Language for JSON (JavaScript Object Notation)

Made for the purposes of HY-352 Software Engineering course, in Computer Science Department, University of Crete.

In this project, a specific-purpose language is implemented for definitions and usage of data in JSON format. This language is compiled to C++ by including only the "JSONlang.h" header file.

Language Format:

#include "JSONlang.h"
json variable definition1
json variable definition2
…
PROGRAM_BEGIN
    json variable definition3
    …
    json editing statement1
    json variable definitionk
    …
    json editing statement2 
    … 
    json editing statementn 
PROGRAM_END

NOTE: No semicolon is used.

Language elements

1. Definition of JSON variable

JSON(name) = value

Where name is the id of the defined variable.
Value can be a string, number, object, array, true, false, null

Value Type	Example	Syntax
string	"example"	STRING("example")
number	34	NUMBER(34)
true	true	TRUE
false	false	FALSE
null	null	NULL
object	{  "title" : "C++14",  "year" : 2014 }	OBJECT {  KEY(title) : STRING("C++14"),  KEY(year) : NUMBER(2014) }
array	[ ] // Empty Array [  2020,  "CoViD",  {   "country" : "Greece",   "deaths" : 5598  } ]	ARRAY // Empty Array ARRAY [  NUMBER(2020),  STRING("CoViD"),  OBJECT {   KEY(country) : STRING("Greece"),   KEY(deaths) : NUMBER(5598)  } ]

Examples

//define emptyObj json with empty object
JSON(emptyObj) = OBJECT {}

//define emptyArray json with empty array
JSON(emptyArray) = ARRAY

//define book json with an object containing data for a book
JSON(book) = OBJECT {
    KEY(title) : STRING("Gone Girl"),
    KEY(published) : NUMBER(2012),
    KEY(type) : STRING("Thriller"),
    KEY(author) : OBJECT {
        KEY(firstname) : STRING("GILLIAN"),
        KEY(surname) : STRING("FLYNN"),
        KEY(age) : NUMBER(45)
    }
}

//define week_temperatures json with an array of numbers
JSON(week_temperatures) = ARRAY [
    NUMBER(20), NUMBER(19.5), NUMBER(19), NUMBER(20),
    NUMBER(19), NUMBER(18.5), NUMBER(19)
]

//define students json with an array of objects representing students
JSON(students) = ARRAY [
    OBJECT {
        KEY(name) : STRING("Kevin Malone"),
        KEY(id) : NUMBER(4444),
        KEY(grades) : ARRAY [
            OBJECT { KEY(cs100) : NUMBER(9.5) },
            OBJECT { KEY(cs150) : NUMBER(9) },
            ...
        ]
    },
    ...
]

2. Editing of JSON variables and values

SET json_value ASSIGN value 

Sets a value to an existing JSON variable.
The value must be of the same type of the defined variable, except if value is contained in an ARRAY or an OBJECT.

Examples

//change 3rd day temperature from 19 to 22
SET week_temperatures[2] ASSIGN NUMBER(22)

//change 3rd day temperature from 19 to "Unknown"
SET week_temperatures[2] ASSIGN STRING("Unknown")

//email field does not existin students[0], so it adds it
SET students[0]["email"] ASSIGN STRING("kevin_m@hotmail.com")

//assign new object in emptyObj json
SET emptyObj ASSIGN OBJECT{ KEY(a) : STRING("alpha") }

SET json_array APPEND value1, value2, …

Adds the values of the given arguments (value1, value2, ...) to the JSON value, which must be an ARRAY.

Examples

//appends values 23, 22, 20 to the end of the temperature array
SET week_temperatures APPEND NUMBER(23), NUMBER(22), NUMBER(20)

//appends a grade for course cs255
SET students[0]["grades"] APPEND OBJECT { KEY(cs255) : NUMBER(9) }

ERASE json_value_or_variable

Deletes inner values of JSON objects or arrays, in which they are contained. In case of JSON variable (which must be an object or an array), it just erases all its elements and becomes empty ({ } or [ ])

ERASE book["author"]["age"] //removes age from author object of book
ERASE book["type"] //removes type of book
ERASE book //removes all book data, now book is an empty object

3. Operators

Usage of JSON values as expressions with arithmetic, logical, relational and equality operators support.

• Arithmetic (+, -, *, /, %) and logical (>, >=, <, <=) operators can be used only between NUMBER values.
• Special case of plus (+) operator, which can be used also between strings, arrays or objects.
• Logical (&&, ||, !) operators can be used only between BOOLEAN values.
• Equality operators can be used only between values of the same type.

Examples

JSON(cs352_ang) = OBJECT { KEY(exam) : NUMBER(7), KEY(project) : NUMBER(8) }
JSON(students) = ARRAY [
    OBJECT {
        KEY(name) : STRING("Angela ") + STRING("Martin"),
        KEY(id) : NUMBER(4444),
        KEY(grades) : ARRAY [
            OBJECT {
                KEY(hy352) : cs352_ang["exam"] * NUMBER(0.75) + cs352_ang["project"] * NUMBER(0.25)
            }
        ]
    }
]

4. Special Functions

SIZE_OF(json_value_or_variable)

Returns the number of the elements in an array or an object (for other values, it returns 1)

IS_EMPTY(json_value_or_variable)

Checks if an array or an object is empty (for other values, it returns false)

HAS_KEY(json_value_or_variable, key)

Checks if key exists in an object (for other values, it returns false)

TYPE_OF(json_value_or_variable)

Returns the type of the argument as string ("string", "number", "boolean", "object", "array", "null")

5. Print of JSON variables and values

PRINT json_expression1, json_expression2, …

Examples

PRINT book["title"]             //prints:Gone Girl
PRINT book["author"]            //prints: {firstname:”Gillian”,surname:“Flynn”,age:45}
PRINT book                      //prints: the whole json for book
PRINT HAS_KEY(book, "author")   //prints: true                                
PRINT STRING("Book has key author? "), HAS_KEY(book, "author") //prints: Book has key author? True