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RE: [Axiom-developer] Convert and Coerce

From: Page, Bill
Subject: RE: [Axiom-developer] Convert and Coerce
Date: Mon, 27 Mar 2006 18:55:36 -0500

On Monday, March 27, 2006 6:36 PM Antoine Hersen wrote
> Just to be sure
> So coercion are done automatically both in a library code
> and in the interpreter.

No. coercion is not done automatically in the library code.
**Only** in the interpreter.

> But conversion need to be forced with "::" both in library
> code and interpreter ?

Yes. Coercion also needs to be forced in the library code,
i.e. in the library code (e.g. SPAD or Aldor) coercion is
treated the same way as conversion.

> So convert imply a lost of information and has to be called 
> explicitely by :: ?

I do not think that in general conversion implies any loss of
information. (I am not sure how to define "loss of information".)
But conversion is often a partial function i.e. only defined for
some members of the domain. For example:


If we only know


it is not "safe" to write:




will fail. Such conversions will not be done automatically.

On the other hand if we know




is always safe and so it is coded as a coercion and done
automatically by the interpreter when needed.

Bill Page.

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