[REBOL] Re: Puzzle with FIND and SELECT
From: lmecir:mbox:vol:cz at: 10-Feb-2003 16:22
Hi Joel,
----- Original Message -----
From: "Joel Neely"
> Romano Paolo Tenca wrote:
> >
> > But i know that every rebol value is in a block at a given position.
> > Beyond its attributes, it has a block position.
> > Literal values, for example, have never the same block position:
> >
> > same? "a" "a"
> > same? 1 1
> >
> > should result both false.
> >
>
> Which raises the following questions IMHO:
>
> - Why? If "same" means "indistinguishable by any means (within
> the language)" then aren't all occurrences of e.g. 1 the "same"?
>
> - 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? That
> said, are there others? Does this imply that immutable values
> of the same type (see below) which are equal are indistinguishable?
>
> - 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]
>
> - Are we cracking an egg with a sledgehammer? I started this thread
> with a puzzle that cost me more time than I care to admit when it
> came up in debugging a small script. In a nutshell, the issue was
>
> >> foo: [1 2 3.0 4 5] == [1 2 3 4 5]
> >> find foo 3 == none
> >> equal? foo/3 3 == true
> >> same? foo/3 3 == true
>
> 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.
>
> >
> > So i think that same? gives the correct result only for mutable
> > values.
> >
>
> All of these (my) comments are dangerous, being about what REBOL
> "should" do in the opinion of (at least one of) its users, and not
> about what REBOL was intended to do in the opinion of its creator.
>
> It would be nice to hear from Carl about the original intent
> behind some of these things.
>
> -jn-
I suggest you to send this to the feedback.
Regards
-L
