From murdoch.duncan at gmail.com  Sat Apr  9 22:37:28 2011
From: murdoch.duncan at gmail.com (Duncan Murdoch)
Date: Sat, 09 Apr 2011 16:37:28 -0400
Subject: [Rd] Wish there were a "strict mode" for R interpreter. What
 about You?
In-Reply-To: <BANLkTim=6ae2huv+GYQLMtgs2P+GD8_WtA@mail.gmail.com>
References: <BANLkTim=6ae2huv+GYQLMtgs2P+GD8_WtA@mail.gmail.com>
Message-ID: <4DA0C388.8080401@gmail.com>

On 11-04-09 3:51 PM, Paul Johnson wrote:
> Years ago, I did lots of Perl programming. Perl will let you be lazy
> and write functions that refer to undefined variables (like R does),
> but there is also a strict mode so the interpreter will block anything
> when a variable is mentioned that has not been defined. I wish there
> were a strict mode for checking R functions.
>
> Here's why. We have a lot of students writing R functions around here
> and they run into trouble because they use the same name for things
> inside and outside of functions. When they call functions that have
> mistaken or undefined references to names that they use elsewhere,
> then variables that are in the environment are accidentally used. Know
> what I mean?
>
> dat<- whatever
>
> someNewFunction<- function(z, w){
>     #do something with z and w and create a new "dat"
>     # but forget to name it "dat"
>      lm (y, x, data=dat)
>     # lm just used wrong data
> }
>
> I wish R had a strict mode to return an error in that case. Users
> don't realize they are getting nonsense because R finds things to fill
> in for their mistakes.
>
> Is this possible?  Does anybody agree it would be good?
>

It would be really bad, unless done carefully.

In your function the free (undefined) variables are dat and lm.  You 
want to be warned about dat, but you don't want to be warned about lm. 
What rule should R use to determine that?

(One possible rule would work in a package with a namespace.  In that 
case, all variables must be found in declared dependencies, the search 
could stop before it got to globalenv().  But it seems unlikely that 
your students are writing packages with namespaces.)

Duncan Murdoch



[Rd] Wish there were a "strict mode" for R interpreter. What about You?
Duncan Murdoch