EBNF.sdf

module languages/ebnf/syntax/EBNF

%% Simple Extended Backus-Naur Form (EBNF) notation for describing
%% context-free grammar. This notation is very close to the notation
%% as used in W3C standards

imports
  basic/Identifiers
  basic/Strings
exports
  context-free start-symbols
    Grammar
  sorts Grammar Rule Expression HexChar CharRange CharClass
  lexical syntax
    "#x" [0-9A-Fa-f]+                 -> HexChar
    HexChar "-" HexChar               -> CharRange
    HexChar                           -> CharRange
    "[" CharRange* "]"                -> CharClass            %% Character class
    "[" "^" CharRange* "]"            -> CharClass            %% Negated character class
  context-free syntax
    Rule*                             -> Grammar              %% Complete grammar
    IdCon "::=" Expression            -> Rule                 %% Grammar rule
    IdCon                             -> Expression           %% Non-terminal
    String                            -> Expression           %% Literal
    "(" Expression ")"                -> Expression {bracket} %% Grouping
    Expression "?"                    -> Expression           %% Optional
    Expression "*"                    -> Expression           %% Zero or more repetitions
    Expression "+"                    -> Expression           %% One or more repetitions
    Expression "|" Expression         -> Expression {left}    %% Alternative operator
    Expression Expression             -> Expression {left}    %% Sequential composition
    
  context-free priorities
    Expression Expression -> Expression {left} >
    Expression "|" Expression  -> Expression {left}