Vincent Lefevre on Thu, 12 Sep 2024 16:43:34 +0200


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Re: Supporting 2u 

On 2024-09-12 07:17:13 -0700, Ilya Zakharevich wrote:
> On Mon, Aug 12, 2024 at 12:48:46PM +0200, Vincent Lefevre wrote:
> > On 2024-08-12 12:04:36 +0200, Ruud H.G. van Tol wrote:
> > > >    P.S.  IMO, 2u should better be parsed (as expected by the user!).
> > > 
> > > Rather not. For example, 2e1 is already syntax, so can't also mean 2*e1.
> 
> This does not stop other ambiguous syntaxes — like ++.

AFAIK, it isn't ambiguous in GP/PARI, where "++" always means
the increment postfix operator, even with a space:

? x+ +
%1 = x + 1

(I'm wondering whether this is a bug.)

So, this is an error:

? x + +1
  ***   syntax error, unexpected integer, expecting end of file: x++1
  ***                                                               ^-

But this can be confusing for C users:

? x + ++y
%1 = x + (y + 1)

which is actually (x++)+y. So,

? x + ++17
%2 = x + 19
? 17 + ++y
  ***   syntax error, unexpected ++, expecting end of file: 17+++y
  ***                                                          ^---

-- 
Vincent Lefèvre <vincent@vinc17.net> - Web: <https://www.vinc17.net/>
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