Assertions (was: Re: next "big" language?? (disagree))

[bobduff@world.std.com (Robert A Duff)]

In article <4ql1fv$5ss@goanna.cs.rmit.EDU.AU>,
Dale Stanbrough  <dale@goanna.cs.rmit.EDU.AU> wrote:
>...Can anyone think of a better
>name (pragma Declare(x) is not available in Ada) than "Fact"?

pragma Assume?

Actually, I don't see a need for these two separate pragmas.  We can
have:

    pragma Assert(...);

and:

    pragma Suppress(Assertion_Check);
    pragma Assert(...);

for these two cases.  Note that in *both* of these cases, the compiler
can optimize the following code based on the asserted "fact".  These
pragmas are really no different from constraint checks, which may or may
not be suppressed, and which can, of course, affect the behavior of the
program.

The third case that Robert mentioned -- an assertion that cannot affect
the behavior of the program in any way -- is quite impossible to define
in language terms.  It very well might be a useful thing, though.

- Bob