dillonkearns / elm-ts-json / TsJson.Codec

A Codec a contain a JSON Decoder a and the corresponding a -> Value encoder.

This module is a port of miniBill/elm-codec. Thank you for the great API design miniBill!

Definition


type alias Codec a =
TsJson.Internal.Codec.Codec a

A value that knows how to encode and decode JSON values.

Running Encoders/Decoders

decoder : Codec a -> TsJson.Decode.Decoder a

Extracts the Decoder contained inside the Codec.

encoder : Codec a -> TsJson.Internal.Encode.Encoder a

Extracts the encoding function contained inside the Codec.

Primitives

string : Codec String

Codec between a JSON string and an Elm String

bool : Codec Basics.Bool

Codec between a JSON boolean and an Elm Bool

int : Codec Basics.Int

Codec between a JSON number and an Elm Int

float : Codec Basics.Float

Codec between a JSON number and an Elm Float

Literals

literal : value -> Json.Encode.Value -> Codec value

stringLiteral : value -> String -> Codec value

Data Structures

maybe : Codec a -> Codec (Maybe a)

Represents an optional value.

list : Codec a -> Codec (List a)

Codec between a JSON array and an Elm List.

array : Codec a -> Codec (Array a)

Codec between a JSON array and an Elm Array.

dict : Codec a -> Codec (Dict String a)

Codec between a JSON object and an Elm Dict.

set : Codec comparable -> Codec (Set comparable)

Codec between a JSON array and an Elm Set.

tuple : Codec a -> Codec b -> Codec ( a, b )

Codec between a JSON array of length 2 and an Elm Tuple.

triple : Codec a -> Codec b -> Codec c -> Codec ( a, b, c )

Codec between a JSON array of length 3 and an Elm triple.

result : Codec error -> Codec value -> Codec (Result error value)

Codec for Result values.

Object Primitives


type ObjectCodec a b

A partially built Codec for an object.

object : b -> ObjectCodec a b

Start creating a Codec for an object. You should pass the main constructor as argument. If you don't have one (for example it's a simple type with no name), you should pass a function that given the field values builds an object.

Example with constructor:

type alias Point =
    { x : Float
    , y : Float
    }

pointCodec : Codec Point
pointCodec =
    Codec.object Point
        |> Codec.field "x" .x Codec.float
        |> Codec.field "y" .y Codec.float
        |> Codec.buildObject

Example without constructor:

pointCodec : Codec { x : Int, y : Bool }
pointCodec =
    Codec.object (\x y -> { x = x, y = y })
        |> Codec.field "x" .x Codec.int
        |> Codec.field "y" .y Codec.bool
        |> Codec.buildObject

field : String -> (a -> f) -> Codec f -> ObjectCodec a (f -> b) -> ObjectCodec a b

Specify the name, getter and Codec for a field.

The name is only used as the field name in the resulting JSON, and has no impact on the Elm side.

maybeField : String -> (a -> Maybe f) -> Codec f -> ObjectCodec a (Maybe f -> b) -> ObjectCodec a b

Specify the name getter and Codec for an optional field.

This is particularly useful for evolving your Codecs.

If the field is not present in the input then it gets decoded to Nothing. If the optional field's value is Nothing then the resulting object will not contain that field.

nullableField : String -> (a -> Maybe f) -> Codec f -> ObjectCodec a (Maybe f -> b) -> ObjectCodec a b

Specify the name getter and Codec for a required field, whose value can be null.

If the field is not present in the input then the decoding fails. If the field's value is Nothing then the resulting object will contain the field with a null value.

This is a shorthand for a field having a codec built using Codec.maybe.

buildObject : ObjectCodec a a -> Codec a

Create a Codec from a fully specified ObjectCodec.

Custom Types

stringUnion : List ( String, value ) -> Codec value

Simple one-to-one mapping of Elm values to TypeScript strings (no arguments, just like values like an enumeration).

import TsJson.Codec exposing (Codec)

type DarkMode
    = Dark
    | Light

darkModeCodec : Codec DarkMode
darkModeCodec =
    Codec.stringUnion [ ( "dark", Dark ), ( "light", Light ) ]

The TsType for darkModeCodec is the following union:

"dark" | "light"


type CustomCodec match v

A partially built Codec for a custom type.

custom : Maybe String -> match -> CustomCodec match value

Starts building a Codec for a custom type.

You need to pass a pattern matching function, built like this:

import TsJson.Codec exposing (Codec)

type Shape
    = Rectangle Int Int
    | Square Int
    | Circle Int

shapeCodec : Codec Shape
shapeCodec =
    Codec.custom (Just "shape")
        (\vRectangle vSquare vCircle shape ->
            case shape of
                Rectangle width height ->
                    vRectangle width height

                Square width ->
                    vSquare width

                Circle radius ->
                    vCircle radius
        )
        |> Codec.namedVariant2 "rectangle" Rectangle ( "width", Codec.int ) ( "height", Codec.int )
        |> Codec.positionalVariant1 "square" Square Codec.int
        |> Codec.namedVariant1 "circle" Circle ( "radius", Codec.int )
        |> Codec.buildCustom

The `TsType` for `shapeCodec` is the following discriminated union:

```typescript
| { shape: "rectangle"; width: number; height: number }
| { shape: "square"; args: [ number ] }
| { shape: "circle"; radius: number }
```

buildCustom : CustomCodec (a -> TsJson.Encode.UnionEncodeValue) a -> Codec a

Build a Codec for a fully specified custom type.

variant0 : String -> v -> CustomCodec (TsJson.Encode.UnionEncodeValue -> c) v -> CustomCodec c v

Define a variant with 0 parameters for a custom type.

Keyword Variants

namedVariant1 : String -> (a -> v) -> ( String, Codec a ) -> CustomCodec ((a -> TsJson.Internal.Encode.UnionEncodeValue) -> c) v -> CustomCodec c v

Define a variant with 1 parameter for a custom type.

namedVariant2 : String -> (a -> b -> v) -> ( String, Codec a ) -> ( String, Codec b ) -> CustomCodec ((a -> b -> TsJson.Encode.UnionEncodeValue) -> c) v -> CustomCodec c v

Define a variant with 2 parameters for a custom type.

namedVariant3 : String -> (a1 -> a2 -> a3 -> v) -> ( String, Codec a1 ) -> ( String, Codec a2 ) -> ( String, Codec a3 ) -> CustomCodec ((a1 -> a2 -> a3 -> TsJson.Encode.UnionEncodeValue) -> c) v -> CustomCodec c v

Define a variant with 3 parameters for a custom type.

namedVariant4 : String -> (a1 -> a2 -> a3 -> a4 -> v) -> ( String, Codec a1 ) -> ( String, Codec a2 ) -> ( String, Codec a3 ) -> ( String, Codec a4 ) -> CustomCodec ((a1 -> a2 -> a3 -> a4 -> TsJson.Encode.UnionEncodeValue) -> c) v -> CustomCodec c v

Define a variant with 4 parameters for a custom type.

namedVariant5 : String -> (a1 -> a2 -> a3 -> a4 -> a5 -> v) -> ( String, Codec a1 ) -> ( String, Codec a2 ) -> ( String, Codec a3 ) -> ( String, Codec a4 ) -> ( String, Codec a5 ) -> CustomCodec ((a1 -> a2 -> a3 -> a4 -> a5 -> TsJson.Encode.UnionEncodeValue) -> c) v -> CustomCodec c v

Define a variant with 5 parameters for a custom type.

namedVariant6 : String -> (a1 -> a2 -> a3 -> a4 -> a5 -> a6 -> v) -> ( String, Codec a1 ) -> ( String, Codec a2 ) -> ( String, Codec a3 ) -> ( String, Codec a4 ) -> ( String, Codec a5 ) -> ( String, Codec a6 ) -> CustomCodec ((a1 -> a2 -> a3 -> a4 -> a5 -> a6 -> TsJson.Encode.UnionEncodeValue) -> c) v -> CustomCodec c v

Define a variant with 6 parameters for a custom type.

namedVariant7 : String -> (a1 -> a2 -> a3 -> a4 -> a5 -> a6 -> a7 -> v) -> ( String, Codec a1 ) -> ( String, Codec a2 ) -> ( String, Codec a3 ) -> ( String, Codec a4 ) -> ( String, Codec a5 ) -> ( String, Codec a6 ) -> ( String, Codec a7 ) -> CustomCodec ((a1 -> a2 -> a3 -> a4 -> a5 -> a6 -> a7 -> TsJson.Encode.UnionEncodeValue) -> c) v -> CustomCodec c v

Define a variant with 7 parameters for a custom type.

namedVariant8 : String -> (a1 -> a2 -> a3 -> a4 -> a5 -> a6 -> a7 -> a8 -> v) -> ( String, Codec a1 ) -> ( String, Codec a2 ) -> ( String, Codec a3 ) -> ( String, Codec a4 ) -> ( String, Codec a5 ) -> ( String, Codec a6 ) -> ( String, Codec a7 ) -> ( String, Codec a8 ) -> CustomCodec ((a1 -> a2 -> a3 -> a4 -> a5 -> a6 -> a7 -> a8 -> TsJson.Encode.UnionEncodeValue) -> c) v -> CustomCodec c v

Define a variant with 8 parameters for a custom type.

Positional Variants

positionalVariant1 : String -> (arg1 -> v) -> Codec arg1 -> CustomCodec ((arg1 -> TsJson.Encode.UnionEncodeValue) -> c) v -> CustomCodec c v

Define a variant with 0 parameters for a custom type.

positionalVariant2 : String -> (arg1 -> arg2 -> v) -> Codec arg1 -> Codec arg2 -> CustomCodec ((arg1 -> arg2 -> TsJson.Encode.UnionEncodeValue) -> c) v -> CustomCodec c v

Define a variant with 2 parameters for a custom type.

positionalVariant3 : String -> (arg1 -> arg2 -> arg3 -> v) -> Codec arg1 -> Codec arg2 -> Codec arg3 -> CustomCodec ((arg1 -> arg2 -> arg3 -> TsJson.Encode.UnionEncodeValue) -> partial) v -> CustomCodec partial v

Define a variant with 3 parameters for a custom type.

positionalVariant4 : String -> (arg1 -> arg2 -> arg3 -> arg4 -> v) -> Codec arg1 -> Codec arg2 -> Codec arg3 -> Codec arg4 -> CustomCodec ((arg1 -> arg2 -> arg3 -> arg4 -> TsJson.Encode.UnionEncodeValue) -> partial) v -> CustomCodec partial v

Define a variant with 3 parameters for a custom type.

positionalVariant5 : String -> (arg1 -> arg2 -> arg3 -> arg4 -> arg5 -> v) -> Codec arg1 -> Codec arg2 -> Codec arg3 -> Codec arg4 -> Codec arg5 -> CustomCodec ((arg1 -> arg2 -> arg3 -> arg4 -> arg5 -> TsJson.Encode.UnionEncodeValue) -> partial) v -> CustomCodec partial v

Define a variant with 3 parameters for a custom type.

positionalVariant6 : String -> (arg1 -> arg2 -> arg3 -> arg4 -> arg5 -> arg6 -> v) -> Codec arg1 -> Codec arg2 -> Codec arg3 -> Codec arg4 -> Codec arg5 -> Codec arg6 -> CustomCodec ((arg1 -> arg2 -> arg3 -> arg4 -> arg5 -> arg6 -> TsJson.Encode.UnionEncodeValue) -> partial) v -> CustomCodec partial v

Define a variant with 3 parameters for a custom type.

positionalVariant7 : String -> (arg1 -> arg2 -> arg3 -> arg4 -> arg5 -> arg6 -> arg7 -> v) -> Codec arg1 -> Codec arg2 -> Codec arg3 -> Codec arg4 -> Codec arg5 -> Codec arg6 -> Codec arg7 -> CustomCodec ((arg1 -> arg2 -> arg3 -> arg4 -> arg5 -> arg6 -> arg7 -> TsJson.Encode.UnionEncodeValue) -> partial) v -> CustomCodec partial v

Define a variant with 3 parameters for a custom type.

positionalVariant8 : String -> (arg1 -> arg2 -> arg3 -> arg4 -> arg5 -> arg6 -> arg7 -> arg8 -> v) -> Codec arg1 -> Codec arg2 -> Codec arg3 -> Codec arg4 -> Codec arg5 -> Codec arg6 -> Codec arg7 -> Codec arg8 -> CustomCodec ((arg1 -> arg2 -> arg3 -> arg4 -> arg5 -> arg6 -> arg7 -> arg8 -> TsJson.Encode.UnionEncodeValue) -> partial) v -> CustomCodec partial v

Define a variant with 3 parameters for a custom type.

Inconsistent structure

oneOf : Codec a -> List (Codec a) -> Codec a

Try a set of decoders (in order). The first argument is used for encoding and decoding, the list of other codecs is used as a fallback while decoding.

This is particularly useful for backwards compatibility. You would pass the current codec as the first argument, and the old ones (eventually mapped) as a fallback list to use while decoding.

Mapping

map : (a -> b) -> (b -> a) -> Codec a -> Codec b

Transform a Codec.

Fancy Codecs

succeed : a -> Codec a

Create a Codec that produces null as JSON and always decodes as the same value.

recursive : (Codec a -> Codec a) -> Codec a

Create a Codec for a recursive data structure. The argument to the function you need to pass is the fully formed Codec.

fail : String -> Codec a

Ignore the JSON and make the decoder fail. This is handy when used with oneOf where you want to give a custom error message in some case. The encoder will produce null.

lazy : (() -> Codec a) -> Codec a

This is useful for recursive structures that are not easily modeled with recursive. Have a look at the Json.Decode docs for examples.

value : Codec Json.Decode.Value

Create a Codec that doesn't transform the JSON value, just brings it to and from Elm as a Value.

build : TsJson.Internal.Encode.Encoder a -> TsJson.Decode.Decoder a -> Codec a

Build your own custom Codec. Useful if you have pre-existing Decoders you need to use.

tsType : Codec value -> Internal.TsJsonType.TsType