[R] R design (was "Variable passed to function not used in function in select)

[Terry Therneau]

 I've read the back and forth this morning, and I have to side with Vince.
 
 1. Functions that re-interpret their arguments are very dangerous.  The 
original question involved a well formed call to a function, which returned the 
wrong answer.  Bug, design flaw, whatever -- it's a mistake and the best choice 
would be to fix it.
  I only consider such behavior in 2 cases:
  	a. when the function is almost never, ever, called from anything but the 
top level.  help() is the only example I can think of.
  	b. to create a label from an argument, as in plot, but the argument 
itself is left alone to work as it should.
  	
One possible fix for subset: first treat the argument formally, and only if that 
simple interpretation fails try the more 'clever' interpretations.  Whether this 
is doable or not I can't say.  	
 
  2. The documentation of subset is not in any way clear.  I would never have 
been able to diagnose or work around this bug.  The issues are very subtle.  
  I quite often see "it's in the manual so we bear no blame" as an argument on 
this list.  We all need to remember that our view of what we are particularly 
close to is a distorted one -- I for instance think that everything about the 
survival package is crystal clear --- and be particularly open to concerns that 
something is opaque or subtle.
  
  3. I've heavily used perhaps 20 computing languages in my life.  I found S to 
be a refreshing revalation (referring to S of the 1988 Blue manual) precisely 
because it was completely functional.  Once I got used to it, this feature made 
it so much more useful, extensible, understandable than other things I'd used.
   
   R is becoming less and less a functional language (hidden functions and 
dependencies with environments for one), I quite often cannot figure out either 
exactly what a function calls or how to get it to stop doing it.  I am not sure 
we have gained with each choice of "convenience" or sophistication over 
functional purity.  I want "scan(file=myfile)" to continue to return "variable 
myfile not found" when I forget the quotes.
     
   I am stumped by the R results I get too often, and I'm not a novice.  That 
said, good design is hard.  I spend a lot of time on that aspect in the survival 
package and there are still bits where the 'right' way is only clear after 
several years experience.  I do occassionaly make non-backwards compatable 
changes.  The R core team has done an amazing job on the whole.
    
   And let's not shoot the bearers of bad news.
   
   	Terry T