On 16 juil. 2014, at 11:12, Max Bareis <info@derverkoster.de> wrote:

The misunderstanding her is based in the error message of the ui.
when you write 
^ - self width.
and save, the UI writes this text into the code:
^ only numbers may be negated ->- self width.

More helpful would have been something like: �only literals may be negated with - use <object> negated instead�.
I was irritated and on the wrong track because I was absolutely sure that self width is a number.

You are right, the error message should be better. 
I opened a bug entry and submitted a slice with the new error message: "The '-' prefix works only for literal numbers (use #negated instead)". 
https://pharo.fogbugz.com/f/cases/13568/Better-error-message-when-using-prefix  

Regards

Max

Am 16.07.2014 um 10:44 schrieb Alain Busser <alain.busser@gmail.com>:

That's where the Inspector comes in:

To debug, it is good to insert a self width inspect so that the inspector opens up and reveals what exactly the width is. OK, it is a number; then open the browser and look at the number's methods; or in the finder, try 2 . -2 in the examples...

Pharo is excellent at debugging, that is why I choosed it for my Ontology project, the browser shows welle what is a number, what kind of numbers there are, and why a complex number is not a number...

Alain


On Wed, Jul 16, 2014 at 2:59 AM, Verkoster Info <info@derverkoster.de> wrote:

It definitely is,

 
 
 
thanks for all your answers�
 
Regards
 
Max
 
Am 16.07.2014 um 00:56 schrieb Camille Teruel <camille.teruel@gmail.com>:

I've been overtaken :)
Isn't that an active mailing list ? 


On 16 juil. 2014, at 00:53, Camille Teruel <camille.teruel@gmail.com> wrote:

Hi Max,
 
Pharo doesn't have syntax for prefix operator like "-". 
The parser does accepts a "-" before literal numbers but it's not possible for arbitrary expressions.
However you have the message #negated .
 
negatedWidth
 ^ self width negated
 
Cheers,
Camille

On 16 juil. 2014, at 00:16, Verkoster Info <info@derVerkoster.de> wrote:

Hi,

I am using latest Pharo 3.0 + vm.

I have a method width with
width

^ 115 * self ratio.
in my understanding it returns a Number.

When I try to create a method
negatedWidth

^   - (self width).

the UI tells me that only Numbers may be negated. I am not able to save the method. Am I on a wrong path or should that work and if how can I avoid the UI error message?

Regards

Max