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[REBOL] Re: Words with no value error

From: tim:johnsons-web at: 8-Jan-2004 8:54

* M&F <[the--optimizer--tiscali--it]> [040108 08:26]:
> > Hi all, > I have menaged to read all the over 400 messages from this list sent > during last month... :P > > I have a question about the " Script Error: xxx has no value" problem. > > I have seen that there's no way to trap such an error, which is not a > syntax one. > > 'value? does not work, nor does 'error?.
Hi Mauro: Try this little console session to get a feel for rebol words and values. Then read my comments at the end.
>> t: attempt[x]
== none
>> y: 2
== 2
>> t: attempt[y]
== 2
>> value? 'x
== false
>> print 'x
>> print x
** Script Error: x has no value ** Near: print x Think of a rebol word as a white-space delimited string. a rebol word may or may not have a value. But it always has a spelling. If you've done anything with LISP or scheme, this is the inspiration for rebol.... Testing for a value requires a single quote as in value? 'x as opposed to value? x Using 'attempt is guaranteed to return a 'none if the word has not value. There is a tutorial on rebol evaluation techniques using my 'fetch function (somewhere) you might want to dig into that some time. HTH tim -- Tim Johnson <[tim--johnsons-web--com]><