dsimcha wrote:
== Quote from Robert Jacques (sandf...@jhu.edu)'s article
On Sat, 07 Nov 2009 10:48:11 -0500, KennyTM~ <kenn...@gmail.com> wrote:
On Nov 7, 09 18:43, Don wrote:
Walter Bright wrote:
Don wrote:
A little while ago I said I'd create a patch for ^^ as an
exponentiation. A couple of people had requested that I make a post
to the ng so they'd know when it happens. Here it is.
This is opPow(), x ^^ y
http://d.puremagic.com/issues/show_bug.cgi?id=3481
I don't understand the rationale for an exponentiation operator. It
isn't optimization, because pow() could become an intrinsic that the
compiler knows about. pow() is well known, ^^ isn't. (Fortran uses **)
It's primarily about syntax sugar: pow() is so ugly. In practice, the
most important case is squaring, which is an extremely common operation.
pow(xxx,2) is horribly ugly for something so fundamental. It's so ugly
that noone uses it: you always change it to xxx * xxx. But then, xxx
gets evaluated twice.
Nice. Meanwhile, I'd like an opSum() operator (∑ range) as well. It's
primarily about syntax sugar: reduce!("a+b")(range) is so ugly. In
practice, the most important case is the sum from 1 to n, which is an
extremely common operation. reduce!("a+b")(iota(1,n+1)) is horribly ugly
for something so fundamental. It's so ugly that noone uses it: you
always change it to n*(n+1)/2. But then, n gets evaluated twice.
Yes, ^^ hasn't been used for exponentiation before. Fortran used **
because it had such a limited character set, but it's not really a
natural choice; the more mathematically-oriented languages use ^.
Obviously C-family languages don't have that possibility.
Well, since D supports unicode, you can always define: alias
reduce!("a+b") ∑;
On a more serious note, I'm starting to think that Phobos needs a specific
convenience function for sum, not because reduce!"a + b" is ugly (it isn't) or
too
much typing (it isn't) but because reduce!"a + b" doesn't work on zero-length
ranges. Obviously, the sum of a zero-length range is zero, but reduce is too
general to know this. This bit me a few times in some code I was debugging last
week. Rather than inserting extra checks or passing an explicit start value in
(which requires you to remember the element type of your range; is it an int or
a
float?), I simply handwrote a sum function and replaced all my reduce!"a + b"
with
sum.
I am all in favor of adding convenience functions sum and product to
phobos. I use them both often enough.
