[R] Why does 'exists' need a quoted argument?

[Morten Sickel]

Kevin Wright wrote:
/snip/
>Can someone explain why 'get' and 'exists' require quoted object names?

>Would it make sense (more consistency) to have these functions check to see
if the 
>first argument is a string, and if not, then 'substitute' it?
Intuitively, >'exists' is checking to see if an object exists, not to see if
a character string 
>exists.  Evidently my intuition is wrong.

Well, if you read the ?exists you'll see that it "Search for an R object of
the given name on the search path". Even though I am absolutely no R
developer, I would guess that it would be not impossible to write a function
that does as you thinks, but, its functionality would be worse than for the
current exists, consider for example:

<code>
sql<-Big_ugly_slow_query
sql2<-some_more_parameters
for (i in c("Foo","Bar","Baz"))
  if (!exists(i)){ 
	assign(i,sqlquery(handle,paste(sql1,i,sql2)
  }
}
</code>

i.e. if the object doesn't exist, I have to initialize it, if it does exist,
I just keep on using it, I know that the object i exists, so I don't care
about that. On the other hand, if it was automatically substituting what was
found to be a string, it would not be possible to

<code>
if (!exists("String")){String<-"Default value"}
</code>

So, no, I think some useful functionality would be thrown out if exist did
not require a string.

Morten Sickel