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Bill Allombert on Mon, 08 May 2023 17:22:14 +0200
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Re: boolean values for [] and List()
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- To: pari-users@pari.math.u-bordeaux.fr
- Subject: Re: boolean values for [] and List()
- From: Bill Allombert <Bill.Allombert@math.u-bordeaux.fr>
- Date: Mon, 8 May 2023 17:20:56 +0200
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On Mon, May 08, 2023 at 10:55:16AM -0400, Max Alekseyev wrote:
> Why is there a discrepancy between empty vector and empty list?
>
> ? if([], print("yes"), print("no"))
> no
> ? if(List(), print("yes"), print("no"))
> yes
This is because List() is not an arithmetic type: List()-List() is not defined:
? List()-List()
*** at top-level: List()-List()
*** ^-------
*** _-_: forbidden addition t_LIST + t_LIST.
so it is not subject to the 'x-x == 0' rule.
But in both case, it is better to do
if(#[],...)
if(#List(),...)
Cheers,
Bill.