Prevent cloning of clones

[Adde]

Thanks! I was just trying to understand when and how to limit further 
cloning.
Following your suggestions i came up with the following:

SVG ensureDelegatedNamespace: #Units.
SVG Units addImmutableSlot: #Pixel valued: (BaseUnit name: 'pixel' 
abbrev: 'px').

n@(Number traits) px [
  n with: px
].

uv@(UnitValue traits) toXML [
  (uv value toXML) ; (uv unit abbrev toXML)
].

s@(String traits) toXML [
 s
].

n@(Number traits) toXML [
  n as: String
].

I added the px method to Number traits to be able to say: 1 px instead 
of 1 with: px, don't know if that's a good idea but it certanly makes it 
easier to use. The other methods are just placeholder for XML-specific 
formatting.
I plan on changing the toXML methods into printOn: s@(XMLStream) to 
match the rest of the environment better.
I feel a bit unsure about the method on UnitValue traits, it feels like 
I should only provide toXML for my own UnitValues, something like this:

SVG addPrototype: #Unit derivedFrom: {BaseUnit}.
SVG Unit addImmutableSlot: #Pixel valued: (SVG Unit name: 'pixel' 
abbrev: 'px').
SVG addPrototype: #UnitValue derivedFrom: {UnitValue}.

uv@(UnitValue traits) unit: u@(SVG Unit traits) value: v [
  SVG UnitValue clone `>> [unit: u. value: v.]
].

uv@(SVG UnitValue traits) toXML [
  (uv value toXML) ; (uv unit abbrev toXML)
].

At least that works as it should, "(1 px) toXML" works and "(1 kg) 
toXML" gives an error.

I have to say the language feels good so far, it strikes a fine balance 
between the beauty of Smalltalk and the raw power of Lisp.

/Adde

Brian Rice wrote:

> On Apr 25, 2005, at 1:43 PM, Brian Rice wrote:
>
>> I strongly suggest that you just forget about this issue and don't 
>> worry about the safety factor for now. Focus on the real design 
>> issues first; your code is a mess and is not re-using the very useful 
>> library I mentioned above. Try this instead:
>>
>> load: 'src/lib/dimensioned.slate'.
>> SVG addImmutableSlot: #Pixel valued: (BaseUnit name: 'pixel' abbrev: 
>> 'px').
>>
>> Doesn't that look better? It also can be used for actual algebraic 
>> operations, e.g.:
>>
>> Slate> BaseUnit name: 'pixel' abbrev: 'px'.
>> px
>> Slate> 4 with: pixel.
>> 4_px
>> Slate> it * 5.
>> 20_px
>> Slate> it / (1 with: in).
>> 20_px/in
>
>
> And if you define:
>
> x@(UnitValue traits) / y@(Unit traits)
> [x / (1 with: y)].
>
> Then "(72 with: px) / in" works. I'll add that now to the main source 
> tree.
>
>> The underscores are not really suitable for output into XML, but you 
>> can easily do something different there, or we could fix the 
>> print-out or provide some other means. In any case, you have 
>> multi-dispatch and can handle the case specifically in any output 
>> method.
>
>
>
>
> -- 
> Brian T. Rice
> LOGOS Research and Development
> http://tunes.org/~water/
>