[REBOL] Re: Multi-searches
From: brett:codeconscious at: 21-Feb-2002 20:44
Hi Philippe,
> Could you explain me this line :
> while [all [not tail? series found? series: find/only series value]][
Andrew's formatting maybe have explained it for you, but if not, some more
detail is below.
> I use ALL like that "all [(first test)(second test)] [consequence]" but
here
> ? and what does the rest of the line ?
First off, in case it helps, a quick correction to your example. ALL takes
only one parameter, a block. The "[consequence]" part of your example
is not used by ALL at all. Probably your example is part of an IF
statement like this:
IF condition [consequence]
E.g:
>> if true [now]
== 21-Feb-2002/20:00:37+11:00
>> if all [1 2] [3]
== 3
Now on to ALL.
ALL evalutes a block of expressions. If during that evaluation one of
those expressions results in none! then ALL returns none!. If all the
expressions are not none! then ALL returns the result of the last
expression. Examples:
>> all [1 2 3 4 5]
== 5
>> all [1 2 now]
== 21-Feb-2002/19:50:44+11:00
>> all [1 2 none 4 5]
== none
Back to my line. I intended this part of the line:
[
not tail? series
found? series: find/only series value
]
to have two results.
The first result is to make sure that there is something left to process.
The second result is true only if the value is found in the the remaining
part of the series.
If either of these results in none! ALL will return none! and the while
loop will stop. When both are true it means that I have a value to
process.
The second result may look odd to you. I didn't really need to use
found?
but I did to emphasize where the second result was going
to come from. You can as easily delete "found?" from the line - the
condition will still work.
find/only series value
finds the value in the series. If the value is
found then the result of this is the same series but it's index
(position) modified to where the value occurred. I capture this
result into the same variable "series". If the value was not found
you get a none!
So the series index gets moved up if a value is found. It gets
moved to the value.
The body part of the while loop runs for each value that is
found. It adds the value to the result and then it moves
the series index again to prevent an infinite loop.
I hope that is helpful!
Regards,
Brett.
