some experiments in mixin patterns

src/lang/pyret-lib/experimental/dep-mixins.arr

@@ -0,0 +1,47 @@
+#lang pyret
+
+# Examples as a user
+var todo1: {
+  due: "25 January 2012",
+  task: "Write mixin examples",
+  done: false
+}
+
+fun check(val, expected, message):
+  assert(\(val.equals(expected)), message)
+end
+
+fun assert(testfun, message):
+  var result: testfun()
+  cond:
+    | result => print(message.append(" passed"))
+    | else => print(message.append(" failed"))
+  end
+end
+
+fun doable(todo):
+  todo.{ complete(self): self.{ done : true } end }
+end
+
+var todoable1: doable(todo1)
+check(true, todoable1.complete().done, "todoable worked")
+
+fun make-mutable(obj):
+  var names: builtins.keys(obj)
+  fun make-mutable-field(name, new-obj):
+    var field-val: obj.[name]
+    fun field-method(self, new-val):
+      cond:
+        | is-nothing(new-val) => field-val
+        | else => field-val = new-val      
+      end
+    end
+    new-obj.[name] = field-method._method
+  end
+  names.foldr(make-mutable-field, {})
+end
+
+var mutabletodo1: doable(make-mutable(todo1))
+mutabletodo1.complete()
+mutabletodo1.done()
+