Add part4

advanced/part4/src/Article/Slug.elm

@@ -0,0 +1,35 @@
+module Article.Slug exposing (Slug, decoder, toString, urlParser)
+
+import Json.Decode as Decode exposing (Decoder)
+import Url.Parser exposing (Parser)
+
+
+
+-- TYPES
+
+
+type Slug
+    = Slug String
+
+
+
+-- CREATE
+
+
+urlParser : Parser (Slug -> a) a
+urlParser =
+    Url.Parser.custom "SLUG" (\str -> Just (Slug str))
+
+
+decoder : Decoder Slug
+decoder =
+    Decode.map Slug Decode.string
+
+
+
+-- TRANSFORM
+
+
+toString : Slug -> String
+toString (Slug str) =
+    str