Hello folks,  I have been writing a flex compatible lexer for D and have come up against the following points in the docs.

S.      hexadecimal floats are in the spec only prefixed with 0x Q.      should 0X be allowed as well?

S.      imaginary numbers are only identified with i or I
Q.      should j or J be allow too (as this is commonly used
        in the engineering world)

S.      <>
Q.      What is this expression? Is it a not equal?

S.      >>> and >>
Q.      this is shift arithmetric right and shift right?

(source for the lexer is in the D.gnu news group)

C 2002/6/11

"C.R.Chafer" <blackmarlin@nospam.asean-mail.com> wrote in message news:ae5bo3$2u97$2@digitaldaemon.com...

> Hello folks,  I have been writing a flex compatible lexer for D and have come up against the following points in the docs.
>
> S.      hexadecimal floats are in the spec only prefixed with 0x Q.      should 0X be allowed as well?

Well, it is in DMD.

> S.      imaginary numbers are only identified with i or I
> Q.      should j or J be allow too (as this is commonly used
>         in the engineering world)

Never heard of it before, really. The "i" suffix is a traditional math approach.

> S.      <>
> Q.      What is this expression? Is it a not equal?

Floating-point inequality (RTFM the section on operators).

Pavel Minayev wrote:

> > S.      imaginary numbers are only identified with i or I
> > Q.      should j or J be allow too (as this is commonly used
> >         in the engineering world)
>
> Never heard of it before, really. The "i" suffix is a traditional math approach.

I ran into this when studying electrical engineering.  The phase & amplitude
of sinusoidal AC signals are modeled with complex numbers.  Since i usually
was a variable name for current, they didn't want to use i as the imaginary
number.  Thus, the use of j:
    v = 1 + 3j;
    i = 2 + 4j;

It's not a key feature, but it's probably a good one.

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"Russ Lewis" <spamhole-2001-07-16@deming-os.org> wrote in message news:3D064128.BD5286BB@deming-os.org...

> > Never heard of it before, really. The "i" suffix is a traditional math approach.

   Yes, "i" and "j" are both used. Math, physics and engineering types do
have different ways of expressing the same things. Like the difference
between F'(x) and dF(x)/dx to express derivatives.

> Thus, the use of j:
>     v = 1 + 3j;
>     i = 2 + 4j;
>
> It's not a key feature, but it's probably a good one.

   I only see one problem, though: another cool feature of the language
would be to natively support quaternions (4D complex numbers that are widely
used in 3D animation), which use "i", "j" and "k" as the three imaginary
parts:

v = 1 + 3i + 4j - 2k;

   <ahem> <cough> Still, I believe it would be best if such mathematical
concepts could be implemented by libraries instead of having to be native to
the language itself. </cough> </ahem>

Salutaciones,
                         JCAB

Pavel Minayev wrote:

> "C.R.Chafer" <blackmarlin@nospam.asean-mail.com> wrote in message news:ae5bo3$2u97$2@digitaldaemon.com...
> 
>> Hello folks,  I have been writing a flex compatible lexer for D and have come up against the following points in the docs.
>>
>> S.      hexadecimal floats are in the spec only prefixed with 0x Q.      should 0X be allowed as well?
> 
> Well, it is in DMD.

Though so - must be a bug in the docs.

>> S.      imaginary numbers are only identified with i or I
>> Q.      should j or J be allow too (as this is commonly used
>>         in the engineering world)
> 
> Never heard of it before, really. The "i" suffix is a traditional math approach.

And the "j" suffix the traditional engineering approach (due to "i" being commanly used to represent a current variable).

>> S.      <>
>> Q.      What is this expression? Is it a not equal?
> 
> Floating-point inequality (RTFM the section on operators).

Yes,  my fault - found it ment unordered compare about 5 minutes after I posted this.

C 2002/6/11