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From: mike@peregrine.UUCP
Newsgroups: net.lang.c
Subject: boolean datatype
Message-ID: <393@peregrine.UUCP>
Date: Sat, 31-May-86 21:41:11 EDT
Article-I.D.: peregrin.393
Posted: Sat May 31 21:41:11 1986
Date-Received: Tue, 3-Jun-86 23:57:35 EDT
References: <5498@alice.uUCp> <1462@mmintl.UUCP> <852@bentley.UUCP> <1126@whuxl.UUCP>
Reply-To: mike@peregrine.UUCP (Mike Wexler)
Organization: Peregrine Systems, Irvine, Ca
Lines: 52
Summary: why to booleans would be nice

This is not a proposal to change the ANSI standard.  This is just some
ideas some possible ways of improving C.
>Re: builtin bool type
>>I'm not sure why not.  Assuming all the implicit int/bool conversions stay,
>>I think the only problems are (a) it isn't really necessary, and (b) it adds
>>a new reserved word (breaking any programs that use "typedef int bool"!).
>
>(a) is the biggie.  Why add bool when "typedef enum { FALSE, TRUE } bool;"
>works fine?  (Relying on ANSI C's treatment of enums as real ints)
So that the built in statements can use them.
	...
	int n,get_number();

	n=7;
	if (n=get_number()) printf("got 7\n");	/* should have been ==		*/
	...
This is an example of a place where a C compiler with boolean types would catch
a mistake.
	...
	bool flag,get_yes_or_no();

	if (flag=get_yes_or_no()) printf("got yes\n");	/* no mistake		*/
	...
This is an exmaple of a place where most of the idea for finding mistaken
assignments would fail.

One possible way to put this in C would be to do the conversion from
int to bool(if the integer is not equal to zero then make it true else
make it false) and generate a warning.  This would add a new reserved
word and would break programs that used bool as an identifier.  At
some future time the warning could become an error message.

Another feature I would like to have is a range data type.  I don't
know of a good syntax for putting this in C but it would be nice to
use in programs where are know the possible values of a number but
would like the compiler to figure out an efficient sized slot to put
it in.
	...
	range hour:1..12; /* create a variable named hour that can vary from */
				/* 1 through 12								*/
	typedef range DAY:1..366;
	DAY day1,day2;

	hour+=2;
	day1=day2+100;
}
I will let other people argue about how to index an array by a range. 
-- 
Mike Wexler
Email address:(trwrb|scgvaxd)!felix!peregrine!mike
Tel Co. address: (714)855-3923
;-) Internet address: ucivax@ucbvax.BERKELY.EDU!ucivax%felix!mike@peregrine :-(