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[REBOL] Re: Puzzle with FIND and SELECT

From: lmecir:mbox:vol:cz at: 10-Feb-2003 17:23

Hi Joel, ...
> - Why do we need SAME? at all? One use is to distinguish mutable > values so that one can determine in advance whether a change via > one "access path" will affect what is visible via another?
SAME? is not useful for this purpose. The reason is as follows: you can find two values that clearly aren't the same, like e.g. a: [1 2] b: next a A and B are Relatives in the above sense and a mutation of A can affect B even though A and B are neither same nor equal. For the cases like above the RELATIVES? equivalence (in ) is better suited.
> That > said, are there others?
See the applications of the IDENTICAL? function (in ).
> Does this imply that immutable values > of the same type (see below) which are equal are indistinguishable?
This is a proven thing for me (in ).
> - Do we need more state into the semantic model? Even if we accept > the notion that "every REBOL value is in a block...", some blocks > are inaccessible (e.g. blocks resulting from the load/eval/print > cycle at the console). This already means that we can't take any > arbitrary expression and wrap it in a function without the risk > of changing its semantics, as in the classic REBOL-newbie koan: > > >> repeat i 10 [append [] i] > == [1 2 3 4 5 6 7 8 9 10] > >> foo: func [n [integer!]] [repeat i n [append [] i]] > >> foo 5 > == [1 2 3 4 5] > >> foo 5 > == [1 2 3 4 5 1 2 3 4 5]
Moreover, even if we could wrap any expression in a function/block/whatever, how can we guarantee, that any value will be in a one and only one block and not more, and that it will be at exactly one position of the block?
> And my proposed solution is that a DECIMAL! value and an INTEGER! > value should never be SAME? (even if EQUAL!) because they *are* > distinguishable by some means in the language (TYPE? of each). > > Since RT apparently has chosen TYPE? to be a discriminator for > FIND and SELECT it should be relevant to SAME? at least AFAIAC.
... Agreed. Regards -L