astLiteral(ast, retArr) {

    // Reject non numeric literals
    if (isNaN(ast.value)) {
      throw this.astErrorOutput(
        'Non-numeric literal not supported : ' + ast.value,
        ast
      );
    }

    retArr.push(ast.value);

    return retArr;
  }
@desc Parses the abstract syntax tree for *literal value*
@param {Object} ast - the AST object to parse
@param {Array} retArr - return array string
@returns {Array} the append retArr