elm/libraries/Json.elm

-- TOOD: Evan please review texts

module Json where

import Dict as Dict
import JavaScript as JS
import Native.Json as Native

-- This datatype can represent all valid values that can be held in a JSON
-- object. In Elm, a proper JSON object is represented as a (Dict String JsonValue)
-- which is a mapping from strings to Json Values.
data JsonValue
    = String String
    | Number Float
    | Boolean Bool
    | Null
    | Array [JsonValue]
    | Object (Dict String JsonValue)


-- String Converters

-- Convert a `JsonValue` into a prettified string.
-- The first argument is a separator token (e.g. \" \", \"\\n\", etc.) that will
-- be used for indentation in the prettified string version of the JSON.
toString : String -> JsonValue -> String
toString sep v = JS.toString (Native.toJSString sep v)

-- Convert a proper JSON object into a JavaScript string.
-- Note that the type JSString seen here is not the same as the type constructor
-- JsonString used elsewhere in this module.
toJSString : String -> JsonValue -> JSString

-- Parse a string representation of a proper JSON object into
-- its Elm representation.
fromString : String -> Maybe JsonValue
fromString s = Native.fromJSString (JS.fromString s)

-- Parse a JavaScript string representation of a proper JSON object into
-- its Elm representation.
fromJSString : JSString -> Maybe JsonValue

-- Convert a JS object into a `JsonValue`.
fromJSObject : JSObject -> JsonValue

-- Convert a `JsonValue` into a `JSObject`. Paired with the
-- [`JavaScript.Experimental` library](/docs/JavaScript/Experimental.elm),
-- This lets you convert strings into Elm records:
--
--       import JavaScript.Experimental as JS
--
--       stringToRecord str =
--           case fromString str of
--             Just jsonValue -> Just (JS.toRecord (toJSObject jsonValue))
--             Nothing -> Nothing
toJSObject : JsonValue -> JSObject

 {-- Extract Elm values from Json values

 string : JsonValue -> String
 string v = case v of { String s -> s ; _ -> "" }

 number : JsonValue -> Float
 number v = case v of { Number n -> n ; _ -> 0 }

 boolean : JsonValue -> Bool
 boolean v = case v of { Boolean b -> b ; _ -> False }

 array : JsonValue -> [JsonValue]
 array v = case v of { Array a -> a ; _ -> [] }

 object : JsonValue -> Dict String JsonValue
 object v = case v of { Object o -> o ; _ -> Dict.empty }


 -- Extract Elm values from dictionaries of Json values

 -- Find a value in a Json Object using the passed get function. If the key is
 -- not found, this returns the given default/base value.
 find get base =
   let f key dict =
           case Dict.lookup key dict of
             Nothing -> base
             Just v  -> get v
   in  f

 -- Find a string value in an Elm Json object. If the key is not found or the
 -- value found is not a string, this returns the empty string.
 findString : String -> Object -> String
 findString = find string ""

 -- Find a number value in an Elm Json object. If the key is not found or the
 -- value found is not a number, this returns 0
 findNumber : String -> Object -> Float
 findNumber = find number 0

 -- Find a boolean value in an Elm Json object. If the key is not found or the
 -- value found is not a boolean, this returns the False.
 findBoolean : String -> Object -> Bool
 findBoolean = find boolean False

 -- Find an array value in an Elm Json object. If the key is not found or the
 -- value found is not an array, this returns an empty list.
 findArray : String -> Object -> [JsonValue]
 findArray = find array []

 -- Find an object value in an Elm Json object. If the key is not found or the
 -- value found is not an object, this returns an empty object.
 findObject : String -> Object -> Object
 findObject = find object Dict.empty
 --}