Re: Comments between lines raise syntax error

[Karim Belabas <Karim.Belabas@u-bordeaux.fr>]

* Ewan Delanoy [2025-11-01 11:07]:
> I have an a small array which I prefer to write line by line for
> readability, and I also would like to insert a few comments in-between
> some lines.

I advise to use { ... } for complicated multi-line statements instead of a
line continuation \. The latter works best for a very small number of lines.

> The following naive trial raises a syntax error in PARI-GP. How can I modify it a little bit to turn it into valid syntax ?
> 
> level4=([\
> 
> e4,\
> 
> /* Level 1 multiplied by Level 3 */
[...]

  {
    level4 = [
    e4,
    /* Level 1 multiplied by Level 3 */
    z1*z5,
    z1*z6,
    z1*z7,
    /* Level 2 multiplied by itself */
    z2*z2,
    z2*z3,
    z3*z3
    ];
  }

N.B.
- I removed the unnecessary parentheses
- I added a ; at the end to suppress output

Cheers

    K.B.

P.S. A trailing = creates a line continuation by itself. Although this
is usually reserved to function definitions. One could equally write

  level4 =
  {
    [
    e4,
    /* Level 1 multiplied by Level 3 */
    z1*z5,
    z1*z6,
    z1*z7,
    /* Level 2 multiplied by itself */
    z2*z2,
    z2*z3,
    z3*z3
    ];
  }

The above is still parsed as

  level4 = [ e4, z1*z5, z1*z6, z1*z7, z2*z2, z2*z3, z3*z3 ];

Other more compact forms are a possibility, such as

  level4 =
  {
    [ e4,
      /* Level 1 multiplied by Level 3 */
      z1*z5, z1*z6, z1*z7,
      /* Level 2 multiplied by itself */
      z2*z2, z2*z3, z3*z3 ];
  }

or

  level4 =
  { [ e4,
      /* Level 1 multiplied by Level 3 */
      z1*z5, z1*z6, z1*z7,
      /* Level 2 multiplied by itself */
      z2*z2, z2*z3, z3*z3 ]; }

Etc.
-- 
Pr. Karim Belabas, U. Bordeaux, Vice-président en charge du Numérique
Institut de Mathématiques de Bordeaux UMR 5251 - (+33) 05 40 00 29 77
http://www.math.u-bordeaux.fr/~kbelabas/