Digit separators

Under construction. Digit grouping, Digit separators ADA, Java SE 7, Ruby

Motivation

Permit to write very large integers in source code with line width limit
Enable multi-line/multi-page integers
Enable tracers to write out large integers
Make larger integers more readable
Avoid ad hoc formats

Definition

Replace the syntax productions for

integer
constant

, binary constant, octal constant,

hexadecimal
constant

, float number token, and exponent. Add digit separator.

integer constant (* 6.4.4 *)
   = decimal digit char (* 6.5.2 *),
     { [ digit separator (* 6.4.4 *) ] ,
       decimal digit char (* 6.5.2 *) } ;

binary constant (* 6.4.4 *)
   = binary constant indicator (* 6.4.4 *),
     binary digit char (* 6.5.2 *),
     { [ digit separator (* 6.4.4 *) ] ,
       binary digit char (* 6.5.2 *) } ;

octal constant (* 6.4.4 *)
   = octal constant indicator (* 6.4.4 *),
     octal digit char (* 6.5.2 *),
     { [ digit separator (* 6.4.4 *) ] ,
       octal digit char (* 6.5.2 *) } ;

hexadecimal constant (* 6.4.4 *)
   = hexadecimal constant indicator (* 6.4.4 *),
     hexadecimal digit char (* 6.5.2 *),
     { [ digit separator (* 6.4.4 *) ] ,
       hexadecimal digit char (* 6.5.2 *) } ;

digit separator (* 6.4.4 *)
   = underscore char (* 6.5.2 *),
     [ layout text sequence (* 6.4.1 *) ] ;

float number token (* 6.4.5 *)
   = integer constant (* 6.4.4 *),
     decimal digit char (* 6.5.2 *),
     { decimal digit char (* 6.5.2 *) },
     fraction (* 6.4.5 *),
     [ exponent (* 6.4.5 *) ] ;

exponent (* 6.4.5 *)
   = exponent char (* 6.4.5 *),
     sign (* 6.4.5 *),
     integer constant (* 6.4.4 *) ;
     decimal digit char (* 6.5.2 *),
     { decimal digit char (* 6.5.2 *) } ;

Options

single underscore 1_000 (accepted)
multiple underscores 1__000_000 (undecided)
followed by layout chars 1_ 000 (accepted)
followed by layout text 1_ /* comment */ 000 (accepted)
~~single space for decimals (octal, binary) ISO 31-0 3.3, 80000-1:2009,2022 7.2.1~~ (rejected)
~~multiple spaces for decimals (octal,binary)~~ (rejected)
~~layout chars for decimals (octal, binary)~~ (rejected)
write options?
float support for 1_1.25 ?
float support for 11.2_5 ?
float support for 1.0e1_0 ?

History

2010-11-19 pllib Draft 8 added in 6. Numbers as 6.0 Syntax (digit separator problematic):

digit separator =
    underscore char, [new line char, {layout char}];

2013-01-23 Discussion on SWI list "format/2 Thousands separator"
2013-0?-?? SWI includes 1,3,4,5
2013-05-21 Added to main page (check-in 2013-07-11 as 1.11)

digit separator
   = underscore char (* 6.5.2 *),
     [ layout text sequence (* 6.4.1 *) ] ;
Additionally exactly one space for integer, binary, and octal constant.

2013-12-20 pllib Draft 18 changed to

digit separator =
    underscore char, {layout char}, [new line char, {layout char}];
Note that this uses {layout char}, not [layout text sequence]. This is deliberate; comments are not allowed inside numbers.

2021-06-28 Trealla include 1
2021-08-18 Trealla include 5
2021-11-27 Scryer 1,3,4 but only decimals (#994,#1112)
2025-04-24 Trealla 1,3,4
2025-06-02 WG17 rejects options 5,6,7; accepts options 1,3,4
2025-10-15 Scryer pull request #3125