[Rd] grDevices::grey could provide clearer error message when length(alpha) != length(level)

[Duncan Murdoch]

On 10/05/2018 9:17 AM, Hugh Parsonage wrote:
> e.g.
> 
> grDevices::grey(level = 0.1, alpha = c(0, 1))
> #> Error in grey(level = 0.1, alpha = c(0, 1)) :
> #>  attempt to set index 1/1 in SET_STRING_ELT
> 
> Perhaps
> #> Error in grey(level = 0.1, alpha = c(0, 1)) :
> #>  lengths of 'level' and 'alpha' differ
> 

Or it could return a vector of length 2.  This is not how it is 
documented to operate, but it is how many other R functions handle 
vectors of mixed lengths.

Duncan Murdoch