On the use of 'bind

[fvanzeveren]

Hello,
I am trying to solve the following problem.
I have a word whose value is a literal m-counter: to-word "i".
The application does not know the value 'm-counter and needs to loop using the value of 'm-counter as the interating variable.
The code for :m-counter 1 10 1 [print get m-counter] generates an error:
** Script error: i word is not bound to a context ** Where: get for ** Near: get m-counter,
while for :m-counter 1 10 1 [print i] works as expected... but the application cannot assume that 'm-counter will be 'i. It could be any word choosen by the user..
I also tried for :m-counter 1 10 1 [print bind get m-counter 'm-counter] but this produces the same error.
Is what I tries to achieve possible... and how?

Thank you for your help!

François

[Oldes]

The word variable of the for function is local, so it cannot work as you expect... I would need to know, what is your exact use case?

[Oldes]

Maybe you can find useful proposed cfor function.

cfor: func [
    {General loop based on an initial state, test, and per-loop change.}
    init [block! object!] "Words & initial values as object spec (local)"
    test [block!] "Continue if condition is true"
    bump [block!] "Move to the next step in the loop"
    body [block!] "Block to evaluate each time"
    /local ret
][
    if block? init [init: make object! init]
    test: bind/copy test init
    body: bind/copy body init
    bump: bind/copy bump init
    while test [set/any 'ret do body do bump get/any 'ret]
]
ctx: object [i: 1]
cfor ctx [i < 10][i: i * 2][probe i]

I was thinking about making it as a native and include this function in Rebol, because it may be useful. But hard to say, if it is what you need.

[Oldes]

This may help you as well:

;; having some value in the user's context...
>> i: 1
== 1

;; and a value with a word...
>> m-counter: to word! "i"   
== i

;; trying to get a value of this word throws an error, because the word does not have any context (it is just a word)...
>> get :m-counter           

** Script error: i word is not bound to a context
** Where: get
** Near: get :m-counter

;; but you may use bind to give it the context, like the user's context in this case...
>> get bind :m-counter self 
== 1

You may bind the word to any other context...

>> ctx: context [i: 2]  
== make object! [
    i: 2
]

>> get bind :m-counter ctx  
== 2

[fvanzeveren]

Hello Oldes

Thank you for your quick answer. I finally found an alternative way to reach the desired result.
I am "porting" the script Magic! initially developped by Olivier Auverlot about 20 years ago, focusing on extending the parsing engine (of which I am the author in the original work of Olivier) with new tags like <for>, <while> and <until>.

Regards

François