[Q] A really silly question

| a b|
a := 14.
b := - a.
b inspect

is wrong


| a b|
a := 14.
b := 0 - a.
b inspect

is right

Why ?


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To get the negative of a value use

a negated.

Greetz
  Rob

-----Oorspronkelijk bericht-----
Van: [hidden email]
[mailto:[hidden email]] Namens Edgar J. De
Cleene
Verzonden: donderdag 10 mei 2007 19:18
Aan: A friendly place to get answers to even the most basic questions about
Squeak.
Onderwerp: [Newbies] [Q] A really silly question

| a b|
a := 14.
b := - a.
b inspect

is wrong


| a b|
a := 14.
b := 0 - a.
b inspect

is right

Why ?


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El 5/10/07 2:22 PM, "Rob Van Pamel" <[hidden email]> escribió:

> To get the negative of a value use
>
> a negated.
>
> Greetz
>   Rob

Yes, I know that.
What I ask is why you could't do b := - a.


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Hello Edgar,

EJDC> Yes, I know that.
EJDC> What I ask is why you could't do b := - a.

- is a message send. Who should be the receiver?

What's your idea to give this a chance to work?


Cheers,

Herbert                            mailto:[hidden email]

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This is because of the Architecture of Smalltalk ...

It is always so in Smalltalk that you send an message to an object ..
When you do the following

b := 0 - a.

You send the message '-' to the object 0. The parameter of the message is A.

These are called binary messages.
When you have

b := - a

You don't have an object where you send your message to.
Again like I said before when you do a negated you send the message negated
to the object a. I hope you understand it if you don't ask again and I'll
try to explain better

Greetz  

-----Oorspronkelijk bericht-----
Van: [hidden email]
[mailto:[hidden email]] Namens Edgar J. De
Cleene
Verzonden: donderdag 10 mei 2007 19:34
Aan: A friendly place to get answers to even the most basic questions about
Squeak.
Onderwerp: Re: [Newbies] [Q] A really silly question




El 5/10/07 2:22 PM, "Rob Van Pamel" <[hidden email]> escribió:

> To get the negative of a value use
>
> a negated.
>
> Greetz
>   Rob

Yes, I know that.
What I ask is why you could't do b := - a.


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El 5/10/07 2:43 PM, "Rob Van Pamel" <[hidden email]> escribió:

> You don't have an object where you send your message to.

a := - 15

Where you send the message ?






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hey

 a := - 15

Here - 15 is the complete message. But you don't have an object to receive
the message.
In 0 -15. The object who receives the message (- 15)is 0.

That is why a := -15 will not work

-----Oorspronkelijk bericht-----
Van: [hidden email]
[mailto:[hidden email]] Namens Edgar J. De
Cleene
Verzonden: donderdag 10 mei 2007 19:55
Aan: A friendly place to get answers to even the most basic questions about
Squeak.
Onderwerp: Re: [Newbies] [Q] A really silly question




El 5/10/07 2:43 PM, "Rob Van Pamel" <[hidden email]> escribió:

> You don't have an object where you send your message to.

a := - 15

Where you send the message ?






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It's at compiled time no message is send.
-15 is a token
http://blog.3plus4.org/2007/05/06/whats-a-binary-selector/

        Mth



On May 10, 2007, at 7:55 PM, Edgar J. De Cleene wrote:

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El 5/10/07 3:18 PM, "Mathieu Suen" <[hidden email]> escribió:

> It's at compiled time no message is send.
> -15 is a token
> http://blog.3plus4.org/2007/05/06/whats-a-binary-selector/
>
> Mth

At last a good why .
Very, very thanks.

Edgar


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Hello Mathieu,

MS> It's at compiled time no message is send.
MS> -15 is a token
MS> http://blog.3plus4.org/2007/05/06/whats-a-binary-selector/

the original question was
MS> | a b|
MS> a := 14.
MS> b := - a.
MS> b inspect

I believe - a is not parsed as a token here.

Up to now I believed that the Smalltalk compiler does not look at
previous statements to compile a given statement.

Am I wrong here? (no cs background, it's a real question).


Cheers,

Herbert                            mailto:[hidden email]

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nextLiteral

        | prevToken |
        prevToken _ self advance.
        (prevToken == #- and: [token isKindOf: Number])
                ifTrue:
                        [^self advance negated].
        ^prevToken


        Mth



On May 10, 2007, at 8:43 PM, Herbert König wrote:

> Up to now I believed that the Smalltalk compiler does not look at
> previous statements to compile a given statement.

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Hello Mathieu,

MS> | prevToken |
MS> prevToken _ self advance.
MS> (prevToken == #- and: [token isKindOf: Number])
MS> ifTrue:
MS> [^self advance negated].
MS> ^prevToken

imho that doesn't contradict me (at least what I wanted to say :-)

In the example I quoted, the compiler (parser?) would have to look at
the previous line (a := 14.) to know that in the current line
(b := - a.) a is representing a number. Only then it makes sense to
try building a literal.

I was not successful in finding senders of nextLiteral in Scanner or
Parser so I still don't know. Also no luck with searching all sources.

Only hits in xml-parser which is a different beast.


Thanks for your patience anyway!

Herbert                            mailto:[hidden email]

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Oops sorry I missunderstood

of course -a is not parsed as a token but -14 it's

        Mth



On May 10, 2007, at 8:43 PM, Herbert König wrote:

> I believe - a is not parsed as a token here.

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Yes actually I was pointing out the wrong method here  is the good  
one but really ugly(idea is still the same):
scanLitVec
...
                                                [(token == #-
                                                                        and: [((typeTable at: hereChar charCode ifAbsent:  
[#xLetter])) = #xDigit])
                                                                ifTrue:
                                                                        [self scanToken.
                                                                        token _ token negated]]].
...

        Mth



On May 10, 2007, at 9:31 PM, Herbert König wrote:

> I was not successful in finding senders of nextLiteral in Scanner or
> Parser so I still don't know. Also no luck with searching all sources.

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Mathieu Suen a écrit :
- 15 is a job of the parser, not the scanner as early noted by Mathieu.

See http://bugs.squeak.org/view.php?id=3616

It is specific to squeak and does not work in other Smalltalks.
And it is of course interpreted as two different tokens in a literal
array, try #(- 15) = #(-15)

I find it very confusing and already suggested to remove such a feature.
I am happy that Edgar pointed the problem out.

Nicolas

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