Add Set example

example/set.wren

@@ -0,0 +1,102 @@
+class Set {
+  new {
+    _list = []
+    _clean = true
+  }
+  
+  new (list) {
+    if (list is List) {
+      _list = list
+      _clean = false
+      cleanup
+    } // raise error?
+  }
+  
+  cleanup {
+    // Removes duplicates in the underlying list.
+    if (!_clean) {
+      var newList = []
+      for (element in _list) {
+        if (!newList.contains(element)) newList.add(element)
+      }
+      _list = newList
+      _clean = true
+    }
+  }
+
+  add (element) {
+    _clean = false
+    _list.add(element)
+  }
+  
+  remove (element) {
+    cleanup // Remove duplicates, so we can return early upon deletion.
+    for (i in 0.._list.count) {
+      if (_list[i] == element) {
+        _list.removeAt(i)
+        return
+      }
+    }
+  }
+  
+  contains (element) {
+    return _list.contains(element)
+  }
+
+  count {
+    cleanup
+    return _list.count
+  }
+  
+  // I'm not sure on these:
+  iterate (i) {
+    cleanup
+    if (i < count || i >= count) return false  
+    return i + 1
+  }
+  
+  iteratorValue (i) {
+    cleanup
+    return _list[i]
+  }
+
+  map (f) {
+    return new Set(_list.map(f))
+  }
+  
+  where (f) {
+    return new Set(_list.where(f))
+  }
+  
+  /*| that {
+    // Union
+
+  }*/
+  
+  + that {
+    // A synonym for |
+    return new Set(_list + that)
+    // return this | that
+  }
+  
+  /* & that {
+    // Intersection
+    return new Set(
+      _list.where(fn (element) { 
+        return that.contains(element)
+      }) + that.where(fn (element) {
+        return _list.contains(element)
+      })
+    )
+  } */ 
+  
+  - that {
+    // Set minus
+    return new Set(
+      _list.where(
+        fn (element) {
+          return (
+              !that.contains(element))
+        }))
+  }
+}