Support for IETF RFC 5234

[egberts]

Just curious, where the computer science industry stand so far on this variant of BNF syntax called IETF RFC5234 for its ABNF syntax scheme?

And whether or not it becomes a worthy feature candidate here.

[egberts]

An example of ABNF is found in the Python community for TOML specification (a solidly used specification by a majority of the Python community) using Github's own ABNF code syntax highlighter below:

https://github.com/toml-lang/toml/blob/1.0.0/toml.abnf

;; This document describes TOML's syntax, using the ABNF format (defined in
;; RFC 5234 -- https://www.ietf.org/rfc/rfc5234.txt).
;;
;; All valid TOML documents will match this description, however certain
;; invalid documents would need to be rejected as per the semantics described
;; in the supporting text description.

;; It is possible to try this grammar interactively, using instaparse.
;;     http://instaparse.mojombo.com/
;;
;; To do so, in the lower right, click on Options and change `:input-format` to
;; ':abnf'. Then paste this entire ABNF document into the grammar entry box
;; (above the options). Then you can type or paste a sample TOML document into
;; the beige box on the left. Tada!

;; Overall Structure

toml = expression *( newline expression )

expression =  ws [ comment ]
expression =/ ws keyval ws [ comment ]
expression =/ ws table ws [ comment ]

;; Whitespace

ws = *wschar
wschar =  %x20  ; Space
wschar =/ %x09  ; Horizontal tab

;; Newline

newline =  %x0A     ; LF
newline =/ %x0D.0A  ; CRLF

;; Comment

comment-start-symbol = %x23 ; #
non-ascii = %x80-D7FF / %xE000-10FFFF
non-eol = %x09 / %x20-7F / non-ascii

comment = comment-start-symbol *non-eol

;; Key-Value pairs

keyval = key keyval-sep val

key = simple-key / dotted-key
simple-key = quoted-key / unquoted-key

unquoted-key = 1*( ALPHA / DIGIT / %x2D / %x5F ) ; A-Z / a-z / 0-9 / - / _
quoted-key = basic-string / literal-string
dotted-key = simple-key 1*( dot-sep simple-key )

dot-sep   = ws %x2E ws  ; . Period
keyval-sep = ws %x3D ws ; =

val = string / boolean / array / inline-table / date-time / float / integer

;; String

string = ml-basic-string / basic-string / ml-literal-string / literal-string

;; Basic String

basic-string = quotation-mark *basic-char quotation-mark

quotation-mark = %x22            ; "

basic-char = basic-unescaped / escaped
basic-unescaped = wschar / %x21 / %x23-5B / %x5D-7E / non-ascii
escaped = escape escape-seq-char

escape = %x5C                   ; \
escape-seq-char =  %x22         ; "    quotation mark  U+0022
escape-seq-char =/ %x5C         ; \    reverse solidus U+005C
escape-seq-char =/ %x62         ; b    backspace       U+0008
escape-seq-char =/ %x66         ; f    form feed       U+000C
escape-seq-char =/ %x6E         ; n    line feed       U+000A
escape-seq-char =/ %x72         ; r    carriage return U+000D
escape-seq-char =/ %x74         ; t    tab             U+0009
escape-seq-char =/ %x75 4HEXDIG ; uXXXX                U+XXXX
escape-seq-char =/ %x55 8HEXDIG ; UXXXXXXXX            U+XXXXXXXX

;; Multiline Basic String

ml-basic-string = ml-basic-string-delim [ newline ] ml-basic-body
                  ml-basic-string-delim
ml-basic-string-delim = 3quotation-mark
ml-basic-body = *mlb-content *( mlb-quotes 1*mlb-content ) [ mlb-quotes ]

mlb-content = mlb-char / newline / mlb-escaped-nl
mlb-char = mlb-unescaped / escaped
mlb-quotes = 1*2quotation-mark
mlb-unescaped = wschar / %x21 / %x23-5B / %x5D-7E / non-ascii
mlb-escaped-nl = escape ws newline *( wschar / newline )

;; Literal String

literal-string = apostrophe *literal-char apostrophe

apostrophe = %x27 ; ' apostrophe

literal-char = %x09 / %x20-26 / %x28-7E / non-ascii

;; Multiline Literal String

ml-literal-string = ml-literal-string-delim [ newline ] ml-literal-body
                    ml-literal-string-delim
ml-literal-string-delim = 3apostrophe
ml-literal-body = *mll-content *( mll-quotes 1*mll-content ) [ mll-quotes ]

mll-content = mll-char / newline
mll-char = %x09 / %x20-26 / %x28-7E / non-ascii
mll-quotes = 1*2apostrophe

;; Integer

integer = dec-int / hex-int / oct-int / bin-int

minus = %x2D                       ; -
plus = %x2B                        ; +
underscore = %x5F                  ; _
digit1-9 = %x31-39                 ; 1-9
digit0-7 = %x30-37                 ; 0-7
digit0-1 = %x30-31                 ; 0-1

hex-prefix = %x30.78               ; 0x
oct-prefix = %x30.6F               ; 0o
bin-prefix = %x30.62               ; 0b

dec-int = [ minus / plus ] unsigned-dec-int
unsigned-dec-int = DIGIT / digit1-9 1*( DIGIT / underscore DIGIT )

hex-int = hex-prefix HEXDIG *( HEXDIG / underscore HEXDIG )
oct-int = oct-prefix digit0-7 *( digit0-7 / underscore digit0-7 )
bin-int = bin-prefix digit0-1 *( digit0-1 / underscore digit0-1 )

;; Float

float = float-int-part ( exp / frac [ exp ] )
float =/ special-float

float-int-part = dec-int
frac = decimal-point zero-prefixable-int
decimal-point = %x2E               ; .
zero-prefixable-int = DIGIT *( DIGIT / underscore DIGIT )

exp = "e" float-exp-part
float-exp-part = [ minus / plus ] zero-prefixable-int

special-float = [ minus / plus ] ( inf / nan )
inf = %x69.6e.66  ; inf
nan = %x6e.61.6e  ; nan

;; Boolean

boolean = true / false

true    = %x74.72.75.65     ; true
false   = %x66.61.6C.73.65  ; false

;; Date and Time (as defined in RFC 3339)

date-time      = offset-date-time / local-date-time / local-date / local-time

date-fullyear  = 4DIGIT
date-month     = 2DIGIT  ; 01-12
date-mday      = 2DIGIT  ; 01-28, 01-29, 01-30, 01-31 based on month/year
time-delim     = "T" / %x20 ; T, t, or space
time-hour      = 2DIGIT  ; 00-23
time-minute    = 2DIGIT  ; 00-59
time-second    = 2DIGIT  ; 00-58, 00-59, 00-60 based on leap second rules
time-secfrac   = "." 1*DIGIT
time-numoffset = ( "+" / "-" ) time-hour ":" time-minute
time-offset    = "Z" / time-numoffset

partial-time   = time-hour ":" time-minute ":" time-second [ time-secfrac ]
full-date      = date-fullyear "-" date-month "-" date-mday
full-time      = partial-time time-offset

;; Offset Date-Time

offset-date-time = full-date time-delim full-time

;; Local Date-Time

local-date-time = full-date time-delim partial-time

;; Local Date

local-date = full-date

;; Local Time

local-time = partial-time

;; Array

array = array-open [ array-values ] ws-comment-newline array-close

array-open =  %x5B ; [
array-close = %x5D ; ]

array-values =  ws-comment-newline val ws-comment-newline array-sep array-values
array-values =/ ws-comment-newline val ws-comment-newline [ array-sep ]

array-sep = %x2C  ; , Comma

ws-comment-newline = *( wschar / [ comment ] newline )

;; Table

table = std-table / array-table

;; Standard Table

std-table = std-table-open key std-table-close

std-table-open  = %x5B ws     ; [ Left square bracket
std-table-close = ws %x5D     ; ] Right square bracket

;; Inline Table

inline-table = inline-table-open [ inline-table-keyvals ] inline-table-close

inline-table-open  = %x7B ws     ; {
inline-table-close = ws %x7D     ; }
inline-table-sep   = ws %x2C ws  ; , Comma

inline-table-keyvals = keyval [ inline-table-sep inline-table-keyvals ]

;; Array Table

array-table = array-table-open key array-table-close

array-table-open  = %x5B.5B ws  ; [[ Double left square bracket
array-table-close = ws %x5D.5D  ; ]] Double right square bracket

;; Built-in ABNF terms, reproduced here for clarity

ALPHA = %x41-5A / %x61-7A ; A-Z / a-z
DIGIT = %x30-39 ; 0-9
HEXDIG = DIGIT / "A" / "B" / "C" / "D" / "E" / "F"

One can use the following to do Github ABNF syntax highlighting:

```abnf
;; Built-in ABNF terms, reproduced here for clarity

ALPHA = %x41-5A / %x61-7A ; A-Z / a-z
DIGIT = %x30-39 ; 0-9
HEXDIG = DIGIT / "A" / "B" / "C" / "D" / "E" / "F"
```

[jacquev6]

Just curious, where the computer science industry stand so far on this variant of BNF syntax called IETF RFC5234 for its ABNF syntax scheme?

I have no idea.

And whether or not it becomes a worthy feature candidate here.

Worthy indeed. I've not worked on this project for a while though, so I'm not going to implement this myself. But I would spend a few hours to merge a PR and deploy it to http://jacquev6.github.io/DrawGrammar. And to OPAM if the process has not changed too much since last time.