# be careful: space between symbols

PROGRAM := EXPRESSION_LIST

EXPRESSION_LIST := EXPRESSION
    | EXPRESSION semicolon EXPRESSION_LIST

EXPRESSION := QUERY_EXPRESSION 
    | UPDATE_EXPRESSION
    | EPSILON

UPDATE_EXPRESSION := PATH assign QUERY_EXPRESSION
    | delete PATH
    | append PATH assign QUERY_EXPRESSION

QUERY_EXPRESSION := ATOM_DATA
    | variableName
    | PATH
    | variableName leftBracket rightBracket
    | variableName leftBracket QUERY_EXPRESSION_LIST rightBracket

QUERY_EXPRESSION_LIST := QUERY_EXPRESSION
    | QUERY_EXPRESSION comma QUERY_EXPRESSION_LIST

PATH := nodeName 
    | nodeName PATH
    | nodeNameVariable
    | nodeNameVariable PATH

ATOM_DATA := true
    | false
    | null
    | string
    | number