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Mark edited this page Mar 25, 2017 · 18 revisions

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 a special optional key macros:

  {
    "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)"
 }

Trailing and leading spaces are trimmed from arguments. 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.

 {
   "macros": {
     "author": {
       "type": "constDef",
       "result": "John Doe"
     },
     "copyright": {
       "type": "constDef",
       "result": "%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": "[email protected]",
   "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]

size

Usage:

  "type": "size",
  "dictionary": list/string/object

Returns size of object/array/string.

 {
   "type": "size",
   "dictionary": [1, 2],
 }

After preprocessing:

 2

sort

Usage:

 "type": "sort",
 "dictionary": list,

Sort a list of strings/numbers.

 {
   "type": "sort",
   "dictionary": [2, 1],
 }

After preprocessing:

 [1, 2]

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"

foreach

Usage:

 "type": "foreach",
 "key": string (optional, default: key)
 "item": string (optional, default: item)
 "from": object or list
 "where": macro with extended context (optional, %key% and %item%)
 "use": macro with extended context (optional, %key% and %item%)
 "top": int (optional)
 "noMatchResult": any value (optional)

foreach (key, item) from where use top for top items from dictionary "from" which satisfy "where" condition merge expansions into one dictionary.

For example, to filter dictionary:

{
 "type": "foreach",
 "from": <dictionary>,
 "where": <condition>
}

To convert object to list:

{
 "type": "foreach",
 "from": <object>,
 "use": [ <list item> ]
 "noMatchResult": []
}

To grab at most 2 items from that satisfy :

{
 "type": "foreach",
 "from": <dictionary>
 "where": <condition>
 "top": 2
}

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