Re: precedence

[John W. Eaton]

On  6-Aug-2002, Paul Kienzle <address@hidden> wrote:

| On Tue, Aug 06, 2002 at 12:40:23PM -0500, John W. Eaton wrote:
|
| >   * In Matlab, element-wise AND (&) has higher precedence than
| >     element-wise OR (|), in Octave they have the same precedence.
| > 
| >   * In Matlab, short-circuit AND (&&) has higher precedence than
| >     short-circuit OR (||), in Octave they have the same precedence.
| 
| I use parentheses when mixing "and" and "or" in an expression so
| that I don't have to think about precedence, so this won't affect me.
| 
| I believe matlab's precedence corresponds to the usual convention
| in logic so I suppose it is a better choice.  
| 
| You might consider warning users if they have mixed "and" and "or" in the
| same expression.

OK, I've checked in a change to the CVS archive that changes the
precedence for ||, &&, |, and & to match Matlab.  Octave will now also
warn when expressions like

  x | y && z  ==>  x | (y & z) now, previously (x | y) & z

or

  x || y && z  ==>  x || (y && z) now, previously (x || y) && z

appear.  There should be no change if & or && appears first, because
previously, the precedence of & and | was the same, and the precedence
of && and || was the same.  Given the left associativity, they would
group the same before as now.

You can turn the warning off by using parens or by setting the new
built-in variable warn_precedence_change to 0 (the default is 1).

The transpose operator precedence fix will take a bit more work.

jwe



-------------------------------------------------------------
Octave is freely available under the terms of the GNU GPL.

Octave's home on the web:  http://www.octave.org
How to fund new projects:  http://www.octave.org/funding.html
Subscription information:  http://www.octave.org/archive.html
-------------------------------------------------------------