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19-Apr 16:36 UTC
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RAMBO #3652 unset?

 [1/9] from: apwing:zonnet:nl at: 22-Mar-2005 12:06


Hi Gabriele, thanks for your explanation in RAMBO. Still I have a few remarks / questions. #1. it seems very odd to me that unset and unset? are in fact unrelated! Unset causes a variable to have it's value removed. Unset? checks for datatype unset! #2. Is () the only "thing" with datatype unset! ? If not, what other "things" have this value ? Could you give one or more practical examples of the use of unset! and unset? ? Kind regards, Arie

 [2/9] from: lmecir::mbox::vol::cz at: 22-Mar-2005 15:05


Hi Arie,
>Hi Gabriele, > >thanks for your explanation in RAMBO. > >Still I have a few remarks / questions. > >#1. it seems very odd to me that unset and unset? are in fact unrelated! > Unset causes a variable to have it's value removed. > Unset? checks for datatype unset! >
you are right: unset? is related to unset! exactly like integer? relates to integer! etc.
>#2. Is () the only "thing" with datatype unset! ? > If not, what other "things" have this value ? > Could you give one or more practical examples of the use of >unset! and unset? ? >
check the following expressions: do [] print "" prin "" do does [exit] forever [break] get/any 'uninitialized-variable A "practical example" - a function accepting an optional integer argument: f: func [argument [integer! unset!]] [ print ["Argument:" either value? 'argument [argument] ["not supplied"]] ] f 12 f -Ladislav

 [3/9] from: rotenca::telvia::it at: 22-Mar-2005 15:29


Ladislav Mecir wrote:
>check the following expressions: > do []
<<quoted lines omitted: 3>>
> forever [break] > get/any 'uninitialized-variable
other examples: unset? unset 'a unset? set/any 'a unset 'b unset? do does [return] unset? catch[throw] -- Ciao Romano Paolo Tenca

 [4/9] from: apwing:zonnet:nl at: 22-Mar-2005 16:22


Hi Ladislav / Romano, in order to get a grip I played around with your examples, but I don't understand the following: why give the following 2 cases different results? 1 >>unset 'var
>>unset? 'var
== false 2 >>unset? unset 'var == true The only thing I can think of is that unset! is not a datatype of the variable being unset. E.g. after unset 'x x would not have a datatype of unset! (which I thought was true). Instead unset! would just be the returned value of unset itself only. Thanks! Arie P.S. Ladislav the example of function f is very useful! Romano Paolo Tenca wrote: Ladislav Mecir wrote: check the following expressions: do [] print "" prin "" do does [exit] forever [break] get/any 'uninitialized-variable other examples: unset? unset 'a unset? set/any 'a unset 'b unset? do does [return] unset? catch[throw]

 [5/9] from: rotenca::telvia::it at: 22-Mar-2005 19:07


Arie van Wingerden wrote:
>Hi Ladislav / Romano, >in order to get a grip I played around with your examples, but I don't
<<quoted lines omitted: 10>>
>was true). >Instead unset! would just be the returned value of unset itself only.
1a) unset 'var what happens? - the lit-word! <var> is evaluated and become the word <var> - unset receives the word <var> and unsets the value of the word <var> 1b) unset? 'var what happens? - the lit-word! <var> is evaluated and become the word <var> - unset? receives the word <var> and answers: "false: the value <var> is not an unset! value (it is a word!)" - you can test this with: word? 'var ; == true 2) unset? unset 'var what happens? - the lit-word! <var> is evaluated and become the word <var> - unset receives the word <var> and unsets the value of the word <var> - unset returns unset! - unset? receives the values unset! and answers "true: the value <unset!> is an unset! value" - now you can test the value of <var> with one of : value? 'var ; == false which is the opposite of:: unset? get/any 'var ;==false The unset/unset?/value? stuff is a little strange at the beginning, but when you get the whole frame, all becomes clear. -- Ciao Romano Paolo Tenca

 [6/9] from: rotenca::telvia::it at: 22-Mar-2005 19:18


Romano Paolo Tenca wrote:
> which is the opposite of:: > unset? get/any 'var ;==false >
unset? get/any 'var ;==true (typo error) -- Ciao Romano Paolo Tenca

 [7/9] from: apwing::zonnet::nl at: 22-Mar-2005 20:25


Hi Romano, this was *very* helpful for me! And I guess there are others out there being happy with your explanation. Thanks again, Arie Romano Paolo Tenca wrote:

 [8/9] from: lmecir:mbox:vol:cz at: 23-Mar-2005 12:30


Arie van Wingerden napsal(a):
>Hi Ladislav / Romano, >in order to get a grip I played around with your examples, but I don't
<<quoted lines omitted: 12>>
>Thanks! > Arie
a little note: unset? ... is equivalent to: unset! = type? ... while type? 'variable is always equal to word! HTH

 [9/9] from: apwing::zonnet::nl at: 23-Mar-2005 18:07


Thanks Ladislav! I appreciate all the help Arie Ladislav Mecir wrote:
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