[REBOL] Re: RAMBO #3652 unset?
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
