Duncan Murdoch wrote:
> On 11/8/2007 11:51 AM, Thomas Lumley wrote:
>
>> On Wed, 7 Nov 2007, Duncan Murdoch wrote:
>>
>>
>>> At first I thought you were complaining about the syntax, which I find
>>> ugly. There was a proposal last year to overload + to do concatenation
>>> of strings, so you'd type cat("x=" + x + "y=" + y + "\n"), but there was
>>> substantial resistance, on the grounds that + should be commutative.
>>>
>>>
>> My objection, at least, was that + should be *associative*. I don't think
>> anyone would expect a + b and b+a to be the same for strings, but I do
>> think the fact that (a+b)+c and a+(b+c) would be different (if some of a,
>> b,c were strings) has real potential for ugliness.
>>
>
> Sorry, I forgot about that. I think there were complaints about both
> commutativity and associativity.
>
> I do think lack of associativity is a less impressive complaint, because
> it doesn't even hold for floating point addition without mixing types:
>
> > x <- .Machine$double.eps/2
> > A <- (1 + x) + x
> > B <- 1 + (x + x)
> > A == B
> [1] FALSE
>
> As far as I can see, string concatenation would only lose associativity
> when some of the operands were automatically converted to strings.
> Mixed type operations often give surprising results.
>
>
Exactly. But the issue in that case is not a difference on the order of
Machine$double.eps but between "24" and "222" (from "2"+2+2).
Still, even numbers act up once you get into recycling rules: Try
1:2+1:3+1:4
(We've been here before, haven't we?)
> Duncan Murdoch
>
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