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From: franka@mmintl.UUCP (Frank Adams)
Newsgroups: net.lang.c
Subject: Re: Additions to C - range checking
Message-ID: <1616@mmintl.UUCP>
Date: Mon, 30-Jun-86 19:42:49 EDT
Article-I.D.: mmintl.1616
Posted: Mon Jun 30 19:42:49 1986
Date-Received: Thu, 3-Jul-86 00:43:01 EDT
References: <523@ccird1.UUCP>
Reply-To: franka@mmintl.UUCP (Frank Adams)
Distribution: net
Organization: Multimate International, E. Hartford, CT
Lines: 24

In article <523@ccird1.UUCP> rb@ccird1.UUCP (Rex Ballard) writes:
>if (5<a<50) do_something(a);
>
>this would currently be interpreted as
>
>if((5<a)<50).  since, if a=100 (5<a) evaluates to 1 and 1<50, it
>is true for any number greater than 5 right?

Well, yes; but if a is not greater than 5, then (5<a) is zero, which is also
less than 50; so this is in fact always true.

>Is this impossible to parse?

A little tricky, but not impossible.  To my knowledge (I don't know
everything), only COBOL actually does this.  I, for one, think it's a good
idea; but for new languages, please -- don't try and change C to accomodate
it.  Once you have assigned a meaning to a<b<c, it is impractical to try and
change it.  (There is one easy-to-implement rule which does permit this to
be added in an upward compatible way -- make a<b<c illegal.  Ada does this;
in some other languages it is semantically illegal, since comparison operators
are not permitted to operate on boolean expressions.)

Frank Adams                           ihnp4!philabs!pwa-b!mmintl!franka
Multimate International    52 Oakland Ave North    E. Hartford, CT 06108