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[REBOL] Re: A REBOL challenge - The Information World

From: larry:ecotope at: 7-Dec-2001 12:19

Hi Gregg,
> Regarding use of 'protect: Can you protect an entire context, or the words > *in* a context? I haven't figured out how to do that yet. >
PROTECT basically adds a protected flag to a word value. A REBOL value of datatype word includes a pointer to its context. The use of PROTECT will protect the word in that context. The argument to PROTECT can be either a word or a block of words. For contexts created by the function USE, which creates a local context for execution of a block of code, the use of PROTECT is straightforward:
>> use [a] [a: 1 protect 'a loc-a: does ['a]]
We have created a local context with the word 'a' being the only local variable. In the code block we create a global function LOC-A which returns the local word 'a', so that we can see what's happening. The word 'a' is both private and (after the PROTECT 'a) protected.
>> a: 52
== 52 The global word 'a' is set to 52.
>> loc-a
== a
>> get loc-a
== 1 We can access the value of the local 'a'. But it is protected from change.
>> set loc-a 2
** Script Error: Word a is protected, cannot modify ** Near: set loc-a 2 But because we have the word, we can use the UNPROTECT function on it.
>> unprotect loc-a >> set loc-a 2
== 2
>> get loc-a
== 2 For local contexts created by MAKE FUNCTION! and MAKE OBJECT! the situation is more complex and the usefulness of PROTECT is limited. BTW In future, with REBOL/Core 3.0, we have been told that REBOL will have modules, which should alleviate most of the currently existing namespace issues. -Larry