A Json Object is reified as a Racket hashmap, Json array to a Racket list and Strings, Booleans and Numbers mapped to Racket’s types. A special symbol is reserved to indicating a Json null value.

A parsed Json graph follows the naive recursive data structure definition as Json is a string, number, boolean (true or false), list of Json or an object with a multiplicity of unique symbol labeled Json.

(require tjson ) package: tjson

2Json Parsed Data Structure🔗 i

value
Json :
(Rec (U String Boolean JsNullNumber (Listof Json)
(HashTable Symbol Json)))

A translation of a parsed Json data structure reflectiing it recursive nature.

value
JsObject:(HashTable Symbol Json)

A define-type alias reflecting a Json Object as a hashmap of symbols and Json values.

value
JsList:(Listof Json)

A define-type alias reflecting a Json Array as a Racket List of Json.

value
JsNull:'JsNull

A Json null value is reflected in Racket as a special reserved symbol. JsNull is a define-type alias for the symbol value at the type level. In Typed Racket each symbol is given a unique type containing only that symbol.

While the type Symbol has all symbols as inhabiting values, the type ’JsNull has only the single inhabiting value ’JsNull.

3Json Parsing🔗 i

procedure
(string->jsonjson)→Json
json:String

Parse a string representation of Json into a Typed Racket Json structure.

Examples:

> (string->json"42")

- : Json

42
> (string->json"\"Mary had a little lamb\"")

- : Json

"Mary had a little lamb"
> (string->json"[\"lamb\", \"cat\", \"dog\"]")

- : Json

'("lamb""cat""dog")
> (string->json"{\"cat\" : \"meow\", \"dog\" : \"bark\", \"lamb\" : \"bleet\"}")

- : Json

'#hasheq((dog. "bark")(cat. "meow")(lamb. "bleet"))

4Json Construction🔗 i

procedure
(jsobjectattributes)→JsObject
attributes:(Listof (Pair Symbol Json))

Creates a JsObject instance from a list of symbol and json value associations. Note as a JsObject is just a transparent type alias for a HashMap any of the standard Racket hashmap construction procedures maybe used as well such as (hash ...) or (make-hash ...).

Example:

> (jsobject'((cat. "meow")(dog. "bark")(lamb. "bleet")(turtle. JsNull)))

- : JsObject

'#hasheq((dog. "bark")(turtle. JsNull)(cat. "meow")(lamb. "bleet"))

5JsObject🔗 i

5.1JsObject Attribute Lookup🔗 i

Lookup an JsObject attribute’s (key) json value.

procedure
(jsattribute?jobjkey)→Boolean
jobj:JsObject
key:Symbol

Whether the attribute exists for the jsobject.

procedure
(jsattributejobjkey)→(Option Json)
jobj:JsObject
key:Symbol

Returns the value of the given attribute key if it exists otherwise #f.

Note: For boolean values attributes, given how Option values are implementinted in Typed Racket, the #f return value cannot be used to descriminate between an existing attribute whose value is #f or a missing attribute.

procedure
(jsattribute-orelsejobjkeydefault)→Json
jobj:JsObject
key:Symbol
default:(-> Json)

Returns the json value of the attribute key if it exists otherwise the json returned by the provided thunk.

5.2JsObject Modification🔗 i

By design JsObjects are currently implemented as mutable hashmaps and may be mutated. Recall that a JsObject is a type alias for a Racket mutable hashmap. For details concerning concurrent modification see the Racket documantation for hashmaps.

The Racket implemetation of hashmap operations is rich and only a subset are currently wrapped in this library. Additional capabilities such as union, jsobject-union! will added at a later time.

procedure
(jsobject-add!jobjkeyjson)→Void
jobj:JsObject
key:Symbol
json:Json

Adds the attribute to a JsObject overwriting an existing attribute.

procedure
(jsobject-remove!jobjkey)→Void
jobj:JsObject
key:Symbol

Removes the attribute from the jsobject if it exists. It is not an error to attempt to remove a non-existing attribute.

procedure
(jsobject-update!jobjkeyupdater)→Void
jobj:JsObject
key:Symbol
updater:(-> JsonJson)

Modifies an existing attribute value. A fail:contract exception is thrown if the attribute does not exist.

Examples:

> (define j(jsobject'((cat. "meow"))))
> (jsobject-update!j'cat(λ (says)(string-append (cast saysString )" purr")))
> j

- : JsObject

'#hasheq((cat. "meow purr"))

6Json Emission🔗 i

procedure
(json->stringjson)→String
json:Json

Emit a string representation of a Json data structure.

Example:

> (json->string(jsobject'((cat. "meow")(dog. "bark")(lamb. "bleet")(turtle. JsNull))))

- : String

"{\"turtle\": null, \"cat\": \"meow\", \"lamb\": \"bleet\", \"dog\": \"bark\"}"

7Port Serialization🔗 i

procedure
(write-jsonjsonoutp)→Void
json:Json
outp:Output-Port

Serialize a Json data structure out the provided port as a json string.

procedure
(read-jsoninp)→Json
inp:Input-Port

Read a json value from the input port.

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