World: r3wp

Yes, on a particular field I want to control what the user can and 
can't enter

On one field I want to trap and convert any chars to uppercase, but 
also stopthe user from antering more than say 5 chars !

either 5 > length? face/text [
	; allow event to pass through
][
	exit ; too many chars ! don't allow it !
]

or combining filter with length check:
if any [
	not find "0123...89" event/key
	5 <= length? face/text
][
	exit
]

Yeah I was trying to approach it with ( if chars < 6 allow it ) which 
got me in a mess.

I'm sorry for all these questions - It sounds like I want you to 
do my work for me! I don't maind having to figure some things out 
myself . But I was asked to present waht I found difficult from a 
newbie point of view.

you're lucky to have us around, otherwise some of this would take 
a long time to figure out. I was frustrated for a long time about 
many of these things.

Very True, hopefully I will be able give back - in time

particularly bindings can be baffling, because it looks like function 
names are pulled out of thin air. :-)

Yes, I'm starting to understnad dialects and domains. Bindings I'm 
clue-less (LOL)

Yes on Antons one liner with the three filed and overriding the tab 
to filed three the 'bind' is alien to me!

field !

bindings are actually simply tieing a word to a list of words (a 
context), which is an object. outside the context, the word has no 
meaning, yet it can appear anywhere in code

I believe this is how local words work in a function definition. 
the words don't work outside the function, because they are bound 
to its context.

Right one of the fundamentals of Rebol is that Word behaviour can 
change or is set by what contaxt it's in ?

yes, by using the BIND function, you can bind a word to one or more 
contexts simultaneously.

yet it can appear anywhere in code

 <--- actually that's a bit wrong. if the word is not defined for 
 a particular context, then of course it's useless there. but if you 
 use the word in the right context, for example inside an object in 
 which it was originally created, then it will have meaning.

you can study this by creating objects with words in them and try 
to bind them to different contexts (other objects).

I understand that. Are contexts just what I would call an object?

Ah! you just answered that  ;-)

yes. try:

make object! []

and context []

and see what's returned

or more revealing:

>> source context

context: func [

    "Defines a unique (underived) object." 

    blk [block!] "Object variables and values."

][

    make object! blk

]

it's all just a big re-dress of objects. :-)

Think I get it - It's the object oriented side of Rebol - you could 
say that bind is a sort of inheritance ?

more like membership. there is no real inheritance in Rebol.

Yes, MS always partly implemented OO in VS. they didn't think there 
users could handle them !  Java is more of a full OO implementation 
but I find you end up having to override most objects and that's 
not good for code re-use.

OO is ok but it doesn't always fit the real world (or programming 
productivity). that's why I think OO Databases have never really 
been adopted! they fit models but not the real world (Where the customer 
say's Ahh! didn't we mention that !! (LOL).

This should be instructive. Type this into the console a line at 
a time:

o1: context [my-word: "hello"]
o2: context [my-word: "there"]
o3: make object! [my-word: "SteveT"]

code: []
append code in o1 'my-word
append code in o2 'my-word
append code bind [my-word] o3

print code

I first show two different ways of creating an object, and then I 
show two different ways of getting a word in an object.

I got a halt-view near my-word?

Show me the code and resulting error.

Maybe you missed one of the single-quotes before a 'my-word (which 
makes it a lit-word!)

eg.  in o1 'my-word   ; <-- don't miss the '

o1: context [mu-word: "hello"]
>> o2: context [my-word: "there"]
>> o3: make object! [my-word: "SteveT"]
>> code: []
== []
>> append code in o1 'my-word
== [none]
>> append code in o2 'my-word
== [none my-word]
>> append code bind [my-word] o3
== [none my-word my-word]
>> print code
none there SteveT

Yep think so that 's what i got now

first line says "mu-word" :)

Dohhh! it's this eclectic keyboard lol

'my-word is therefore not in o1 and so:    in o1 'my-word  == none

:)

first o1
first o2

Lists the words in each object, if you don't believe what IN is telling 
you.

Or of course you can use HELP or ?.

? o1
? o2

Think I understand that

Each word carries its binding with it. ie. a reference to an object. 
(or no object if it is unbound).

Can you get problems if an  object gets bound to itself?

An object is a container of word -> value pairs. When you ask for 
a word's value, the word's binding is checked to get the object.