WIP: Add methods for querying JSON values

TODO: write description here.

This fixes #356.

Changelog: added

std/src/std/json.inko

@@ -194,6 +194,63 @@ impl ToString for Error {
   }
 }
 
+class pub Query {
+  let @value: Option[ref Json]
+
+  fn pub move key(name: String) -> Query {
+    @value = match ref @value {
+      case Some(Object(v)) -> v.opt(name)
+      case _ -> Option.None
+    }
+
+    self
+  }
+
+  fn pub move index(index: Int) -> Query {
+    @value = match ref @value {
+      case Some(Array(v)) -> v.opt(index)
+      case _ -> Option.None
+    }
+
+    self
+  }
+
+  fn pub string -> Option[String] {
+    match @value {
+      case Some(String(v)) -> Option.Some(v)
+      case _ -> Option.None
+    }
+  }
+
+  fn pub int -> Option[Int] {
+    match @value {
+      case Some(Int(v)) -> Option.Some(v)
+      case _ -> Option.None
+    }
+  }
+
+  fn pub float -> Option[Float] {
+    match @value {
+      case Some(Float(v)) -> Option.Some(v)
+      case _ -> Option.None
+    }
+  }
+
+  fn pub object -> Option[ref Map[String, Json]] {
+    match @value {
+      case Some(Object(v)) -> Option.Some(v)
+      case _ -> Option.None
+    }
+  }
+
+  fn pub array -> Option[ref Array[Json]] {
+    match @value {
+      case Some(Array(v)) -> Option.Some(v)
+      case _ -> Option.None
+    }
+  }
+}
+
 # A JSON value, such as `true` or an array.
 class pub enum Json {
   case Int(Int)
@@ -237,6 +294,18 @@ class pub enum Json {
   fn pub to_pretty_string -> String {
     Generator.new(DEFAULT_PRETTY_INDENT).generate(self)
   }
+
+  fn pub query -> Query {
+    Query { @value = Option.Some(self) }
+  }
+
+  fn pub key(name: String) -> Query {
+    query.key(name)
+  }
+
+  fn pub index(index: Int) -> Query {
+    query.index(index)
+  }
 }
 
 impl ToString for Json {