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be more specific of where this grammar applies, clean up
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gluaxspeed
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@ -16,154 +16,25 @@
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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; Introduction
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; ------------
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; This file contains an ABNF (Augmented Backus-Naur Form) grammar of Leo string formatting.
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; Background on ABNF is provided later in this file.
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; This grammar provides an official definition of how format strings
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; are parsed for printed by the Leo compiler.
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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; Background on ABNF
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; ------------------
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; ABNF is an Internet standard:
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; see RFC 5234 at https://www.rfc-editor.org/info/rfc5234
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; and RFC 7405 at https://www.rfc-editor.org/info/rfc7405.
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; It is used to specify the syntax of JSON, HTTP, and other standards.
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; ABNF adds conveniences and makes slight modifications
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; to Backus-Naur Form (BNF),
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; without going beyond context-free grammars.
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; Instead of BNF's angle-bracket notation for nonterminals,
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; ABNF uses case-insensitive names consisting of letters, digits, and dashes,
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; e.g. `HTTP-message` and `IPv6address`.
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; ABNF includes an angle-bracket notation for prose descriptions,
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; e.g. `<host, see [RFC3986], Section 3.2.2>`,
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; usable as last resort in the definiens of a nonterminal.
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; While BNF allows arbitrary terminals,
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; ABNF uses only natural numbers as terminals,
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; and denotes them via:
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; (i) binary, decimal, or hexadecimal sequences,
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; e.g. `%b1.11.1010`, `%d1.3.10`, and `%x.1.3.A`
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; all denote the sequence of terminals [1, 3, 10];
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; (ii) binary, decimal, or hexadecimal ranges,
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; e.g. `%x30-39` denotes any singleton sequence of terminals
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; [_n_] with 48 <= _n_ <= 57 (an ASCII digit);
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; (iii) case-sensitive ASCII strings,
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; e.g. `%s"Ab"` denotes the sequence of terminals [65, 98];
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; and (iv) case-insensitive ASCII strings,
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; e.g. `%i"ab"`, or just `"ab"`, denotes
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; any sequence of terminals among
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; [65, 66],
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; [65, 98],
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; [97, 66], and
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; [97, 98].
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; ABNF terminals in suitable sets represent ASCII or Unicode characters.
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; ABNF allows repetition prefixes `n*m`,
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; where `n` and `m` are natural numbers in decimal notation;
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; if absent,
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; `n` defaults to 0, and
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; `m` defaults to infinity.
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; For example,
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; `1*4HEXDIG` denotes one to four `HEXDIG`s,
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; `*3DIGIT` denotes up to three `DIGIT`s, and
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; `1*OCTET` denotes one or more `OCTET`s.
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; A single `n` prefix
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; abbreviates `n*n`,
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; e.g. `3DIGIT` denotes three `DIGIT`s.
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; Instead of BNF's `|`, ABNF uses `/` to separate alternatives.
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; Repetition prefixes have precedence over juxtapositions,
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; which have precedence over `/`.
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; Round brackets group things and override the aforementioned precedence rules,
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; e.g. `*(WSP / CRLF WSP)` denotes sequences of terminals
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; obtained by repeating, zero or more times,
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; either (i) a `WSP` or (ii) a `CRLF` followed by a `WSP`.
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; Square brackets also group things but make them optional,
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; e.g. `[":" port]` is equivalent to `0*1(":" port)`.
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; Instead of BNF's `::=`, ABNF uses `=` to define nonterminals,
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; and `=/` to incrementally add alternatives
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; to previously defined nonterminals.
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; For example, the rule `BIT = "0" / "1"`
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; is equivalent to `BIT = "0"` followed by `BIT =/ "1"`.
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; The syntax of ABNF itself is formally specified in ABNF
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; (in Section 4 of the aforementioned RFC 5234,
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; after the syntax and semantics of ABNF
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; are informally specified in natural language
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; (in Sections 1, 2, and 3 of the aforementioned RFC 5234).
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; The syntax rules of ABNF prescribe the ASCII codes allowed for
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; white space (spaces and horizontal tabs),
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; line endings (carriage returns followed by line feeds),
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; and comments (semicolons to line endings).
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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; Structure
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; ---------
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; This ABNF grammar consists of one grammar:
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; that describes how a Leo string-literal is parsed
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; for formatting.
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; for more info please checkout the
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; [README](./README.md) in this directory.
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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; Format String
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; -------------------
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not-double-quote-or-backslash-or-brace = %x0-21
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/ %x23-5B
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/ %x5D-7A
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/ %x7C
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/ %x7E-10FFFF
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; anything but " or \ or { or }
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; This ABNF grammar consists of one grammar:
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; that describes how a Leo string-literal is parsed
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; for formatting. Meaning in this context
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; all characters are already parsed and we don't
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; have to worry about escapes or etc.
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double-quote = %x22 ; "
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single-quote = %x27 ; '
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single-quote-escape = "\" single-quote ; \'
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double-quote-escape = "\" double-quote ; \"
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backslash-escape = "\\"
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line-feed-escape = %s"\n"
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carriage-return-escape = %s"\r"
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horizontal-tab-escape = %s"\t"
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null-character-escape = "\0"
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simple-character-escape = single-quote-escape
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/ double-quote-escape
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/ backslash-escape
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/ line-feed-escape
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/ carriage-return-escape
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/ horizontal-tab-escape
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/ null-character-escape
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octal-digit = %x30-37 ; 0-7
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hexadecimal-digit = digit / "a" / "b" / "c" / "d" / "e" / "f"
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ascii-character-escape = %s"\x" octal-digit hexadecimal-digit
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unicode-character-escape = %s"\u{" 1*6hexadecimal-digit "}"
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format-string-element-not-brace = not-double-quote-or-backslash-or-brace
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/ simple-character-escape
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/ ascii-character-escape
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/ unicode-character-escape
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not-brace = %x0-7A / %x7C / %x7E-10FFFF ; anything but { or }
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format-string-container = "{}"
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@ -171,9 +42,9 @@ format-string-open-brace = "{{"
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format-string-close-brace = "}}"
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format-string-element = format-string-element-not-brace
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/ format-string-container
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/ format-string-open-brace
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/ format-string-close-brace
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format-string = double-quote *format-string-element double-quote
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format-string-element = not-brace
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/ format-string-container
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/ format-string-open-brace
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/ format-string-close-brace
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format-string = *format-string-element
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