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digitalmars.D - a<b<c?

reply xs0 <xs0 xs0.com> writes:
Hi!

I always wondered why no language includes such syntax (of those I know, 
at least), but wouldn't it be possible to have this?

if (a < b <= c < d) ...

It looks much more obvious (and prettier and shorter) than

if ((a < b) && (b <= c) && (c < d)) ...

And this is also a common mathematical notation, afaik..

It is perfectly OK, if it is evaluated just the same as the long form 
(with short-circuiting and everything).

I'm not sure whether to allow this:

if (a < b > c)

But I guess there is no harm, again it gets translated to (a<b) && (b>c)..



xs0
Feb 12 2005
next sibling parent reply zwang <nehzgnaw gmail.com> writes:
xs0 wrote:
 Hi!
 
 I always wondered why no language includes such syntax (of those I know, 
 at least), but wouldn't it be possible to have this?
 
 if (a < b <= c < d) ...

This is a perfectly legal expression in D and many other languages, though semantically equivalent to (((a<b)<=c)<d) rather than ((a<b)&&(b<=c)&&(c<d)).
 
 It looks much more obvious (and prettier and shorter) than
 
 if ((a < b) && (b <= c) && (c < d)) ...
 
 And this is also a common mathematical notation, afaik..
 
 It is perfectly OK, if it is evaluated just the same as the long form 
 (with short-circuiting and everything).
 
 I'm not sure whether to allow this:
 
 if (a < b > c)
 
 But I guess there is no harm, again it gets translated to (a<b) && (b>c)..
 
 
 
 xs0

Feb 12 2005
parent xs0 <xs0 xs0.com> writes:
 if (a < b <= c < d) ...

This is a perfectly legal expression in D and many other languages, though semantically equivalent to (((a<b)<=c)<d) rather than ((a<b)&&(b<=c)&&(c<d)).

Well, I know that, but wouldn't it be much more natural if it was the second form? I can't think of a case where I'd want it compiled as (((a<b)<=c)<d), while the other case happens very frequently.. I think if this is something the parser can easily handle, it'd be a nice feature to have.. xs0
Feb 13 2005
prev sibling parent "Miguel Ferreira Simões" <Kobold netcabo.pt> writes:
Recently, in college, I have done an intermediate compiler, that compiled a 
language similar
to Matlab to triple address code (3ac).

When I was doing the grammar that question came up too!

As you said, mathematicians use the notation: a < b < c, which means that b 
belongs to the open interval ]a , c [ and is equivalent to (a < b) && (b < 
c).

However, imho, I think there is some ambiguity, because programming 
languages implement boolean expressions and it can have another meaning:
     (a < b) < c.
Which evaluates to: ((a < b) ? 1 : 0) < c

Miguel Ferreira Simoes
Feb 12 2005