On 25/02/2010 8:50 AM, Ben wrote:
I was disappointed in this behavior because it seems error-prone.
Suppose I declare an environment
> b <- 1
> p <- proto(expr={
a <- 2
+ ...
+ })
> p$a
[1] 2
> p$b
[1] 1
Presumably if I ask for p$a or p$b later, it's because I'm interesting
in the value of "p$a" or "p$b" that I specifically put inside that
environment. Otherwise I would just ask for "a" or "b". If I'm
asking for "p$b" it the above case, that means I forgot to declare b
inside p. In this case there should be an error telling me that, not
a silent substitution of the wrong quantity.
I think you are looking for a different object model than proto offers.
There aren't many languages that offer the prototype object model.
If someone wanted to do the y$ls() thing, they could always
> y <- proto(a=1)
> with(y, ls())
[1] "a"
Another reason is that there are plenty of other programming languages
that have similar structures and this behavior is very odd.
Which languages are you thinking of? The paper about proto only
mentions Self, LispStat, and Javascript. The Wikipedia page
http://en.wikipedia.org/wiki/Prototype-based_programming has a long list
of obscure ones, but the only additional ones I've used are R, Perl and
Tcl, all with add-on packages.
Duncan Murdoch
In
standard languages asking for "b" inside the "p" object gives you an
error, and no one complains. Even in R, we have this behavior:
> z <- 1
> list(a=3)$z
NULL
(Actually I think the above should be an error, but at least it isn't
1.) So anyway, I'm not saying that p$b being 1 is an outright 2+2=5
bug, but it does seem to be surprising behavior that leads to bugs.
But I'm sure you're right that there are historical/structural reasons
for this to be the case, so perhaps there's no solution.
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