From: "Jürgen Strobel" <strobel@...>
Date: 2006-09-01T15:10:53+09:00
Subject: Re: and and or priority

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On Thu, Aug 31, 2006 at 03:01:26AM +0900, Rick DeNatale wrote:
> On 8/30/06, J=FCrgen Strobel <strobel@secure.at> wrote:
> >On Tue, Aug 29, 2006 at 08:55:09AM +0900, Michael W. Ryder wrote:

> >I wouldn't say it is wrong the way ruby does it, but not exactly
> >intuitive either. Choosing to follow english language rather than
> >widespread convention *and* similiar constructs in ruby itself (&&,
> >||, +, *, ...) may seem a bit ... anti POLS.
>=20
> A perl programmer would be very surprised if AND, OR, && and || worked
> any other way.  Probably the most common perl idiom here is:
>=20
>     "some long complicated expression" or die

That's not a complete example, as no precedence rules come into play
here. and and or are pretty low-precedence operators in perl and ruby
alike, which makes constructs like the above possible without
parenthesises.  But what I am driving at is this:

irb(main):035:0> 1 + 2 * 6
=3D> 13
irb(main):036:0> 1 | 2 & 6
=3D> 3
irb(main):037:0> 1 | (2 & 6)
=3D> 3
irb(main):038:0> (1 | 2) & 6
=3D> 2

Clearly, & binds stronger than |, same as * binds stronger than +.
(In a boolean algebra those operations are the same
respectively).

irb(main):073:0> def pr(x) p x; x; end
=3D> nil

irb(main):076:0> (pr 1) || (pr 2) && (pr 3)
1
=3D> 1
irb(main):077:0> (pr 1) or (pr 2) and (pr 3)
1
3
=3D> 3

In the first case, && binds stronger than ||, but is short circuited
away. In the second case "and" does not bind stronger than "or", which
suprised me, given prior knowledge. Is it really only me?

-J=FCrgen

--=20
 The box said it requires Windows 95 or better so I installed Linux

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