[R-SIG-Mac] A shorthand for '<-'

[Herve Pages]

Hi,

John Chambers wrote:
[...]
> In a sense "=" inside a function call is not semantically an operator at 
> all; it's absorbed by the parser into the internal structure that 
> represents the call.  In contrast, putting an assignment operator inside 
> an argument to a function is very different (and, IMO, something to be 
> avoided in writing clear S-language code.)

Not only in S or R. I would say this should be avoided in any language
where the order in which the function args are evaluated is undetermined,
especially in situations like this one:

  b <- 0
  f(a <- b + 1, b <- 7) # will call f(1, 7) or f(8, 7)?

[...]
> Again, the parser prohibition comes from catching a classic programming 
> error in C (and another complaint about using "=" as an assignment 
> operator).
> 
> while(flag = 0) { // of course, I meant (flag == 0)
>   ...
>   if(something(...)) flag = 1;
> }
> 
> after which the programmer wonders why the loop never exits.

You mean, the loop will never enter.

Cheers,
H.