Json Module

JSON parsing and encoding.

The Json module provides functions for converting between JSON strings and Keel values. JSON objects map to records, arrays to lists, strings/numbers/booleans to their Keel equivalents, and null to Unit.

Common patterns

import Json

-- Parse JSON (type annotation required for generic parse)
let data: Result { name: String, age: Int } String = Json.parse "{\"name\": \"Bob\", \"age\": 30}"

-- Type-specific parsers don't need annotations
let n = Json.parseInt "42"

-- Encode Keel values to JSON
let jsonStr = Json.encode { x = 1, y = 2 }

-- Extract a field from JSON
let name = Json.get "name" "{\"name\": \"Bob\"}"

Type mapping

JSON	Keel
object	Record
array	List
string	String
number (int)	Int
number (float)	Float
boolean	Bool
null	Unit

Functions

Parsing

`Json.parse`

String -> Result a String

Parse a JSON string into a Keel value. Objects become records, arrays become lists. Requires a type annotation on the result because the return type is generic.

Example:

import Json
let result: Result { name: String } String = Json.parse "{\"name\": \"Bob\"}"

Try it

Notes: A type annotation is required (e.g., let x: Result MyType String = Json.parse ...). JSON null maps to Unit, numbers to Int or Float. Use parseInt, parseString, etc. when you know the expected type.

See also: Json.encode, Json.parseInt, Json.parseString

`Json.parseString`

String -> Result String String

Parse a JSON string and return only the string value.

Example:

import Json

Json.parseString "\"hello\""

-- Ok "hello"

Try it

Notes: Returns Err if the JSON value is not a string.

See also: Json.parse, Json.parseInt

`Json.parseInt`

String -> Result Int String

Parse a JSON string and return only the integer value.

Example:

import Json

Json.parseInt "42"

-- Ok 42

Try it

Notes: Returns Err if the JSON value is not an integer.

See also: Json.parse, Json.parseFloat

`Json.parseFloat`

String -> Result Float String

Parse a JSON string and return only the float value.

Example:

import Json

Json.parseFloat "3.14"

-- Ok 3.14

Try it

Notes: Returns Err if the JSON value is not a number.

See also: Json.parse, Json.parseInt

`Json.parseBool`

String -> Result Bool String

Parse a JSON string and return only the boolean value.

Example:

import Json

Json.parseBool "true"

-- Ok True

Try it

Notes: Returns Err if the JSON value is not a boolean.

See also: Json.parse

Encoding

`Json.encode`

a -> String

Encode a Keel value as a compact JSON string.

Example:

import Json

Json.encode { name = "Alice" }

-- "{\"name\":\"Alice\"}"

Try it

Notes: Records become objects, lists become arrays.

See also: Json.encodePretty, Json.parse

`Json.encodePretty`

Int -> a -> String

Encode a Keel value as pretty-printed JSON with the given indentation.

Example:

import Json

Json.encodePretty 2
{ x = 1 }

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Notes: The Int argument specifies the number of spaces per indent level.

See also: Json.encode

Access

`Json.get`

String -> String -> Result String String

Get a field value from a JSON string as a JSON string.

Example:

import Json
Json.get "name" "{\"name\":\"Bob\"}"  -- Ok "\"Bob\""

Try it

Notes: Returns the field value as a JSON-encoded string.

See also: Json.parse