[R] formula argument evaluation

[Keith Jewell]

On 12/04/2016 11:24, Adrian Dușa wrote:
> I have a simple function such as:
>
> foo <- function(x) {
>      call <- lapply(match.call(), deparse)
>      testit <- capture.output(tryCatch(eval(x), error = function(e) e))
>      if (grepl("Error", testit)) {
>          return(call$x)
>      }
> }
>
> and I would like to detect a formula when x is not an object:
>
> # this works
>> foo(A + B)
> [1] "A + B"
>
> # but this doesn't
>> foo(A + B => C)
> Error: unexpected '=' in "foo(A + B ="
>
> Can I prevent it from evaluating the "=" sign?
> The addition sign "+" hasn't been evaluated, and I was hoping the "=" would
> not get evaluated either. The "=>" sign is important for other purposes,
> not related to this example.
>
> Thank you in advance,
> Adrian
>
> --
> Adrian Dusa
> University of Bucharest
> Romanian Social Data Archive
> Soseaua Panduri nr.90
> 050663 Bucharest sector 5
> Romania
>
> 	[[alternative HTML version deleted]]
>
Did you mean
 > foo (A + B >= C)
??