Re: About the primitive macros `and' and `or'

[Yi DAI]

On Fri, Dec 25, 2009 at 4:21 PM, Klaus Schilling <address@hidden> wrote:

As a function, gor needs to have its arguments evaluated before the

actual application takes place, moreover, the order of evaluation is
not specified.

Hence

(define x 0)
(gor (= x 0) (/ x))

gives a numerical overflow error,
whereas

(define x 0)
(or (= x 0) (/ x))

returns true.

If the terms to be evaluated contain non-commutable side effects,
things get out of control, whereas in the macro `or', you may rely on
the order of the side effects.

Yes, Klaus. I forgot that Scheme adopts applicative-order evaluation (after experiencing Haskell for quite a while). 

I do see the necessity of your proposal for normal-order evaluation as default, Stephen, ;)

-- 
DAY