JSON.mc4

/* (c) https://github.com/MontiCore/monticore */
package de.monticore.lang;

/* This is a MontiCore stable grammar.
 * Adaptations -- if any -- are conservative. */

/**
 * This grammar describes the JSON language, but it is 
 * a slight superset to the official JSON standard. 
 * It is intended for parsing JSON-compliant artifacts. Further well-formedness
 * checks are not included, because we assume to parse correctly produced JSON 
 * documents only.
 *
 * Please note that JSON (like XML or ASCII) is just a carrier language.
 * The concrete JSON dialect and the question, how to recreate the
 * real objects / data structures, etc. behind the JSON tree structure
 * is beyond this project, but can be applied to the AST defined here.
*/

grammar JSON extends de.monticore.literals.MCCommonLiterals {

  /** An ASTJSONDocument represents an input file in JSON format.
    @attribute jSONValue The top level values contained in the JSON document.
  */
  JSONDocument = JSONValue;

  /** An ASTJSONValue represents an arbitrary property value. */
  interface JSONValue;

  /** An ASTJSONObject is a JSONValue that may contain further properties.
    @attribute props The properties of the JSON document.
  */
  JSONObject implements JSONValue = "{" prop:(JSONProperty || ",")* "}";

  /** An ASTJSONProperty represents elements in a key-value relationship.
    @attribute key The unique identifier of a property.
    @attribute value The property value associated with the identifier.
  */
  JSONProperty = key:String ":" value:JSONValue;

  /** An ASTJSONBoolean represents a boolean property value.
    @attribute booleanLiteral The actual value.
  */
  JSONBoolean implements JSONValue = BooleanLiteral;

  /** An ASTJSONString represents a String property value.
    @attribute stringLiteral The actual value.
  */
  JSONString implements JSONValue = StringLiteral;

  /** An ASTJSONNumber represents a number property value.
    @attribute signedNumericLiteral The actual value (as integer or double).
  */
  JSONNumber implements JSONValue = SignedNumericLiteral;

  /** An ASTJSONArray represents an array of multiple property values.
    @attribute JSONValues The values in the array.
  */
  JSONArray implements JSONValue = "[" (JSONValue || ",")* "]";

  /** An ASTJSONNull represents an empty property value.
    @attribute nullLiteral The actual "null" value.
  */
  JSONNull implements JSONValue = NullLiteral;
  
  /** ASTSignedBasicDoubleLiteral represents a positive or negative double.
    Overrides the inherited production to include exponential representations.
    @attribute source String-representation (including '"').
  */
  SignedBasicDoubleLiteral implements SignedNumericLiteral<1> =
    // to prevent spaces between the optional "-" and the number,
    // we need to define this slightly more complex nonterminal
    // (a pure token would clash with Java tokens if these are added) 
    negative:["-"] DecimalDoublePointLiteral {noSpace()}? | 
                   DecimalDoublePointLiteral;


  /*========================================================================*/
  /*============================= LEXER RULES ==============================*/
  /*========================================================================*/

  // JSON doubles differ from Java doubles in the exponent. 
  // We therefore define a new token here that acts as literal 
  // for JSON

  token DecimalDoublePointLiteral = Digits '.' (Digits)? (ExponentPart)? |
                                    Digits ExponentPart;

  token ExponentPart = ('e' | 'E') ('+' | '-')? Digits;

  
  /*========================================================================*/
  /*=========================== AST DEFINITIONS ============================*/
  /*========================================================================*/

  // because SignedBasicDoubleLiteral is a parsed literal, we add the
  // getSource() and getValue() methods by hand.
  astrule SignedBasicDoubleLiteral =
    method public String getSource() {
      return (isNegative()?"-":"") + getDecimalDoublePointLiteral();
    }
    method public double getValue() {
      return de.monticore.literals.MCLiteralsDecoder.decodeDouble(getSource());
    }
  ;
  
}