Re: Operation order in expressions

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

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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
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