b = 1
This appears to be parsed as
`<-<-`(a, b, 1)
instead of being equivalent to
a <- b <- 1
I wonder if that's intentional?
(This showed up at https://stackoverflow.com/q/70989067/2554330, where
it caused a lot of confusion. I think the original intent was that `a`
would be a macro holding `b = 1`, but I'm not sure of that.)
Duncan Murdoch