Re: language problem

[ms8k#@andrew.cmu.edu.UUCP]

In article <8703261730.AA28726@taurus> amiram@TAURUS.BITNET.UUCP writes:
>A colleague of mine, Yossi Veler of AITECH has come up with the following
>program in Ada, which seems to create a serious problem.
>
>procedure boolsub is
>   subtype bool is boolean range true..true;
>   type arr is array(1..10) of bool;
>   a : arr := (1..10 => true); -- this seems like the only legal value
>begin
>   a := not a;
>-- Here a(1)=a(2)=...=a(10)= FALSE !!!! No exception occurs etc.
>   a := (1..10 => false);
>-- This does cause an exception
>end boolsub;
>
>The program seems legal : we inspected the LRM and also the implementers
>guide, and we ran it on both the DDC and VERDIX compilers. It seems that
>a combination of innocent features in Ada produces a result that seems to
>contradict with the basic philosophy of the language, that is an object
>posseses a value which is not in the appropriate type.

Verdix Ada v1.5 is completely bogus. Don't be amazed by problems like this.
Another example is

    type BYTE is range 0 .. 255;
    for BYTE'SIZE use 8;

Verdix compiler says that the size is too small.

    type BYTE is new POSITIVE range 0 .. 255;
    for BYTE'SIZE use 8;

same thing! 0 as a POSITIVE does not disturb it. The bit sign is still there.

    type BYTE is range -128 .. 127
    for BYTE'SIZE use 8;

is ok (at last), but is not really what was wanted. Another solution may be
an enumaration of 256 items, a little painful. 

____________________________________________________________
Marc A. Scheurer

Arpanet, Bitnet: ms8k@andrew.cmu.edu
UUCP           : seismo!andrew.cmu.edu!ms8k
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