Adds an example to README

Author: dragonwasrobot

README.md

@@ -9,7 +9,8 @@ This project requires that you already have [elixir](http://elixir-lang.org/)
 and its build tool `mix` installed, this can be done with `brew install elixir`
 or similar.
 
-- Clone this repository: `git clone [email protected]:dragonwasrobot/json-schema-to-elm.git`
+- Clone this repository: `git clone
+  [email protected]:dragonwasrobot/json-schema-to-elm.git`
 - Build an executable: `MIX_ENV=prod mix build`
 - An executable, `js2e`, has now been created in your current working directory.
 
@@ -22,3 +23,159 @@ works is still in progress, but feel free to take a look at the `examples`
 folder which contains an example of a pair of JSON schemas and their
 corresponding Elm output. Likewise, representations of each of the different
 JSON schema types are described in the `lib/types` folder.
+
+## Example
+
+If we supply `js2e` with the following JSON schema file, `definitions.json`:
+``` json
+{
+    "$schema": "http://json-schema.org/draft-04/schema",
+    "title": "Definitions",
+    "id": "http://example.com/definitions.json",
+    "description": "Schema for common types",
+    "definitions": {
+        "color": {
+            "id": "#color",
+            "type": "string",
+            "enum": [ "red", "yellow", "green", "blue" ]
+        },
+        "point": {
+            "id": "#point",
+            "type": "object",
+            "properties": {
+                "x": {
+                    "type": "number"
+                },
+                "y": {
+                    "type": "number"
+                }
+            },
+            "required": [ "x", "y" ]
+        }
+    }
+}
+```
+
+it produces the following Elm file, `Domain/Definitions.elm`:
+
+``` elm
+module Domain.Definitions exposing (..)
+
+-- Schema for common types
+
+import Json.Decode as Decode
+    exposing
+        ( float
+        , int
+        , string
+        , list
+        , succeed
+        , fail
+        , map
+        , maybe
+        , field
+        , at
+        , andThen
+        , oneOf
+        , nullable
+        , Decoder
+        )
+import Json.Decode.Pipeline
+    exposing
+        ( decode
+        , required
+        , optional
+        , custom
+        )
+import Json.Encode as Encode
+    exposing
+        ( Value
+        , float
+        , int
+        , string
+        , list
+        , object
+        )
+
+
+type Color
+    = Red
+    | Yellow
+    | Green
+    | Blue
+
+
+type alias Point =
+    { x : Float
+    , y : Float
+    }
+
+
+colorDecoder : String -> Decoder Color
+colorDecoder color =
+    case color of
+        "red" ->
+            succeed Red
+
+        "yellow" ->
+            succeed Yellow
+
+        "green" ->
+            succeed Green
+
+        "blue" ->
+            succeed Blue
+
+        _ ->
+            fail <| "Unknown color type: " ++ color
+
+
+pointDecoder : Decoder Point
+pointDecoder =
+    decode Point
+        |> required "x" Decode.float
+        |> required "y" Decode.float
+
+
+encodeColor : Color -> Value
+encodeColor color =
+    case color of
+        Red ->
+            Encode.string "red"
+
+        Yellow ->
+            Encode.string "yellow"
+
+        Green ->
+            Encode.string "green"
+
+        Blue ->
+            Encode.string "blue"
+
+
+encodePoint : Point -> Value
+encodePoint point =
+    let
+        x =
+            [ ( "x", Encode.float point.x ) ]
+
+        y =
+            [ ( "y", Encode.float point.y ) ]
+    in
+        object <|
+            x
+                ++ y
+```
+
+which contains an Elm type for the `color` and `point` definitions along with
+their corresponding JSON decoders and encoders.
+
+Furthermore, if we supply `js2e` with another JSON schema file that references
+any of the definitions in `definitions.json`, e.g.
+
+``` json
+{ "$ref" : "http://example.com/definitions.json#point" }
+```
+
+then the corresponding Elm file output will import the definitions `Point`,
+`pointDecoder` and `encodePoint` from `Domain.Definitions`.