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World: r3wp

[Core] Discuss core issues

ChristianE
23-Mar-2010
[16049x3]
Jim, bad news first: By design functions in REBOL have no name. In 
REBOL, Functions are first class values which /may/ be referenced 
by one word, by more than one word or by no word at all
E.g.:
>> calc: reduce [func [v] [v / 2] func [v] [v * 2] func [v] [v * 
3]]
== [func [v][v / 2] func [v][v * 2] func [v][v * 3]]

>> do reduce [first calc second calc third calc 1]
== 3

>> set [half double triple] calc
== [func [v][v / 2] func [v][v * 2] func [v][v * 3]]

>> half double triple 1
== 3

>> set [a b c] first calc
jdishun
23-Mar-2010
[16052]
Thanks Christian Is there any good news?
ChristianE
23-Mar-2010
[16053x11]
The functions in the CALC block have no names at all. But you can 
assign them to words, as is done later on. You can assign one function 
to different words. What's the name of the first function in CALC, 
is it 1) HALF, is it 2) A, is it 3) B or is it 4) C ? There is virtually 
no way for REBOL to decide that.
Good news there are.
There are implementation details which may be used (as in: may be 
"hacked") to get the desired effect. Just give me a moment to dig 
for the answer to your question
>> test: func [/local self] [self: get in disarm self: try [1 / 0] 
'where print ["My name is" uppercase form self]]
>> test
My name is TEST
Oops
>> test: func [/local self] [self: get in disarm try [1 / 0] 'where 
print ["My name is" uppercase form self]]
>> test
My name is TEST
But be carefull
>> again: :test
>> again
My name is AGAIN
The exact same function may return another name if assigned to another 
word.
Or it may return no name at all:
>> do reduce [:test]
My name is NONE
Steeve
23-Mar-2010
[16064]
nice trick
ChristianE
23-Mar-2010
[16065x2]
Credit where credit belongs, that trick is courtesy of Gabriele.
Who was the first to come up with this trick iirc.
jdishun
23-Mar-2010
[16067]
I probably didn't explain it well -- that's the behavior I want! 
Including the NONE.


Clever - I understand about creating an error object.  ... I could 
look look it up, but can you give me a quick explanation of  "/local" 
- sounds very interesting.
ChristianE
23-Mar-2010
[16068x9]
All words after the /LOCAL refinement are words local to the function, 
all words preceeding /LOCAL are function arguments
>> additon: func [one two /local three] [three: one + two] 
>> addition 1 2
== 3
The above can be written as
>> test: function [] [self] [self: get in disarm try [1 / 0] 'where 
print ["My name is" uppercase form self]]
>> test
My name is TEST
(a function with no arguments and one local word SELF)
Way shorter:
>> test: does [print ["My name is" uppercase form get in disarm try 
[1 / 0] 'where]]
>> test
My name is TEST
(no local words here)
With DOES being shorthand for a function with no arguments.
jdishun
23-Mar-2010
[16077]
I'm out of synch - but  --does  "self" have special meaning or is 
it just a varible name? If so how does it get set to  the name.
ChristianE
23-Mar-2010
[16078x3]
No, SELF is as good a word as any other, the above example with DOES 
shows that you don't need a word at all.
Just break it into little steps:
>> test: function [] [error me] [error: disarm try [1 / 0] probe 
error me: error/where print ["My name is" uppercase form me]]
>> test
make object! [
    code: 400
    type: 'math
    id: 'zero-divide
    arg1: none
    arg2: none
    arg3: none
    near: [1 / 0]
    where: 'test
]
My name is TEST
jdishun
23-Mar-2010
[16081]
Now I think I remember -- the error object contains the name of the 
function -- correct?
ChristianE
23-Mar-2010
[16082x2]
So to say. It isn't very precise, though. What's happening here is:
In the disarmed error object REBOL tells you where your code breaks; 
it breaks when trying to evaluate the word 'TEST
jdishun
23-Mar-2010
[16084]
Yes - the "little steps" reminds me about "where". That nails it

Many many thanks.
ChristianE
23-Mar-2010
[16085]
In a strict sense, REBOL doesn't tells you the name of the function 
(it can't), it rather tells you where in your code the error occurs. 
The error occurs when you try to evaluate the TEST word.
Graham
23-Mar-2010
[16086]
Not sure where to put this ... so  ...


I am running a number of server processes ... not necessarily listening 
on any ports, though some are.

What's the best way of tracking them all to make sure that they are 
all working?

I guess the processes that aren't listening on a port could touch 
a file
jdishun
23-Mar-2010
[16087]
Christian - Appreciate the clarification Works for me!
ChristianE
23-Mar-2010
[16088]
You're welcome!
Steeve
23-Mar-2010
[16089]
Great work, would be a nice alias to add in Rebol.

>> whereof: [get in disarm try [+] 'where]

>> g: f: does [print ["my name is" do whereof]]
>> g
my name is g
>> f
my name is f
ChristianE
23-Mar-2010
[16090]
>>	I guess the processes that aren't listening on a port could touch 
a file


Likely the easiest way to go, I've always went for that approach, 
Graham. Renaming files afaik is an atomic operation, so you can toggle 
process states between %process-a.running  and %process-a.finished 
or %process-b.failed etc. Not suggesting that there aren't better 
ways ...
Steeve
23-Mar-2010
[16091]
obviously, it can't be a mezz
ChristianE
23-Mar-2010
[16092]
Steeve, please make sure that BrianH doesn't see what you are suggesting 
here ;-) That method is so wrong!
Steeve
23-Mar-2010
[16093x2]
eh why that ? :)
it's rebolish enough for me
ChristianE
23-Mar-2010
[16095x2]
Mainly, I was just kidding.
On the other hand, it really is just a dirty hack, not more. The 
main point is, it doesn't provide an answer to the function's "What 
is my name?"-question. Functions have no names.
Steeve
23-Mar-2010
[16097]
(If you want BrianH accept it, just let him think he find the trick 
himself)
ChristianE
23-Mar-2010
[16098]
I'm not argueing that it wouldn't come in handy sometimes ... If 
you know what you do.