[REBOL] Re: About Attempt
From: al:bri:xtra at: 27-Dec-2002 9:06
Patrick wrote:
> attempt a
>
> However when 'a is not defined an error is rised.
>
> >> attempt a
> ** Script Error: a has no value
> ** Where: do-boot
> ** Near: attempt a
>
> obviously the right syntax is more like
>
> attempt [a]
> or
> attempt [1 / 0]
>
> Do you think it's worth sending this to RT feedback?
The evaluation of 'a happens "outside" of the value (function!) referred to
by 'attempt.
But you have found a problem with 'attempt.
>> attempt 123
** Script Error: try expected block argument of type: block
** Where: attempt
** Near: if not error? set/any 'value
>> source attempt
attempt: func [
{Tries to evaluate and returns result or NONE on error.}
value
][
if not error? set/any 'value try :value [get/any 'value]
]
>> source try
try: native [
{Tries to DO a block and returns its value or an error.}
block [block!]
]
'attempt should have the same function input type as 'try. That's easy to
correct. Just insert the following into your %user.r file (or get my
%Patches.r script):
attempt: func [
{Tries to evaluate and returns result or NONE on error.}
value [block!]
][
if not error? set/any 'value try value [get/any 'value]
]
Note that I've changed the get-word ":value" to a word "value" as the 'get
isn't needed.
Now 'attempt works properly:
>> attempt [1 / 0]
== none
>> attempt [1 / 2]
== 0.5
>> attempt a
** Script Error: a has no value
** Near: attempt a
>> attempt 123
** Script Error: attempt expected value argument of type: block
** Near: attempt 123
I'll fill out the feedback form as well.
Andrew Martin
ICQ: 26227169 http://valley.150m.com/
