Re: bitwise operators in IDL?

[Craig Markwardt <craigmnet(at)cow.physics.wisc.edu>]

JD Smith <jdsmith@astro.cornell.edu> writes:
> Marc Schellens wrote:
> > To late for short circuitry.
> > Consider a case when the second function in the if case
> > has a side effect (e.g. modifying a global variable).
> > After once defining the language this way, to change it
> > would mean to introduce incopatibility.
> 
> Not if you introduce another operator set all together for short
> circuiting.  People will use them increasingly, and AND,OR will go back
> to being used primarily for their bitwise function, as they should be.  
> Sort of like C has "&&" and "&".  I can't think of good replacement
> names (I assume RSI won't allow the sensible && and ||).  Ideas? (ANDS?
> ORS?).
> 
> JD

I like the idea of short-circuiting logical operators as well.  Some
time ago I proposed LAND and LOR (for Logical-AND and Logical-OR).  Of
course what do you do about backwards compatibility?  Namely people
who have written code with their own LAND or ANDS variables.  Imagine
this :-)

  if LAND LAND 1 then ...

What would it mean?

Also, short-circuiting operators are not well-defined for vector
operands.  With vector operands it is possible in an
element-by-element comparison for one element to evaluate true, while
the other evaluates false.  E.g.

  if [1,1] LAND [0,1] then ...

So, both of these issues would at least have to be dealt with, and my
guess is that the RSI folks will decide not to deal with it.  Still, I
think it's worth exploring.

Craig

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Craig B. Markwardt, Ph.D.         EMAIL:    craigmnet@cow.physics.wisc.edu
Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
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