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2.2.0 • Public • Published


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grammarkdown is a markdown-style parser for syntactic grammars, designed to make it easily to rapidly prototype a grammar and statically verify its consistency. The grammar supported by grammarkdown is based on the parametric grammar used by ECMA-262 (the JavaScript language standard).


Syntax:                   grammarkdown [options] [...files]

Examples:                 grammarkdown es6.grammar
                          grammarkdown --out es6.md --format markdown es6.grammar

 -f, --format FORMAT      The output format.
 -h, --help               Prints this message.
     --noChecks           Does not perform static checking of the grammar.
     --noEmit             Does not emit output.
     --noEmitOnError      Does not emit output if there are errors.
 -o, --out FILE           Specify the output file.
 -v, --version            Prints the version.


A grammarkdown grammar file uses significant whitespace in the form of line terminators and indentation. Tab (ASCII 0x9) characters are preferred, however using multiple spaces for indentation is supported as long as all nested elements have the same amount of leading whitespace.


A Production consists of a left-hand-side Nonterminal followed by a colon (:) separator and one or more right-hand-side sentences consisting of various forms of terminal and nonterminal symbols. For example:

NameSpaceImport : `*` `as` ImportedBinding

It is recommended that Productions should follow pascal-case naming conventions, to avoid collision with reserved keywords.

You may specify multiple productions for a Nonterminal on multiple lines, as follows:

NamedImports : `{` `}`
NamedImports : `{` ImportList `}`
NamedImports : `{` ImportList `,` `}`

You may also specify multiple left-hand-side sentences for a single production by indenting them:

NamedImports :
    `{` `}`
    `{` ImportList `}`
    `{` ImportList `,` `}`

A Production may specify one or more parameters that can be used to reuse a Nonterminal in various circumstances:

IdentifierReference[Yield] :
    [~Yield] `yield`

A Production may also specify a limited set of terminals, by using the one of keyphrase:

Keyword :: one of
    `break`		`do`		`in`			`typeof`
    `case`		`else`		`instanceof`	`var`
    `catch`		`export`	`new`			`void`
    `class`		`extends`	`return`		`while`
    `const`		`finally`	`super`			`with`
    `continue`	`for`		`switch`		`yield`
    `debugger`	`function`	`this`
    `default`	`if`		`throw`
    `delete`	`import`	`try`


If a Nonterminal on the right-hand-side of a production needs to set a parameter, they supply it in an argument list. Supplying the name of the argument sets the parameter, prefixing the name with a question mark ('?) passes the current value of the parameter, and eliding the argument clears the parameter:

Declaration[Yield] :
    LexicalDeclaration[In, ?Yield]

The right-hand-side of a Production consists of one or more Terminal or Nonterminal symbols, a sentence of Prose, or an Assertion.


A Terminal symbol can be one of the following:

  • A literal string of one or more characters enclosed in backticks ('`'). For example: `function`
  • A sequence of three backtick characters, which denotes a backtick token. For example: ```
  • A unicode character literal enclosed in a leading less-than ('<') character and a trailing greater-than ('>') character. For example: <TAB>


A Nonterminal symbol is an identifier, followed by an optional argument list, and an optional question mark ('?'). The question mark changes the cardinality of the Nonterminal from "exactly one" to "zero or one". The identifier may optionally be enclosed in | characters, if it happens to collide with a keyword.

Character Literals and Ranges

Character literals may be specified using one of the following forms:

  • An abbreviation for a Unicode Code point, of the form <NBSP>
  • A Unicode code point, of the form U+00A0

Character ranges may be specified using the through keyword:

    SourceCharacter but not one of `"` or `\` or U+0000 through U+001F


A sentence of Prose is a single line with a leading greater-than ('>') character. For example: > any Unicode code point

The but not Condition

The but not condition allows you to reference a production, excluding some part of that production. For example:

MultiLineNotAsteriskChar ::
    SourceCharacter but not `*`

Here, MultiLineNotAsteriskChar may contain any alternative from SourceCharacter, except the terminal `*`.

The one of Condition

You can exclude multiple alternatives by including a list of symbols to exclude through the use of the one of keyphrase. Each entry in the list is separated by or:

MultiLineNotForwardSlashOrAsteriskChar ::
    SourceCharacter but not one of `/` or `*`


An Assertion is a zero-width test that must evaluate successfully for the Production to be considered. Assertions are enclosed in a leading open bracket ('[') character and a trailing close-bracket (']') character.

The possible assertions include:

  • The empty assertion, which matches exactly zero tokens: [empty]
  • The lookahead assertion, which verifies the next tokens in the stream: [lookahead != `function`]
  • The no-symbol-here assertion, which verifies the next token is not the provided symbol: [no LineTerminator here]
  • The lexical-goal assertion, which states that the current lexical goal is the supplied Nonterminal: [lexical goal InputElementRegExp]
  • The parameter assertion, which states the supplied parameter to the current production is either set (using the plus ('+') character), or cleared (using the tilde ('~') character): [~Yield] `yield`
  • The prose assertion, which allows for arbitrary prose, mixed with terminals and nonterminals: [> prose text `terminal` prose text |NonTerminal| prose text]

A lookahead assertion has the following operators:

  • The == operator states the lookahead phrase is matched: [lookahead == `class`]
  • The != operator states the lookahead phrase is not matched: [lookahead != `function`]
  • The <- operator states that any matching phrase in the provided set is matched: [lookahead <- { `public`, `private` }]
  • The <! operator states that any matching phrase in the provided set is not matched: [lookahead <! { `{`, `function` }]


During emit, grammarkdown implicitly adds a generated name for each Production and Right-hand side that can be used to link directly to the production using a URI fragment. You can explicitly set the name for a production by tagging it with a custom link name:

Declaration[Yield] :
    HoistableDeclaration[?Yield]       #declaration-hoistable
    ClassDeclaration[?Yield]           #declaration-class
    LexicalDeclaration[In, ?Yield]     #declaration-lexical


You can also annotate your grammar with C-style single-line and multi-line comments.


For comprehensive examples of grammarkdown syntax and output, you can review the following samples:


grammarkdown has an API that can be consumed:

var grammarkdown = require("grammarkdown")
  , Grammar = grammarkdown.Grammar
  , EmitFormat = grammarkdown.EmitFormat
var filename = "...";
var source = "...";
var output;
// parse
var grammar = new Grammar(
  { format: EmitFormat.markdown },
  function () { return source; });
// bind (optional, bind happens automatically during check)
// check (optional, check happens automatically during emit)
// emit
grammar.emit(undefined, function (file, text) { output = text; });



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