MBQ ответ правильный, но я просто добавлю это:
> `~`(y, x)
y ~ x
> class(`~`(y, x))
[1] "formula"
> terms(`~`(y, x))
y ~ x
attr(,"variables")
list(y, x)
attr(,"factors")
x
y 0
x 1
attr(,"term.labels")
[1] "x"
attr(,"order")
[1] 1
attr(,"intercept")
[1] 1
attr(,"response")
[1] 1
attr(,".Environment")
<environment: R_GlobalEnv>
>