World: r4wp

Hi looking for a better REBOL way to do the next thing: a: [ 1 2 
3 4 5 6 ] I have 1 of the values in this series and  want to do a 
foreach/forall on the series left of this value from right to left 
and also a foreach on the series on the right of this value but now 
from left to right. So say I chose 3 for the value then I need [ 
2 1 ] and [ 4 5 6 7 ]. This is my solution b: reverse copy/part a 
find a 3 and c: reverse copy/part a find reverse a 3 but now >> a
== [6 5 4 3 2 1]

And I don't want that and I don't like undoing the reverse each time. 
Do I need a temp for reverse a because c: reverse copy/part a find/last 
reverse copy a 3
** Script Error: Invalid /part count: 3 2 1
?

You could use FOR to count yourself down:
     blk: [1 2 3 4 5 6]
     val: 3
     for nn val - 1 1 -1 [print blk/:nn]
       2
       1

Thanks Sunanda for this option. One extra tricky thing is the length 
of the series varies and I feel I am doing to much bookkeeping myself 
already.

yes, Arnold, be very careful with reverse... if you are part/way 
it will only reverse part of the series.

a: [ 1 2 3 4 5 6]
b: copy  find/tail a 3 ; you get [4 5 6]
c: reverse copy/part a ((index? find a 3 ) - 1)

and so you get [2 1]

See, there are other ways. Thanks fo the input all!!

And now for something completely different. I have a php based form 
I want to make into a REBOL cgi program. It is to upload some fields 
into an article-base in my mysql database. Where action is article.php 
in the php version I changed this to article.r for the REBOL version. 
I have now the article form shown and when I fill in some fields 
(but not all) and send the form I get the cgi object ( I use safe-cgi-data-read) 
but the contents of the formfields is now empty? Any clues what may 
be the case please?

It is POST data.

I believe that if you do not fill in a field on the form, you do 
not get an item in the cgi objectl.  I seem to recall being confused 
by that for a while.

I might have been wrong on the above comment, or it might apply only 
to checkboxes (that is, if not checked then not present in the object).

web forms do not send data fields when they are empty or "off", this 
is true for all types IIRC.

arnold seems to say that the fields which have data are not sent.

Arnold, actually you can save one copy and the index? computation.
One liner solution:
>> c: reverse copy/part a skip b: find/tail a 3 -2

Oups no need for the skip -2, so it's even a little faster just using 
back
>> c: reverse copy/part a back b: find/tail a 3

Well, I tested again and I was mistaken in thinking php did show 
the field I previously had filled in when returning after submit 
and noticing some field was empty. It is the way the browser refills 
the field when it recognises what you have typed in before.. In the 
php version all fields of the form are empty as well.

So no problem with how REBOL works. (I can display all of the cgi 
block and everything I typed in is there.)

The second thing is the validation I have in mind is in fact a client 
side Javascript/jQuery script before sending the form.

Steeve, I like it. Most of the time I prefer readability over speed. 
This time a little speeding things up comes in handy.

Client-side validation is a nice courtesy touch for the user -- they 
get told of errors without a network delay. But the server-side code 
needs to also do full validation as there is no way of guaranteeing 
the data has been POSTed from your form....Or perhaps the user had 
Javascript turned off.

Sunanda, absolutely. I went way too fast on this. 

Unfortunately there is no way to refill the form fields from the 
cgi data. Now I say so the DOM and a Javascript maybe able to. I 
tried some little things but it seems to mess things up more than 
doing good.

If you want the server-sideCGI to send updated values to the client-side 
JS for that JS to update the web form.....You may need to look at 
AJAX -- a way for JS to do just that.

Look at my Try REBOL site for a simple AJAX example

Arnold, what you want to use is FORSKIP. It's like FOR, but with 
series references instead of numbers. No modifying REVERSE required.

Here's an interactive example that you can adapt to your script:
>> a: [1 2 3 4 5 6 7]
== [1 2 3 4 5 6 7]
>> i: find a 3
== [3 4 5 6 7]
>> b: back i
== [2 3 4 5 6 7]
>> f: next i
== [4 5 6 7]
>> forskip b -1 [print first b]
2
1
>> forskip f 1 [print first f]
4
5
6
7

FORSKIP f 1 [...] could be replaced with FORALL f [...] if you like.

The only trick is that you either need extra temp vars for the loop 
variables, or to modify an existing temp var. As a bonus in R3, FORSKIP 
and FORALL are faster than FOR or FOREACH, since no rebinding of 
the code block is necessary.

Faster than foreach ? I beg to differ good sir, in R2 those are mezzanines 
and so are slow like hell.
I would only use foreach, while and until.
But with R3, yeah you're right.

Nonetheless, FORSKIP has less overhead than FOR, even on R2. Simpler 
mezz code, no BIND/copy overhead.

You can roll your own code in R2 using WHILE and have it be a little 
faster, but not necessarily a lot faster.

IIRC in all the tests I did, the binding overhead is dwarfed by all 
other considerations. 


a single execution of the block is usually longer than the binding 
process (which is slow, but rebol execution is slower still ;-) . 
 


forskip is by far the slowest loop in R2.  it was several orders 
of magnitude slower than foreach.  and much slower than an until 
block ... not worth it..   I'm happy its native in R3.


obviously, the time spent within the block with relativise the time 
spent in the iteration handling.

FOR is slower. You missed comparing FORSKIP to the other mezz loops. 
FOREACH, UNTIL, WHILE, REPEAT and LOOP are native.

That's in R2. In R3, FORSKIP is also native, and faster than FOREACH.

The only mezz loop in R3 is FIND-ALL. It could be ported to R2 as 
well, where it would be slightly slower; actually, I was surprised 
it wasn't there already.

Okay, thanks FOR this analysis. Concluding, where I am using R2 (because 
I 'need' VID) I use the foreach forall. The moment R3 is released 
including VID or replacement I will rewrite this code, promise!

On the form validation issue. I managed to get things working as 
I initially intented. Using a Javascript function to change the text 
of the field: 
var changer = document.getElementById('fieldid');
changer.value = fieldvalue;
Where fieldvalue was filled from the cgi data block cgi/fieldname

It was really fun to get this right with all the needed double-quotes 
and curly braces that alle represent comments in rebol as you know 
and generate this from within the well-known function emit: func 
[code] [ repend html code]
I had to add an id tag to all the form fields.

Arnold,  what do you mean by foreach forall ?

Arnold, Forall is the worst choice, especially inside another loop.
Just look at the code of forall.by yourself.

Use the foreach before all other options? :)

in R2... yep  :-)

If there is an interest in the basic script with a form with the 
field testing and refilling of field in the case some errors were 
found wrt the input. I make a translated anonimised version showing 
the working.

Maxim, Steeve, in R2 exactly. The script I need these things for 
is slowly progressing now. Lots of testing ideas and making decisions 
for preferred solutions. When it is ready, I will post it on rebol.org

Foreach doesn't go in reverse, so you're back to modifying your data. 
If you want to speed up stuff that FORALL does, just look at the 
source. You can inline the FORALL source, drop the error screening 
stuff and simplify the code in the WHILE. You will end up with something 
that can be as fast as the FOREACH, and in some cases faster.

The "in some cases faster" depends on whether you're going in reverse, 
and how much data you have. REVERSE can have a lot of overhead if 
you have a lot of data, so with enough data it would be faster to 
just work in reverse using a WHILE loop, or possibly better yet a 
REPEAT with an index that you subtract.

Time-out! :D

I have enough information to make my script working with reasonable 
speed. After I publish it on rebol.org we can write out a competition 
to have it gain speed ;)

I wrote a run length encoding function, may be useful for someone 
else too:

rle: func ["Run length encode" b /local v r i j] [
	v: 1 r: copy []
	j: next i: b
	unless empty? b [
		until [
			either all [not tail? j equal? first i first j] [
				v: v + 1 j: next j
			] [
				append r reduce [v first i] v: 1 i: ++ j
			]
			tail? i
		]
	]
	r
]

here is the tests:
>> rle "aaabbcx"
== [3 #"a" 2 #"b" 1 #"c" 1 #"x"]
>>
>> rle []
== []
>>
>> rle ""
== []
>>
>> rle [a]
== [1 a]
>>
>> rle [a a a a a]
== [5 a]
>> rle [a a a a a b b]
== [5 a 2 b]

Endo: I think a much faster version could be coded using PARSE.

But don't I need to write two different set of rules for strings 
and blocks?

And I'm not that good using PARSE, my PARSE expriments usually stuck 
with infinite loops :(

I think it should be doable with one set for both datatypes.

Not quite. You can almost do it in R3, but you need the QUOTE operation 
for blocks, and QUOTE doesn't work on strings.