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From: tmoran@acm.org
Newsgroups: comp.lang.ada
Subject: Re: Why is Ada NOT a good choice for a beginner to programming?
References: <3E06EF4A.A72F3B82@t-online.de>
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Xref: archiver1.google.com comp.lang.ada:32251
Date: 2002-12-23T19:54:21+00:00
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> Sure, but there are some sort of statements where the compiler KNOWS
> that there an exception will be raised. So - why not give a warning at
> compile time? The Aonix compiler do so!!!
  Do you think other compilers don't?

procedure testerr is
  a : positive;
begin
  a := 0;
end testerr;

Gnat
testerr.adb:4:08: warning: value not in range of type "Standard.positive"
testerr.adb:4:08: warning: "constraint_error" will be raised at run time

Aonix
testerr.adb: Warning: line 4 col 8 LRM:11.5(17), Value outside range, Constraint_Error will be raised
*****Warning: At line 4 in ..\testerr.adb.  Constraint_Error will be raised here if executed [value outside range].

Janus
In File E:\claw133\finder\TESTERR.ADB at line 4
--------------
    3:  begin
    4:    a := 0;
---------------^
*WARNING* Expression is always out of range (6.5.1)

(The Janus manual 6.5.1 says "An expression has an unchanging value that
is not within the appropriate range bounds.  This will always raise
Constraint Error."  The Janus error messages have a short sentence,
a reference to a short paragraph in the Janus manual, and usually, though
not in this case, an ARM reference.)

OTOH, none of the three detected at compile time that an exception
would be raised by

procedure testerr is
  a : positive := 2;
begin
  for i in 1 .. 2 loop
    a := a-1;
  end loop;
end testerr;