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From: markb@sdcrdcf.UUCP (Mark Biggar)
Newsgroups: net.lang.ada
Subject: Re: CONSTRAINT ERROR raised at runtime
Message-ID: <2596@sdcrdcf.UUCP>
Date: Fri, 24-Jan-86 13:37:24 EST
Article-I.D.: sdcrdcf.2596
Posted: Fri Jan 24 13:37:24 1986
Date-Received: Sun, 26-Jan-86 04:04:48 EST
References: <640@decwrl.DEC.COM>
Reply-To: markb@sdcrdcf.UUCP (Mark Biggar)
Organization: System Development Corporation R&D, Santa Monica
List-Id: <comp.lang.ada>

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