## digitalmars.D - a<b<c?

- xs0 <xs0 xs0.com> Feb 12 2005
- zwang <nehzgnaw gmail.com> Feb 12 2005
- xs0 <xs0 xs0.com> Feb 13 2005
- "Miguel Ferreira Simões" <Kobold netcabo.pt> Feb 12 2005

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

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

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

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