Re: fetch_user_var() doesn't behave as I expect

[Bill Allombert <Bill.Allombert@math.u-bordeaux.fr>]

On Fri, Jul 14, 2017 at 10:39:55PM +0000, S. Gilles wrote:
> Hi,
> 
> I wanted the following program to print "b=b, c=c", but unfortunately
> it printed "b=b, c=a".
> 
>         #include <pari/pari.h>
>         
>         int main(void)
>         {
>                 pari_init(512 * 1024, 0);
>                 GEN a = varlower("a", 1);
>                 GEN b = gsubst(a, varn(a), varlower("b", 1));
>                 GEN c = gsubst(a, fetch_user_var("a"), varlower("c", 1));
>                 pari_printf("b=%Ps, c=%Ps\n", b, c);
>                 return 0;
>         }
> 
> Based on the manual's description of fetch_user_var(), I think this
> might be a bug, but it is also quite probable that my understanding
> of fetch_user_var() is incorrect.

No, this is correct. Variables created using varlower and fetch_user_var
live in a different namespace.

In library mode, you should rather use fetch_var/delete_var rather than
varlower.

Cheers,
Bill.