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

[rav@goanna.cs.rmit.EDU.AU (++ robin)]

	ok@goanna.cs.rmit.edu.au (Richard A. O'Keefe) writes:

	>euahjn@eua.ericsson.se (Henrik Johansson) writes:

	>>*But* Ada lacks the general
	>>assertion expression found in other languages like Eiffel (preconditions,
	>>postconditions, assertions).

	>	subtype Assertion is Boolean range True .. True;
	>	...
	>	X_Is_Even: Assertion := X mod 2 = 0;

	>This will raise a constraint exception if the assertion is false.
	>Looks like an assertion to me.

---What is the point of this?

   A declaration buried somewhere else, and a test.

   Why not something in clear english, which doesn't need a
reference to some other part of the program, like:

   if mod(x, 2) ^= 0 then
	put ('The value of x is not odd.');

This has the aditional benefit that the user of the program
has a clear unequivocal message about the cause of the problem.
If it's important that the whereabouts of this test be known,
the programmer can include a statement such as "signal error;"
or "signal condition (xyz);" or "put (' at line ', sourceline );"
along with the put statement. [PL/I example]