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# Numeric separator syntax

Numeric separator syntax is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

Several programming languages allow separators in numerals in order to group digits together.

Show the numeric separator syntax and describe its specification. E.g., what separators are eligible? Can there be multiple consecutive separators? What position can a separator be in? Etc.

## ALGOL 68

In Algol 68, spaces are not significant in identifiers or numeric literals. This allows spaces to be used as numeric separators.
Single or multiple spaces can be used as desired, it is not necessary to group the digits into blocks of three.

`BEGIN    INT  a = 1 234 567;    REAL b = 3      .    1 4159 26 5 359;    print( ( whole( a, 0 ), "  ", fixed( b, - 14, 11 ), newline ) )END `
Output:
```1234567   3.14159265359
```

## AWK

` # syntax: GAWK -f NUMERIC_SEPARATOR_SYNTAX.AWK# converted from ALGOL 68BEGIN {# AWK lacks numeric separators but can be simulated using white space.    a = 1 234 567    b = 3  "."  1 4159 26 5 359    print(a,b)    exit(0)} `
Output:
```1234567 3.14159265359
```

## C

locale.h provides Localization functions and is part of the C Standard Library. Separating digits in code text is not possible.

` #include <locale.h>#include <stdio.h> int main(){  unsigned long long int trillion = 1000000000000;   setlocale(LC_NUMERIC,"");   printf("Locale : %s, One Trillion : %'llu\n", setlocale(LC_CTYPE,NULL),trillion);   return 0;} `

Output :

```[[email protected]:~/doodles \$ ./a.out
Locale : C, One Trillion : 1,000,000,000,000
```

## Factor

Factor allows the comma `,` as a separator character in number literals.

`USE: prettyprint 12,345 .   ! 12345 ! commas may be used at arbitrary intervals1,23,456,78910 .  ! 12345678910 ! a comma at the beginning or end will parse as a word, likely causing an error! ,123 .   ! No word named “,123” found in current vocabulary search path! 123, .   ! No word named “123,” found in current vocabulary search path ! likewise, two commas in a row will parse as a word! 1,,23 .   ! No word named “1,,23” found in current vocabulary search path ! There are no exceptions to which numbers may have separators! binary/octal/decimal/hexadecimal integers and floats are supported0b1,000,001 .   ! 65-1,234e-4,5 .   ! -1.234e-420x1.4,4p3 .   ! 10.125 ! as are ratios45,2+1,1/43,2 .   ! 452+11/4321,1/1,7 .   ! 11/17 ! and complex numbersC{ 5.225,312 2.0 } .   ! C{ 5.225312 2.0 }`

If one desires to define a syntax for different separator rules, that is possible:

`USING: lexer math.parser prettyprint sequences sets ; << SYNTAX: PN: scan-token "_" without string>number suffix! ; >> ! permissive numbersPN: _1_2_3_ .   ! 123PN: 1__234___567 .   ! 1234567PN: 0b0___10.100001p3 .   ! 20.125`

Since Factor's parser is exposed, one could even make changes to the number parser, obviating the need for parsing words.

`USING: eval prettyprint ; << "IN: math.parser.privateUSE: combinators: @pos-digit-or-punc ( i number-parse n char -- n/f )    {        { 95 [ [ @pos-digit ] require-next-digit ] }   ! normally 44        { 43 [ ->numerator ] }        { 47 [ ->denominator ] }        { 46 [ ->mantissa ] }        [ [ @pos-digit ] or-exponent ]    } case ; inline" eval( -- ) >> 3_333_333 .   ! 3333333`

## Go

From version 1.13, Go supports underscores as digit separators for numeric literals. An underscore may appear between any two digits or between the literal prefix (0b, 0o, 0x) and the first digit.

Using the Raku examples plus a few more which Go allows:

`package main import "fmt" func main() {    integers := []int{1_2_3, 0b1_0_1_0_1, 0xa_bc_d, 0o4_37, 0_43_7, 0x_beef}    for _, integer := range integers {        fmt.Printf("%d  ", integer)    }    floats := []float64{1_2_3_4.2_5, 6.0_22e4, 0x_1.5p-2}    for _, float := range floats {        fmt.Printf("%g  ", float)    }    fmt.Println()    // none of these compile    // floats2 := []float64{_1234.25, 1234_.25, 1234._25, 1234.25_, 12__23.25}}`
Output:
```123  21  43981  287  287  48879  1234.25  60220  0.328125
```

## Java

Underscores have to be located within digits. The number of underscores and their position is not restricted.

`  public class NumericSeparatorSyntax {     public static void main(String[] args) {        runTask("Underscore allowed as seperator", 1_000);        runTask("Multiple consecutive underscores allowed:", 1__0_0_0);        runTask("Many multiple consecutive underscores allowed:", 1________________________00);        runTask("Underscores allowed in multiple positions", 1__4__4);        runTask("Underscores allowed in negative number", -1__4__4);        runTask("Underscores allowed in floating point number", 1__4__4e-5);        runTask("Underscores allowed in floating point exponent", 1__4__440000e-1_2);        //runTask(_100);  does not compile - cannot be before first digit        //runTask(100_);  does not compile - cannot be after last digit        //runTask(144_.25);  does not compile - must be within digits        //runTask(144._25);  does not compile - must be within digits    }     private static void runTask(String description, long n) {        runTask(description, n, "%d");    }     private static void runTask(String description, double n) {        runTask(description, n, "%3.7f");    }     private static void runTask(String description, Number n, String format) {        System.out.printf("%s:  " + format + "%n", description, n);    } } `
Output:
```Underscore allowed as seperator:  1000
Multiple consecutive underscores allowed::  1000
Many multiple consecutive underscores allowed::  100
Underscores allowed in multiple positions:  144
Underscores allowed in negative number:  -144
Underscores allowed in floating point number:  0.0014400
Underscores allowed in floating point exponent:  0.0000144
```

## Julia

Julia allows use of the underscore _ as a digit separator. The _ separator must be preceded and followed by a digit. Commas are not allowed in numeric literals.

`     julia> 2_9    29     julia> 2_9_9_0    2990     julia> 2_9_9.0_01    299.001     julia> 1._01    ERROR: syntax: invalid numeric constant "1._"     julia> -1_0    -10     julia> -_10    ERROR: UndefVarError: _10 not defined    Stacktrace:     [1] top-level scope at none:0     julia> 0x34_ff    0x34ff     julia> 0x_34ff    ERROR: syntax: invalid numeric constant "0x_"     julia> 10_000_000    10000000     julia> 10__000__000    ERROR: UndefVarError: __000__000 not defined `

## OCaml

Underscores can be used as separators in integer or floating-point literals, and they are ignored. Underscores can be in any position except at the beginning, and you can use consecutive underscores.

`Printf.printf "%d\n" 1_2_3;; (* 123 *)Printf.printf "%d\n" 0b1_0_1_0_1;; (* 21 *)Printf.printf "%d\n" 0xa_bc_d;; (* 43981 *)Printf.printf "%d\n" 12__34;; (* 1234 *)Printf.printf "%f\n" 1_2_3_4.2_5;; (* 1234.250000 *)Printf.printf "%f\n" 6.0_22e4;; (* 60220.000000 *)Printf.printf "%f\n" 1234_.25;; (* 1234.250000 *)Printf.printf "%f\n" 1234._25;; (* 1234.250000 *)Printf.printf "%f\n" 1234.25_;; (* 1234.250000 *)`

## Perl

Perl allows underscore as a grouping / separator character in numeric inputs, as long as you use it between digits, and you do not use two underscores in a row:

`# Intprint 1_2_3, "\n";  # 123 # Binary Intprint 0b1_0_1_0_1, "\n"; # 21 # Hexadecimal Intprint 0xa_bc_d, "\n"; # 43981 # Ratprint 1_2_3_4.2_5, "\n"; # 1234.25 # Numprint 6.0_22e4, "\n"; # 60220`

## Phix

Phix simply ignores underscores in numeric literals, however a leading underscore signifies a normal identifier, much like a123 or tmp2.
Commas are not allowed in numeric literals, since they delimit sequence elements, routine parameters, and such like, for example {1,2,3,4}.

`? 1_2_3          -- 123--? _1234.25    -- undefined identifier _1234? 0b1_0_1_0_1   -- 21? 0b_1_0_1_0_1  -- 21? 0xa_bc_d      -- 43981? #_DEAD_BEEF_  -- 3735928559.0? 0x_dead_beef  -- 3735928559.0? 3.14_15_93    -- 3.141593? 1_2_3_4.2_5   -- 1234.25? 1234_.25      -- 1234.25? 1234._25      -- 1234.25? 1234.25_      -- 1234.25? 12__34.25     -- 1234.25? 6.0_22e4      -- 60220`

## Python

Works with: Python version 3.6+

The Syntax for separators in numbers, (numeric literals), is given here in the Python documentation.

• The underscore, '_', is used as a separator.
• Single underscores can be used to separate digits or can occur after base specifiers.

## Racket

Vanilla Racket does not have numeric separator syntax. However, it can be defined by users. A quick solution is to use `#%top`:

`#lang racket (require syntax/parse/define         (only-in racket [#%top racket:#%top])         (for-syntax racket/string)) (define-syntax-parser #%top  [(_ . x)   #:do [(define s (symbol->string (syntax-e #'x)))         (define num (string->number (string-replace s "_" "")))]   #:when num   #`#,num]  [(_ . x) #'(racket:#%top . x)]) 1_234_567.891_234__567.89`
Output:
```1234567.89
1234567.89
```

In the above implementation of the syntax, `_` is the separator. It allows multiple consecutive separators, and allows the separator anywhere in the numeral (front, middle, and back).

Implementation details: any token with `_` is considered an identifier in vanilla Racket. If it's not defined already, it would be unbound. We therefore can define `#%top` to control these unbound identifiers: if the token is a number after removing `_`, expand it to that number.

If we wish to, for example, disallow multiple consecutive separators like `1_234__567.89`, we could do so easily:

`#lang racket (require syntax/parse/define         (only-in racket [#%top racket:#%top])         (for-syntax racket/string)) (define-syntax-parser #%top  [(_ . x)   #:do [(define s (symbol->string (syntax-e #'x)))         (define num (string->number (string-replace s "_" "")))]   #:when num   (syntax-parse #'x     [_ #:fail-when (string-contains? s "__") "invalid multiple consecutive separators"        #`#,num])]  [(_ . x) #'(racket:#%top . x)]) 1_234_567.891_234__567.89`
Output:
```1_234__567.89: invalid multiple consecutive separators in: 1_234__567.89
```

A more complicated solution is to create a new language that changes Racket's reader. One approach is to adjust the readtable to recognize the new number literals so that we don't need to change the whole reader. While being slightly more complicated, this solution is better in a sense that `(read)` will also recognize the new number literals.

## Raku

(formerly Perl 6) Raku allows underscore as a grouping / separator character in numeric inputs, though there are a few restrictions.

`# Any numeric input value may use an underscore as a grouping/separator character.# May occur in nearly any position, in any* number. * See restrictions below. # Intsay 1_2_3;  # 123 # Binary Intsay 0b1_0_1_0_1; # 21 # Hexadecimal Intsay 0xa_bc_d; # 43981 # Ratsay 1_2_3_4.2_5; # 1234.25 # Numsay 6.0_22e4; # 60220 # There are some restrictions on the placement.# An underscore may not be on an edge boundary, or next to another underscore.# The following are all syntax errors. # say _1234.25;# say 1234_.25;# say 1234._25;# say 1234.25_;# say 12__34.25;`

## REXX

The REXX language doesn't allow commas (or other separators) in decimal numbers   (for input),   commas are considered argument separators   (if used from within a program,   or as (passed/invoked) arguments from any program).

However, for   binary   and   hexadecimal numbers,   (multiple) blanks are allowed in appropriate places.

For   binary   numbers,   blanks are allowed between groups of four binary digits.

For example:

```   '1101 1001'B
'1101 1001'b
"1111 0101 0011 0010"B
'111 0101 1110'b       is the same as  '0111 0101 1110'b
```

For example:

```   'de ad    be ef 'x
"08 09 0A"X
'789 cc'x               is the same as   '07 89 CC'x
```

For   decimal   numbers,   blanks are allowed between the sign (if present) and the numeric part of the number.
Optional, blanks are allowed before the sign,   and also after the number.

For example:

```   + 4500
-   1719
```

There is a way to work around such that blanks or commas could be used within a REXX program with a bit of coding:

`pi= 3 . 14159 26535 89793 23846 26433 83279 50288 41971 69399 37510 58209 74945pi= 3 . 14159_26535_89793_23846_26433_83279_50288_41971_69399_37510_58209_74945pi = space( translate(pi, , ",_"), 0)`

─── where the last REXX statement will translate (change) any number of separator characters into blanks,   and
remove all blanks from the "number".

## Ruby

Ruby supports one separator, the underscore. It behaves like Perl's underscore.

## Scala

Since Scala 2.13.0 it's stated in the Scala Language Specification that: "The digits of a numeric literal may be separated by arbitrarily many underscores for purposes of legibility." Let's see how its work in a Scala REPL session:

`Welcome to Scala 2.13.0 (Java HotSpot(TM) 64-Bit Server VM, Java 12.0.2).Type in expressions for evaluation. Or try :help. scala> // Integer Literals scala> // Using _ as a digit separator (neither leading nor trailing) it can be placed anywhere in the number. scala> 1_2_3res0: Int = 123 scala> 0xa_bc_dres1: Int = 43981 scala> 0x_dead_beefres2: Int = -559038737 scala> 1_2_3_4.2_5res3: Double = 1234.25 scala> 6.0_22e4res4: Double = 60220.0 scala> 12__34.25res5: Double = 1234.25 scala>`

## Sidef

Sidef allows underscores as a separator character in numeric inputs.

`# Intsay 1_2_3;  # 123 # Binary Intsay 0b1_0_1_0_1; # 21 # Hexadecimal Intsay 0xa_bc_d; # 43981 # Rationalsay 1_2_3_4.2_5; # 1234.25 # Rational in exponential notationsay 6.0_22e4; # 60220 # Apart from starting the number with an underscore, can be placed anywhere in the number. say 1234_.25;       # 1234.25say 1234._25;       # 1234.25say 1234.25_;       # 1234.25say 12__34.25;      # 1234.25# say _1234.25;     # syntax error`

## XPL0

Numbers can contain underlines, which is useful for making long strings of digits easier to recognize. Underlines in coded constants are simply ignored by the parser. Underlines in numbers typed in to a running program are also ignored.

`def Meg = 1_000_000;[IntOut(0, Meg);  CrLf(0);RlOut(0, 123__45.67_89_);  CrLf(0);HexOut(0, \$ABCD_EF01);  CrLf(0);HexOut(0, %1010_1011_1100_1101_1110_1111_0000_0001);  CrLf(0);IntOut(0, IntIn(0));]`
Output:
```1000000
12345.67890
ABCDEF01
ABCDEF01
-321_00__0_
-321000
```

## Wren

Library: Wren-fmt

Consistent with its C heritage, Wren doesn't support any form of separator in numeric literals. However, it's possible using the Wren-fmt module to add any single character 'thousands' separator when 'stringifying' an integer as the example below shows.

As currently written, this just supports separation of decimal integers into 3 digit groups from the right though it could be extended to deal with other scenarios as well.

`import "/fmt" for Fmt var nums = [1e6, 1e9, 123456789, -123456789012]var seps = [",", ".", " ", "*"]for (i in 0...nums.count) System.print(Fmt.commatize(nums[i], seps[i]))`
Output:
```1,000,000
1.000.000.000
123 456 789
-123*456*789*012
```

## zkl

`For source code, integers and floats allow a "_" between digits (or trailing)and completely ignores them:    1_000 == 1_000_ == 1_0_0_0 == 1__________000   1_2.3_4 == 12.34For hex, both "_" and "|" are allowed: 0x12|34`
`For printing, the String.fmt method will add separators for %d (interger: ","), %f (float: ","), %x (hex: "|") and %2B (binary: "|")."%,d  %,.0f  %,x  %,.2B".fmt(1234, 1234.0, 0x1234, 0x1234).println();   --> "1,234  1,234  12|34  1|0010|0011|0100"Each objects toString method has optional parameters to specify a separator and "column width". This method is called (by fmt) for the above tags.`