[REBOL] Re: Hack
From: joel:neely:fedex at: 28-Dec-2001 18:00
[
This is a repost, as the first attempt seems to have disappeared.
If you get duplicates, please accept my apologies.
]
Hi, Sunanda,
[SunandaDH--aol--com] wrote:
> That's clever stuff...
>
I'm not trying to be "clever" to be difficult! ;-)
My concern, which I probably didn't state well, is that I'd rather
see a mechanism that works for the general case of anonymous
functions (even if -- and I agree with you -- the majority of
code uses defined-and-named-once functions) rather than have a
tool that only works in the simple cases.
> ...but I think it misses the point I'd like
> to make. Take these three functions:
>
> FuncA: func [] [2 / 2 FuncB]
> FuncB: func [] [2 / 2 FuncC]
> FuncC: func [] [2 / 2]
>
> Change any of those 2 / 2 to 2 / 0, invoke FuncA and you'll get
> a message like:
>
> ** Math Error: Attempt to divide by zero
> ** Where: FuncC
> ** Near: 2 / 0
>
> With the 'Where giving me the name of the function. The only way
> we know to get that name is (see Romano's original post) to force
> an error.
>
But, see below...
> That is not a first-class API in my opinion <g>...
>
Agreed. Absolutely.
> I agree that if a function isn't named then Rebol can't show a
> name....But it doesn't follow that therefore it can't give me
> any names at all, ever.
>
But it does raise in my mind the question of whether the name is
as meaningful as some other possible information we might get.
Consider the following...
>> f: reduce [
[ func [x] [x / divisor + 1]
[ func [x] [x / divisor + 2]
[ func [x] [x / divisor + 3]
[ ]
== [func [x][x / divisor + 1] func [x][x / divisor + 2] ...
>> foreach ff f [print ff 4]
3
4
5
>> divisor: 0
== 0
>> foreach ff f [print ff 4]
** Math Error: Attempt to divide by zero
** Where: ff
** Near: x / divisor + 1
Knowing that I happened to have accessed the function via the
(temporary!) reference in a word named FF is of little use, if what
I am really trying to do is find (and, presumably, fix) the defective
code.
Also, consider the following...
>> do func [x][x / divisor + 4] 5
** Math Error: Attempt to divide by zero
** Where: func [x][x / divisor + 4]
** Near: x / divisor + 4
>> g: func [n [number!]] [
[ if 0 < do func [x][x / divisor + 4] n [
[ print "positive"
[ ][
[ print "non-positive"
[ ]
[ ]
>> g 5
** Math Error: Attempt to divide by zero
** Where: func [x][x / divisor + 4]
** Near: x / divisor + 4
in which "Where:" doesn't even have a name, because there isn't one
at all.
By way of contrast, let me mention the behavior of the CALLER
function in Perl. It accesses information in the "stack of current
subroutine calls", which includes the source file name and line
number of each pending evaluation. Knowing where a function is
defined seems to me to be at least as useful as what name the caller
may have used to get to it...
Just my $0.02...
-jn-
