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Re: [Axiom-developer] Re: rep, per, Rep in SPAD/Aldor
From: |
Gabriel Dos Reis |
Subject: |
Re: [Axiom-developer] Re: rep, per, Rep in SPAD/Aldor |
Date: |
14 Jul 2007 06:13:19 -0500 |
Ralf Hemmecke <address@hidden> writes:
| Gaby,
|
| just a short reply. As I said, I agree that Rep is an important
| issue. It would actually be good to hear what Stephen Watt has to say
| about that issue. I'd like to learn about the original intentions.
|
| > Secondly, what we want to convey with `rep' is not that one can take
| > object foo, restrict its interpretation at type T and then do an `on
| > faith interpretation of its sequence of bytes representation as an
| > object at type U'. Rather, what we want to say is that object foo
| > at type T is the result of a (hopefully injective) mapping from U
| > and we are interested in its pre-image.
|
| I don't know that I understand that paragraph. If I understand that
| correctly, then (U = Rep, T = %)
|
| per: Rep -> % injective map
| In general we have card(Rep)>=card(%). (If this would not always be
| true then I don't know.)
|
| rep: % -> Rep the "inverse" of per
| If x is from % then rep(x) should be an element from Rep such that
| per(rep x) = x. Since there might be several such elements, rep should
| choose one, and since we want rep to be a function, it should always
| choose the same element from the preimage of per.
|
| Gaby, what you were saying is that Rep and % (in an abstract setting)
| need not be represented by the same string of bytes in memory.
You understand me correctly.
| That is
| my interpretation of your paragraph. Abstractly seen, this seems to be
| OK, but from an efficiency point of view, it is probably always good
| if rep and per actually do nothing than changing the view on the same
| string of bytes in memory.
Depending on the application, yes.
| But, I agree, that decision should be left to the compiler.
-- gaby
- Re: [Axiom-developer] Unions in Spad, (continued)
- Re: [Axiom-developer] Unions in Spad, Ralf Hemmecke, 2007/07/13
- Re: [Axiom-developer] Unions in Spad, Ralf Hemmecke, 2007/07/13
- Re: [Axiom-developer] Unions in Spad, Stephen Wilson, 2007/07/13
- Re: [Axiom-developer] Unions in Spad, Stephen Wilson, 2007/07/13
- Re: [Axiom-developer] Unions in Spad, Gabriel Dos Reis, 2007/07/13
- rep, per, Rep in SPAD/Aldor, was: Re: [Axiom-developer] Unions in Spad, Ralf Hemmecke, 2007/07/13
- Re: rep, per, Rep in SPAD/Aldor, was: Re: [Axiom-developer] Unions in Spad, Gabriel Dos Reis, 2007/07/13
- [Axiom-developer] Re: rep, per, Rep in SPAD/Aldor, Ralf Hemmecke, 2007/07/13
- [Axiom-developer] Re: rep, per, Rep in SPAD/Aldor, Gabriel Dos Reis, 2007/07/14
- [Axiom-developer] Re: rep, per, Rep in SPAD/Aldor, Ralf Hemmecke, 2007/07/14
- Re: [Axiom-developer] Re: rep, per, Rep in SPAD/Aldor,
Gabriel Dos Reis <=
- [Axiom-developer] Re: [Aldor-l] rep, per, Rep in SPAD/Aldor, Christian Aistleitner, 2007/07/14
- Re: [Axiom-developer] Unions in Spad, Ralf Hemmecke, 2007/07/13
- Re: [Axiom-developer] Unions in Spad, Stephen Wilson, 2007/07/13
Re: [Axiom-developer] Unions in Spad, Bill Page, 2007/07/08
Re: [Axiom-developer] Unions in Spad, Waldek Hebisch, 2007/07/09
Re: [Axiom-developer] Unions in Spad, Bill Page, 2007/07/09