From murdoch.duncan at gmail.com  Sat Feb  7 18:58:14 2015
From: murdoch.duncan at gmail.com (Duncan Murdoch)
Date: Sat, 07 Feb 2015 12:58:14 -0500
Subject: [Rd] WISH: eval() to preserve the "visibility" (now value is
 always visible)
In-Reply-To: <CAFDcVCQBgYK3NRWBAHwXV5YAjCMu4gFzBGNw4C8K=oOKBXbmsA@mail.gmail.com>
References: <CAFDcVCQBgYK3NRWBAHwXV5YAjCMu4gFzBGNw4C8K=oOKBXbmsA@mail.gmail.com>
Message-ID: <54D65236.60202@gmail.com>

On 07/02/2015 12:40 PM, Henrik Bengtsson wrote:
> Would it be possible to have the value of eval() preserve the
> "visibility" of the value of the expression?
> 
> 
> "PROBLEM":
> 
> # Invisible
>> x <- 1
> 
> # Visible
>> eval(x <- 2)
> [1] 2
> 
> 
> "TROUBLESHOOTING":
>> withVisible(x <- 1)
> $value
> [1] 1
> $visible
> [1] FALSE
> 
>> withVisible(eval(x <- 2))
> $value
> [1] 2
> $visible
> [1] TRUE
> 
> 
> WORKAROUND:
> eval2 <- function(expr, envir=parent.frame(), ...) {
>   res <- eval(withVisible(expr), envir=envir, ...)
>   value <- res$value
>   if (res$visible) value else invisible(value)
> }
> 
>> x <- 1
>> eval(x <- 2)
> [1] 2
>> eval2(x <- 3)
>> x
> [1] 3

What's wrong with the workaround?

Duncan Murdoch



[Rd] WISH: eval() to preserve the "visibility" (now value is always visible)
Duncan Murdoch