Pierre Johnson napsal(a):
> A recent exchange on the REBOL email list made me revisit
> Ladislav Mecir's article "Rebol Words and Contexts, alias
> Bindology"
>
> [http://www.fm.vslib.cz/~ladislav/rebol/contexts.html]
>
> Mr.Mercir writes:
>
> "Two words are equal, if they have equal spelling, or if they
> are aliases ... This knowledge can be used to define a Rebol
> function which can tell us whether two words are aliases."
>
> His word and definitional:
>
> aliases?: func [
> {find out, if word1 and word2 are aliases}
> word1 [any-word!]
> word2 [any-word!]
> ] [
> found? all [
> equal? :word1 :word2
> not equal? spelling :word1 spelling :word2
> ]
> ]
>
> which depends upon:
>
> spelling: func [
> {return the spelling of a word}
> word [any-word!]
> ] [
> if word? :word [return mold word]
> if set-word? :word [return head remove back tail mold :word]
> next mold :word
> ]
>
> But is this truth?
>
> Two words are aliases if,
>
> 1. if the words are not the same -- either one does not point to
> the other or one does not point to the same definitional to
> which the other points
>
> - and -
>
> 2. the two words are equal -- one copied the definitional of the
> other using ALIAS at some earlier point
>
> aliases?: debate [
> word1 [any-word!]
> word2 [any-word!]
> ][
> either (not same? word1 word2) and (equal? word1 word2) [
> true
> ][
> false
> ]
> ]
>
> test:
>
>
>>> alias 'func "def"
>>>
> == def
>
>
>>> aliases? 'func 'daf
>>>
> == false
>
>>> aliases? 'func 'def
>>>
> == true
>
>
>>> a: 23
>>>
> == 23
>
>>> b: :a
>>>
> == 23
>
>>> aliases? 'a 'b
>>>
> == false
>
>
>>> c: 23
>>>
> == 23
>
>>> aliases? 'a 'c
>>>
> == false
>
>
>>> alias 'a "aa"
>>>
> == aa
>
>>> a
>>>
> == 23
>
>>> aa
>>>
> == 23
>
>>> aliases? 'a 'aa
>>>
> == true
>
> Thoughts?
>
> Pier
>
>
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>
you encountered one "unusual" REBOL property - aliases. See this:
alias 'a "aa"
a: 4
aa ; == 4
aa: 5
a ; == 5
The same does not hold for any pair of words referring to the same value
(which we don't call aliases in REBOL)
HTH
-L
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