Re: [Axiom-developer] PATCH : retrieval of Stream from a KAF file

[Vanuxem Gregory]

Le vendredi 17 novembre 2006 à 21:50 +0100, Waldek Hebisch a écrit :
> > Hello,
> > 
> > Here is a small patch that fixes the incorrect retrieval of some Streams
> > from a KAF file. It replaces 'EQ' by 'EQUAL' for comparisons of strings.
> > There are some other unmodified uses of EQ in this file. They need
> > further investigations and in particular I need to look at what I
> > consider a big issue : equality with object of type 'Any' (I postponed
> > my work on Stream).
> > 
> > --- src/algebra/stream.spad.pamphlet.old    2006-11-17 16:59:13.000000000
> > +0100
> > +++ src/algebra/stream.spad.pamphlet        2006-11-17 17:24:39.000000000 
> > +0100
> > @@ -647,8 +647,8 @@
> >  
> >      Rep := Record(firstElt: S, restOfStream: %)
> >  
> > -    explicitlyEmpty? x == EQ(frst x,NullStream)$Lisp
> > -    lazy? x            == EQ(frst x,NonNullStream)$Lisp
> > +    explicitlyEmpty? x == EQUAL(frst x,NullStream)$Lisp
> > +    lazy? x            == EQUAL(frst x,NonNullStream)$Lisp
> >  
> >  --% signatures of local functions
> >  
> > 
> 
> That looks strange for me. NullStream and NonNullStream should be
> unique objects, so I would probably turn them into symbols.  Your
> change would make a one element list:

This is because NullStream and NonNullStream are globales variables
(NullStream is a macro (NullStream ==> $NullStream$Lisp)) but when you
store a Stream and retrieve it a new string is created and therefore
these strings do not share their memory locations. I do not understand
why you say "Your change would make a one element list", they are just
strings.

If you want )trace STREAM and restore a '[]::Stream(PI)', you'll see:

  1<enter Stream.explicitlyEmpty?,12 : ("NullStream")
   1<enter Stream.frst,10 : ("NullStream")
   1>exit  Stream.frst,10 : "NullStream"
  1>exit  Stream.explicitlyEmpty?,12 : NIL

This is because they do not share the same memory location. The output
of Stream.explicitlyEmpty? has to be T.

Greg