Why does '->'(12, b) give an error?

Question

In R operators can also be expressed as a function call, e.g.

'<-'(b, 12)

for b <- 12.
Why does the following give an error:

'->'(12, b)

? (The code 12 -> b works as expected.)

Answer 1

Because operators are "translated" to functions by the parser and both left and right assignment are parsed to the <- function. There is no right assignment function.

e <- quote(b <- 12)
as.list(e)
#[[1]]
#`<-`
#
#[[2]]
#b
#
#[[3]]
#[1] 12

e <- quote(12 -> b)
as.list(e)
#[[1]]
#`<-`
#
#[[2]]
#b
#
#[[3]]
#[1] 12