Re: [ooc-compiler] Language limitation or a compiler bug?

[Norayr C. <no...@ar...>]

I've tried your code with Ofront, which is based on OP2.
---
MODULE test;

CONST x = SYSTEM.VAL (SET, 10);

BEGIN

END test.
---

# ./ofront test.Mod
test.Mod  translating test
     pos    58  err 50

err 50 means
Expression should be constant.
I guess OP2 behave exactly the same way.

Sincerely,
Norayr

On 08/03/11 18:34, Alexander Iljin wrote:
> Hello!
>
>>      I found that it's impossible to do "CONST x = SYSTEM.VAL (SET, 10)",
>>     because "10" is 1 byte, and SET is 4 bytes. And if I do "CONST x =
>>     SYSTEM.VAL (SET, LONG(LONG(10)))", then suddenly I get "expression
>>     is not constant error".
>>     Somehow "10" is a constant, and "LONG(LONG(10))" is not.
>>
>>     Is this a compiler bug or an intentional behaviour?
>
>    I was wrong, the problem is not only with LONG(LONG()), but with SYSTEM.VAL as well.
>
>    Here is the only way to convert integer constant value 10 to SET I found:
>
> VAR
>     set: SET;
>     long: LONGINT;
> BEGIN
>     long := 10;
>     attr := SYSTEM.VAL (SET, long);
>
>    If you try to use "10" instead of "long" in the last line, you'll get the size mismatch error
>    ("Size mismatch between type and expression"). Presumably this is because 10 is 1 byte,
>    and SET is 4 bytes. OK, sounds reasonable.
>
>    But shouldn't it be possible to use LONG() for size promotion? The following also compiles
>    without errors (LONGINT replaced with SHORTINT, added two LONG() calls):
>
> VAR
>     set: SET;
>     short: SHORTINT;
> BEGIN
>     short := 10;
>     set := SYSTEM.VAL (SET, LONG(LONG(short)));
>
>    Now there are two things that surprize me:
> 1. LONG(LONG(10)) does not produce a LONGINT constant 10. And neither does "0000000AH";
> 2. SYSTEM.VAL can't be used in a constant definition (more on that later).
>
>    Is it at all possible to create a constant of a given size? We have 1.E0 and 1.D0 to distinguish
>    between REAL and LONGREAL constants, but do we have a mechanism to say, I need "10"
>    in a LONGINT? SYSTEM.VAL (LONGINT, short) fails with the same size mismatch error.
>
>    The SYSTEM.VAL surprize boils down to this:
>
> CONST num = SYSTEM.VAL (SHORTINT, 10);
>
>    This produces the following error: "Expression is not constant". In this example the SYSTEM.VAL
>    call is a no-op. My question is: what is not constant about it?
>    Doesn't SYSTEM.VAL ALWAYS produce constant result no matter what type it casts to?
>
>    I'd like to ask everyone, Michael van Acken in particular, for advice on this situation. I'm willing
>    to dig into the sources if this is something to be fixed.
>
> ---=====---
>   Alexander
>
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