Re: Operation order in expressions

[Vern Hamberg <vhamberg@xxxxxxxxxxxxxxx>]

Hi Martijn

Yes, you have used the correct version - you have parentheses around the 
expression with the IN operator - the original poster did not have the 
parentheses, like this -

IF NOT FV(i).data_type IN %list('NUMERIC' :'CHAR') ;

Here the NOT operator is trying to change data_type but cannot do so, 
because data_type is not a logical (indicator) value. Hence, this is 
where precedence comes in - NOT is done before IN.

I think the comparison with NOT, as I give above, without any bracketing 
parentheses, works in SQL, which suggests that IN and NOT are different 
kinds of elements in SQL than they are in RPG.

Interesting, I think!

Vern

On 8/17/2023 9:07 AM, Martijn van Breden wrote:
> Hi Vern
>
> I ran into this same thing a while ago.
>
> I don't know if it really is a precedence issue. I found that the NOT is reversing the value of an indicator. The indicator value is provided by the (some_value in %list(...)) construct.
>
> So that makes
>
>        IF NOT (FV(i).data_type IN %list('NUMERIC' :'CHAR') );
>
> return true/*on when FV(i).data_type has a value different than 'NUMERIC'  or 'CHAR'
>
> I haven't tried it without the outer brackets, it might work.
>
> In SQL this would be something like
>
>       ... where field not in (value1, value2, etc)
>
> I doubt if you could do this with placing the 'not' in front of 'field'.
>
> They're just two different languages in the end, isn't it?
>
> Kind regards
>
> Martijn van Breden
> lead software architect
>
>
>
>
> ________________________________
> Van: RPG400-L <rpg400-l-bounces@xxxxxxxxxxxxxxxxxx> namens Vern Hamberg via RPG400-L <rpg400-l@xxxxxxxxxxxxxxxxxx>
> Verzonden: donderdag 17 augustus 2023 13:03
> Aan: RPG programming on the IBM i / System i <rpg400-l@xxxxxxxxxxxxxxxxxx>
> CC: Vern Hamberg <vhamberg@xxxxxxxxxxxxxxx>
> Onderwerp: Operation order in expressions
>
> CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you recognize the sender and know the content is safe.
>
>
>
> Y'all
>
> There was just a post about using NOT and IN in a logical test - 2 of us
> responded to add parentheses.
>
> So I did look up operator precedence in the ILE RPG Reference and found
> this list -
>
> The following list indicates the precedence of operations from highest
> to lowest:
> 1. ()
> 2. Built-in functions, user-defined functions
> 3. unary +, unary -, NOT
> 4. **
> 5. *, /
> 6. binary +, binary -
> 7. =, <>, >, >=, <, <=, IN
> 8. AND
> 9. OR
>
> Higher precedence are done before lower. Operations at the same level
> are done left to right, except **, it says.
>
> BTW, an expression like this, putting NOT with IN -
>
>        IF FV(i).data_type NOT IN %list('NUMERIC' :'CHAR');
>
> is not valid in RPG, while it IS valid in SQL, IIRC.
>
> Regards
> Vern
> --
> This is the RPG programming on IBM i (RPG400-L) mailing list
> To post a message email: RPG400-L@xxxxxxxxxxxxxxxxxx
> To subscribe, unsubscribe, or change list options,
> visit: https://lists.midrange.com/mailman/listinfo/rpg400-l
> or email: RPG400-L-request@xxxxxxxxxxxxxxxxxx
> Before posting, please take a moment to review the archives
> at https://archive.midrange.com/rpg400-l.
>
> Please contact support@xxxxxxxxxxxxxxxxxxxx for any subscription related questions.