JSONM

#JSON with macros (JSONM)

JSONM is a JSON extension that allows using macro definitions inside JSON files.

###Why? The main goals of this format are to make configuration files more readable and to get rid of scripts that generate huge configuration files.

###What? JSONM is superset of JSON. Any JSON object may be treated as JSON with macros. JSON with macros is also a valid JSON object – the difference lies in enhancing some JSON properties to allow reuse of similar parts of large JSON objects.

###How? Using a simple preprocessor, we generate standard JSON objects from user-friendly JSONM by processing all macros and substituting all constants. .

###Syntax JSONM is a JSON object with two special optional keys: consts and macros:

  {
    "consts": [
      constDefinition,
      constDefinition,
      …
    },
    "macros": {
      "macroName1": macroDefinition,
      "macroName2": macroDefinition,
      …
    },
    "customProperty1": valueWithMacros,
    "customProperty2": valueWithMacros
  }

• value
  any JSON value (string, object, number, etc.)
• valueWithMacros
  JSON value that may contain macroCall, paramSubstitution, builtInCall
• macroCall
"@macroName(param1,param2,…)"
  or

 {
   "type": "macroName",
   "paramName1": valueWithMacros,
   "paramName2": valueWithMacros,
   …
 }

• paramSubstitution string of form %paramName%. Examples: "%paramName%", "a%paramName%b". %paramName% will be replaced with value of the corresponding parameter. If the whole string is a parameter substitution (i.e., "%paramName%") parameter values may be any valueWithParams. Otherwise, it should be a string.
• builtInCall Basically the same as template call, but has no short form.

 {
   "type": "if|transform|process",
   … params for this call …
 }

###Comments JSONM allows C-style comments, which are removed by the preprocessor. Example:

 {
   // some comment here
   "key": /* and one more comment here */ "value/**/"
 }

After preprocessing:

 {
   "key": "value/**/"
 }

###Macro Macro is a reusable piece of JSON. One can think about it as a function that takes an arbitrary list of values and returns valueWithMacros.

####Macro definition The "macros" property should be an object with macro definitions. Syntax is following:

 {
   "macros": {
     "macroName": {
       "type": "macroDef",
       "params": macroDefParamList,
       "result": valueWithMacros
     }
   }
 }

"result" is JSONM that may contain paramSubstitution.

• macroDefParamList [ macroDefParam, macroDefParam, …]
• macroDefParam "paramName" | { "name": "paramName", "default": value }

Example:

 {
   "pair": {
     "type": "macroDef",
     "params": [ "key", "value" ],
     "result": {
       "%key%": "%value%"
     }
   },
   "fullName": {
     "type": "macroDef",
     "params": [ "first", "last" ],
     "result": [ "@pair(first,%first%)", "@pair(last,%last%)" ]
   }
 }

Parameters may have defaults. Example:

 {
   "car": {
     "type": "macroDef",
     "params": [
       "model",
       // parameter with default
       {
         "name": "color",
         "default": "green"
       }
     ],
     "result": {
       "model": "%model%",
       "color": "%color%"
     }
   }
 }

####Macro call Given an object with the macros from our previous examples, other properties may include macro calls:

 {
   "person": "@fullName(John,Doe)",
   "car": "@car(Mercedes)"
 }

After preprocessing:

 {
   "person": {
     "first": "John",
     "last": "Doe"
   },
   "car": {
     "model": "Mercedes",
     "color": "green"
   }
 }

###Consts Consts are valueWithMacros that may be substituted everywhere. One may use only built-in macros and built-in calls in consts.

 {
   "consts": [
     {
       "type": "constDef",
       "name": "author",
       "value": "John Doe"
     },
     {
       "type": "constDef",
       "name": "copyright",
       "value": "%author% owns it"
     }
   ],
   "file": "%copyright%. Some content"
 }

After preprocessing:

 {
   "file": "John Doe owns it. Some content"
 }

###Escaping These characters have special meaning for the preprocessor: ‘@', ‘%', ‘(', ‘)', ‘,'. Add two backslashes (\) before any character to escape the character. It will then be added to the string 'as is' and will not be interpreted as a preprocessor instruction. To escape a backslash, write \\. Two backslashes are required because JSON uses a single backslash () as an escape character. Example:

 {
   "email": "fake\\@fake.fake",
   "valid": "100\\%",
   "backslash": "\\\\"
 }

After preprocessing:

 {
   "email": "fake@fake.fake",
   "valid": "100%",
   "backslash": "\\"
 }

Note: "backslash" is JSON property, so it will be interpreted as only one backslash.

###Built-in macros These macros perform different operations on JSON values.

####import Usage: @import(path)
Allows loading JSONM from external source. Example:

File: cities.json

 {
   "cities": [
     "New York",
     "Washington"
   ]
 }

File: city.json

 {
   "city": {
     "type": "select",
     "key": 0,
     "dictionary": "@import(cities.json) "
   }
 }

After preprocessing, city.json becomes:

 {
   "city": "New York"
 }

####int, str, bool Usage: @int(5); @str(@int(5)); @bool(true)
@int casts its argument to an integer:

 {
   "key": "@int(100)"
 }

After preprocessing:

 {
   "key": 100
 }

@str casts its argument to string; @bool to boolean.

####keys, values Usage: @keys(object); @values(object)
@keys returns list of object keys; @values returns list of object values:

 {
   "type": "keys",
   "dictionary": {"a": 1, "b": 2}
 }

After preprocessing:

 ["a", "b"]

####merge Usage:

 "type": "merge",
 "params": [ list1, list2, list3, ... ]

or

 "type": "merge",
 "params": [ obj1, obj2, obj3, ... ]

or

 "type": "merge"
 "params": [ str1, str2, str3, ... ]

Combines multiple lists or objects into one. In case params is a list of strings, merge concatenates them.

 {
   "type": "merge",
   "params": [
     [1, 2],
     [3, 4]
   ]
 }

After preprocessing:

 [1, 2, 3, 4]

If params is a list of objects, it will also be merged :

 {
   "type": "merge",
   "params": [
     {"a": 1, "b": 2},
     {"b": 3, "c": 4}
   ]
 }

After preprocessing:

 {
   "a": 1,
   "b": 3,
   "c": 4
 }

####select Usage: @select(obj,string) or @select(list,int)
Returns element from list or object.

 {
   "type": "select",
   "key": "a",
   "dictionary": {
     "a": 1,
     "b": 2
   }
 }

After preprocessing:

 1

####shuffle Usage: @shuffle(list)
Randomly shuffles a list.

 {
   "type": "shuffle",
   "dictionary": [1, 2, 3, 4]
 }

After preprocessing, (one possible example):

 [2, 4, 3, 1]

####slice Usage:

 "type": "slice",
 "dictionary": obj,
 "from": string,
 "to": string

or

 "type": "slice",
 "dictionary": list/string,
 "from": int,
 "to": int

Returns a slice (subrange) of list, object or string.

 {
   "type": "slice",
   "from": 1,
   "to": 2,
   "dictionary": [1, 2, 3, 4]
 }

After preprocessing:

 [2, 3]

####range Usage: @range(@int(1),@int(2))
Returns list of integers [from, from + 1, ..., to]

 {
   "myRange": "@range(@int(1),@int(2))"
 }

After preprocessing:

 {
   "myRange": [1, 2]
 }

####isArray, isBool, isInt, isObject, isString Usage: @isArray(value); isBool(value); etc.
Return true if value is list, bool, int, object or string respectively:

 "@isString(abc)"

After preprocessing:

 true

####add, sub, mul, div, mod Usage: @add(A,B); @sub(A,B); etc.
Perform corresponding operation on integers:

 // 2*3 + 5
 { "value": "@add(@mul(@int(2),@int(3)),@int(5))" }

After preprocessing:

 "value": 11

####contains Usage: @contains(dictionary,value)
Returns true if dictionary contains a key; list contains a value; string contains a substring:

 { "condition": "@contains(abacaba,aca)" }

After preprocessing:

 { "condition": true }

####empty Usage: @empty(dictionary)
Returns true if object, array or string is empty.

####less Returns true if A is less than B. Can compare any values except objects.

 { "condition": "@less(bcd,abcd)" }

After preprocessing:

 { "condition": false }

####equals Usage: @equals(A,B)
Returns true if A == B. Can compare any values.

####and, or Returns true if A and B; A or B respectively. Both A and B should be booleans.

###Built-in calls ####if Usage:

 "type": "if",
 "condition": bool,
 "is_true": any value
 "is_false": any value

Conditional operator: returns is_true property if condition is true, is_false otherwise:

 {
   "value": {
     "type": "if",
     "condition": "@equals(a,a)"
     "is_false": "Oops",
     "is_true": "Yeah"
   }
 }

After preprocessing:

  { "value": "Yeah" }

####transform Usage:

 "type": "transform",
 "dictionary": obj,
 "itemTransform": macro with extended context
 "keyTranform": macro with extended context (optional)
 "itemName": string (optional, default: item)
 "keyName": string (optional, default: key)

or

 "type": "transform",
 "dictionary": list,
 "itemTranform": macro with extended context
 "keyName": string (optional, default: key)
 "itemName": string (optional, default: item)

Transforms elements of a list or object, using itemTransform and keyTransform properties. keyTransform is optional; available only if the dictionary is an object. itemTransform and keyTransform are valueWithMacros and may use two additional parameters: key and item (parameter names are configured with keyName and itemName properties).

 {
   "type": "transform",
   "keyTransform": "%item%",
   "itemTransform": "%key%",
   "dictionary": {
     "a": "b",
     "b": "c"
   }
 }

After preprocessing:

 {
   "b": "a",
   "c": "b"
 }

####process Usage:

 "type": "process",
 "initialValue": any value,
 "transform": macro with extended context
 "keyName": string (optional, default: key)
 "itemName": string (optional, default: item)
 "valueName": string (optional, default: value)

Iterates over an object or array and transforms "value". Literally:

  value = initialValue
  for each (key, item) in dictionary:
    value = transform(key, item, value)
  }
  return value

transform is valueWithMacros and may use three additional parameters: key, item and value (parameter names are configured with keyName, itemName and valueName properties).

 {
   "type": "process",
   "initialValue": "",
   "dictionary": ["a", "b", "c", "d"],
   "transform": "%item%%value%"
 }

After preprocessing:

 "dcba"