Re: CONSTRAINT ERROR raised at runtime

[markb@sdcrdcf.UUCP (Mark Biggar)]

In article <640@decwrl.DEC.COM> cook@katie.DEC (Neil on 225-7155) writes:
>>    LNTH : NATURAL range 1..8 := 0;
>
>In the index of ANSI/MIL-STD-1815A-1983 (The Programming Language
>Ada Reference Manual), under the entry CONSTRAINT_ERROR, is a reference
>to "raised by the initialization of an object 3.2.1".
>
>In that section, paragraph 16, it says "The initialization of an object
>... checks that the initial value belongs to the subtype of the
>object ... The exception CONSTRAINT_ERROR is raised if this check fails."
>
>I take "The initialization..." to be a reference to the run-time
>behaviour. Since the run-time environment raises CONSTRAINT_ERROR, I think
>the compiler behaves correctly.

A very close reading of the LRM shows that there is no reason why the
compiler shouldn't complain, it just doesn't have to.  Section 1.6 para 5
says:

"If an exception is certain to be raised in every execution of a program,
 then compilers are allowed (although not required) to report this fact
 at compilation time."

So the compiler DOES behave correctly, it just could have behaved in a more
user friendly way then it did.

Mark Biggar
{allegra,burdvax,cbosgd,hplabs,ihnp4,akgua,sdcsvax}!sdcrdcf!markb