World: r3wp

You can also have a look at dispatch

I was wondering if I am going about searching for particular values 
wrong. If I have a block of objects  and I want to search for a particular 
value within one of those objects should I go though each obj using 
something like "foreach" or is there a better way.
For example
movies: [m1 m2 m2]
where m1 is an object with a "title" value, etc.

foreach movie movies [
  if movie/title == "Star Wars" [.....]
]
Of course that works but it seems primitive.

I'd be interested in seeing what others do in this situation as well. 
 I believe most people would be using one of the sql options available 
to clean this up.

I know there is a sql dialect out there, it would be interesting 
to know how it performs this type of query.

Don't confuse "primitive" with "simple and obvious".  :-)  Without 
trying to avoid answering your question (what you're doing is fine 
:-), let me ask some questions in return:


What is your goal? Do you want to improve readability? Allow users 
to enter queries? Improve performance? What goes in the [....] block? 
What would you have to do to perform this task *without* examining 
each object?

Gregg, well in the back of my mind since I started programming with 
BASIC, C and Assembler (which, without wanting to start an Altme-war, 
I refer to as 'procedural' as opposed to OO), I was just wondering 
if there was another "object-oriented" way. You know, like "find" 
but with special parameters that tell it to do what my "foreach" 
actually does. I don't know, it just seemed kind of "Dorky." : )

I'm writing an app that will produce php code to help me administer 
mysql db's. I'm at the point where it can read the table and field 
data and create objects with that info. Now I'm at the part where 
it goes back and pulls that data out. So, I've assigned each table 
an index # then in the "columns" object, it refers back to that index. 
Since I have a block of those column objects I was just looking for 
a spiffy way of finding which ones, for example, of finding all of 
the objects that are part of table index #3.

I've always used the "foreach " method but you know, I'm always looking 
for a way to improve my code. Thanks Gregg for your input.

James, are you after a search three? Do you know those data structures? 
Examples are binary search threes, B-threes, etc.

Do you mean tree?

Yes, of course! Tree! Sorry about that.

Actually I was just wanting to know if I was missing something in 
the way I am checking for a value within an object that is part of 
a block of objects. Nothing really sophisticated and these blocks 
are really small so no need for speed increases. 

To be frank,  I often look at the code you all write and say to myself: 
" Self, how in the world did they think of that?" or "Oh, I didn't 
know you could do that." For example when I first started using Rebol, 
I didn't know about the  "in" word as in "Get in object 'word.." 
so I was always using paths and trying to figure out how one would 
make the path a "variable." (object/mypath, where mypath could be 
some changing value). 
Thanks for your input though.

Maybe you could make a block with the titles and the objects together, 
and then just use a path to get to the object? Something like:


>> movies: reduce ["Star Wars" make object! [status: 'good!] "Matrix" 
make object! [status: 'cool]]
>> movies/("Star Wars")/status
== good!
>> movies/("Matrix")/status
== cool

I'm just throwing ideas! :-) Work with it.

You see, stuff like that is very interesting to me.

I didn't know you could use ( ) like that.

I think, we were allowed to use () in paths in recent versions of 
REBOL. Not exactly sure when.

Why doesn't anyone tell me these things? : )

james_nak: http://www.rebol.com/article/0025.html:)

it's almost three years...time runs so fast :)))

Another thing to consider is that this is a general need, so FOREACH 
(e.g.) may be used, but you can hide it in a wrapper func, maybe 
called SELECT-ALL, that works like REMOVE-EACH. I have different 
variations, based on how other langs do it, e.g. select/inject in 
smalltalk. Here's a very quick way to leverage REVMOE-EACH.

    filter: keep-each: func [

        "Keeps only values from a series where body block returns TRUE."

        'word  [get-word! word! block!] "Word or block of words to set each 
        time (will be local)"
        series [series!] "Series to traverse"

        body   [block!]  "Block to evaluate. Return TRUE to collect."
    ] [
        remove-each :word series join [not] to paren! body
    ]
    comment {
        filter x [1 2 3] [x = 2]
        filter x [1 2 3] [odd? x]
        filter res [1 2 3] [odd? res]
        filter [x y] [a 1 b 2 c 3] [all [odd? y  'c = x]]
    }

Thanks Gregg and Rebolek!

pekr,sqlab, thank you for your answers. I thought that sync ports 
also had a timeout like the async kernel (set-modes port [timeout: 
30]) but they do not. thanks

I may be the last to learn this, but I didn't know you could do this:

>> type? first [none]
== word!
>> type? first [#[none]]
== none!

which is neat :-)

Any thoughts on this?

>> #"a" * 2
== #"Â"
>> 2 * #"a"
== 194


So multiply is commutative in a 'funny' way. In this example, you 
get the result in the same datatype as the first argument. This also 
works:

>> #"a" * 2.0
== #"Â"

But you can't do:

>> 2.0 * #"a"
** Script Error: Cannot use multiply on decimal! value


So multiply is not commutative, when it comes to decimals and chars. 
Any comments? Also think of other datatypes, you wanna multiply.

I think I would avoid using that feature  often

I once heard that R2 doesn't allow you to free memory and that R3 
will.  Anyone know if we are able to free memory in R2?  I think 
it was concerning a stats command discussion somewhere.

Paul; Check http://www.rebol.org/cgi-bin/cgiwrap/rebol/view-script.r?script=free-mem.r
for a small blurb and a way to free memory in R2.

Newer versions of REBOL allow a simple  unset 'var  recycle  sequence. 
 But GC is voodoo a lot of times, not just in REBOL, so there are 
probably cases that this won't apply.

Hi Rebol community, I was wondering about how you deal with error 
handling in Rebol in those situations where you have a number of 
network operations which are likely to fail part of the time. Of 
course, you already raised the timeout for network protocols (system/schemes/default/timeout: 
0:10). Now say your script contains a number of network operations 
(read url, for example) wrapped in user functions. This is a very 
common situation.

For example:

fetch-actual-ip: does [

        page: read-url-with-basic-auth http://192.168.1.1/Status.htm(http-basic-auth-key 
        router_username router_password)
	parse page [thru <td class="stdbold" nowrap> copy ip to </td>]
	return to-tuple ip
]


Now this is fine, but if your read operation fails, the script will 
abort. You would like the function to try again a couple of times.


The first thing you would be tempted to do is to redefine the function 
to repeat the function in case of error or unexpected result. A recursive 
function like the next one may provide some solace: 

fetch-actual-ip: does [

        page: read-url-with-basic-auth http://192.168.1.1/Status.htm(http-basic-auth-key 
        router_username router_password)
        either none? tmp: find/tail page "ip address"
                [
                print "Retrying..."
                retries: retries + 1

                if retries > 10 [print "Retried 10 times. Exiting" quit]
                fetch-actual-ip
               ] [

                parse tmp [thru <td class="stdbold" nowrap> copy ip to </td>]
                retries: 0
                return to-tuple ip
                ]
]


You might have a number of user functions and each can fail, so transforming 
every user function into a recursive one with its own error handling 
block can be tedious. 


Wouldn't it be better to abstract the process with a meta-function 
that accepts as input the user function itself? The error handling 
logic would then be exclusively handled by that meta-function, which 
will save you from redundancy if you have multiple user functions. 

Let's do it:


retry: func [external_function [function!] retries [integer!] /local 
.retry [function!] tries [integer!] value] [
	tries: 0
	.retry: func [.external_function [function!]] [
		either not error? try [value: .external_function]
			[
			if not none? value [return value]
			]
			[
			print "Retrying..."
			tries: tries + 1

   if tries > retries [print rejoin ["Tried function " tries " times. 
   Exiting"] return]
			.retry :.external_function
			]
	]
	.retry :external_function
]

Now you call the short version of fetch-actual-ip like this:

retry :fetch-actual-ip 5

(try the user function 'fetch-actual-ip up to 5 times)

Anyone wants to comment or improve on this?

One difficulty is to refine the meta-function 'retry to accept user 
functions with a variable number of arguments. Tricky. Anyone got 
an idea?

provide the argument list in a block to the retry function

It can seem like more work, but and FSM based model works well IMO.

From section 11.12 of the Core users manual:

inp: open/binary/direct ftp://ftp.site.com/big-file.bmp
out: open/binary/new/direct %big-file.bmp
buf-size: 200000
buffer: make binary! buf-size + 2

while [not zero? size: read-io inp buffer buf-size][

    write-io out buffer size  ;<================<<< Where did size come 
    from; this is incorrect, no? 
    total: total + size
    print ["transferred:" total]
]

Whoops!  Watch out for wordwrap.

Sorry. I see it now. My mistake.

Exactly, Graham, argument passing in a block is a decent solution. 
I saw here and there rebol code implementing this for similar purposes. 
I'll repost a an updated 'retry version when I get around it.

Attention whoever is in charge of documentation. Section 11.12 of 
the Core Users Manual give an example that will not work. A clear 
buffer statement is needed after the write-io line, and the ports 
need to be closed after sending each file.

Gregg, do you mean Finite State Machine. Care to expand?

Ok, here is an updated version of 'retry. What is it?  It is a higher 
-level function that takes as input a user function and repeats it 
the number of times specified. The current version handles user functions 
that take arguments.

Usage:

retry :user_function 5 

For a user function that doesn't take arguments

retry/args :user_function 5 [args]

For a user function that take arguments


retry: func [user_function [function!] retries [integer!] /local 
.retry [function!] tries [integer!] value [any-type!] args_length 
[integer!] /args block [block!]] [
	tries: 0
	args_length: length? first :user_function

 if ((args_length > 0) and (not args)) [print ["User function require" 
 args_length "arguments. Provide them in a block and use the /args 
 refinement."] return]
	if not args [args_length: 0 block: []]
	.retry: func [.user_function [function!]] [

  either not error? try [value: do compose [.user_function (copy/part 
  block args_length)]]
			[
			if not unset? value [return value]
			]
			[
			print "Retrying..."
			tries: tries + 1

   if tries > retries [print rejoin ["Tried function " tries " times. 
   Exiting"] return]
			.retry :.user_function
			]
	]
	.retry :user_function
]

Everybody is invited to improve on this.

I wrote 'retry to use in scripts heavy in network calls where failure 
is, by nature of the internet, common, so instead of aborting when 
such a failure occurs, I can use 'retry to repeat individual functions 
any number of times I wish, improving the success of the script.

>> retry: func [code times] [
[    loop times [
[        attempt [
[            break/return do code
[            ]
[        ]
[    ]

>> retry [1 / probe -1 + random 2] 5
0
1
== 1

Very elegant, and concise, Gabriele. Maybe you can propise have an 
expanded version to handle arguments the code should be invoked with

Sorry, I pressed Enter by mistake, here I go again: Very elegant, 
and concise, Gabriele. Maybe you can propose an expanded version 
that can handle arguments that the code should be invoked with.

That's what 'retry currently does.

If you provide that capabilty, I take your version in no time. Mine 
is too obscure.

Another requirement is tthat if the code returns a value, retry should 
return that exact same value as well. I believe your version currently 
doesn't.

After reading about /no-set to reduce, is this an error? / inconsistency?

>> reduce ['s: 3 * 3]
== [s 9]

shouldn't it be

== [s: 9]

?