[REBOL] Re: [subject: error and trial]
From: lmecir:mbox:vol:cz at: 5-Mar-2002 8:46
Hi Pat,
your code is almost correct, it just omits one special case. See the
following example:
>> type? a: make error! "my error"
== error!
>> u-def? 'a
== true
>> undefined? 'a
== false
Cheers
L
------------------
From: "pat665"
Sent: Monday, March 04, 2002 10:54 PM
Subject: [REBOL] [subject: error and trial]
Hi rebollers,
I am coming again with a question posted on November the 23th 2001. At the
time, I thought I had understood Ladislav's answer, but the truth is I am
not so sure.
All began while reading Ladislav's contexts.html...
There are Words that do not have the ability to refer to Rebol values. We
can call them undefined Words. [ ...] This function can be used to find out,
if a Word is undefined:
undefined?: func [
{determines, if a word is undefined}
word [any-word!]
] [
error? try [error? get/any :word]
]
My question was "why use error? two times?". In my eyes, a more simple
version of the function could be :
u-def?: func [
{determines, if a word is undefined}
word [any-word!]
] [
error? try [get/any :word]
]
We can test these two functions whith Ladislav's own example of an undefined
word.
a-word: first first rebol/words ;== end!
>> undefined? a-word
== true
>> u-def? a-word
== true
>> undefined? 'print
== false
>> u-def? 'print
== false
I am not pretending I am right, because I must be wrong! but I deeply need
to understand where and why !
Patrick
