Re: short-circuit control forms

[Keith Thompson <kst@cts.com>]

"Beard, Frank" <beardf@spawar.navy.mil> writes:
[...]
> It seems to me that the "and" and "or" should have been implemented
> in the short circuit form to begin with, instead of requiring 
> "and then" and "or else".  As soon as one of the conditions is FALSE
> for "and" or TRUE for "or", there is no need to check the remaining
> arguments.

If I were designing a language from scratch, I might do something
like the following:

For an "and" operation, it's unspecified whether the right operand is
evaluated if the left operand is false.  It's also unspecified whether
the left operand is specified if the right operand is false.  Order of
evaluation is unspecified.  Side effects in either operand are
strongly discouraged.  Compilers should do whatever results in the
most efficient generated code.  Most code should use "and" unless
there's a good reason not to.

For an "and then" operation, the left operand is always evaluated; the
right operand is evaluted only if the left operand is true (just like
Ada's "and then").

Finally a third form would specify that both operands are always
evaluated (subject to optimization rules).  Perhaps something like
and(lhs, rhs).

-- 
Keith Thompson (The_Other_Keith) kst@cts.com  <http://www.ghoti.net/~kst>
San Diego Supercomputer Center           <*>  <http://www.sdsc.edu/~kst>
Cxiuj via bazo apartenas ni.