JSON

This package provides data types, a parser and pretty printer, and conversion operations for JSON.

Representing JSON values in Curry

A JSON value can be a primitive, i.e. true, false, null, a string or a number, an array of JSON values or an object mapping strings to JSON values. In Curry, a JSON value is represented by the data type JValue from the JSON.Data module:

data JValue = JBool Bool
            | JNull
            | JString String
            | JInt Int
            | JNumber Float
            | JArray [JValue]
            | JObject JObject

JObject is an abstract type representing a mapping from names (strings) to JSON values (see module JSON.Data for operations in this type).

In contrast to raw JSON, this definition distinguishes between integers and other numbers. Actually, the JSON parser (see below) returns a number as a JInt if its textual representation does not contain a decimal point and an exponent.

Parsing JSON strings

parseJSON from JSON.Parser can be used to parse a JSON string into a JValue:

> parseJSON "{ \"hello\": [\"world\", \"kiel\"] }"
Just (JObject [("hello", JArray [JString "world", JString "kiel"])])

Printing JSON strings

ppJSON from JSON.Pretty will turn a JValue into a pretty printed string. If you want more control over the layout of the resulting string, you can use ppJValue from the same value to obtain a Doc for Curry’s Pretty module from a JValue.

Converting to and from JSON

The module JSON.Convert defines a defines a type class ConvertJSON and various instances for standard types to convert Curry values to JSON values and vice versa. As apparent from these instance definitions, it is quite easy to define instances for other user-defined data types.