Example from lkuper's intern talk, but now with static methods!

Author: lkuper

src/test/run-pass/typeclasses-eq-example-static.rs

@@ -0,0 +1,55 @@
+// Example from lkuper's intern talk, August 2012 -- now with static
+// methods!
+
+trait Equal {
+    static fn isEq(a: self, b: self) -> bool;
+}
+
+enum Color { cyan, magenta, yellow, black }
+
+impl Color : Equal {
+    static fn isEq(a: Color, b: Color) -> bool {
+        match (a, b) {
+          (cyan, cyan)       => { true  }
+          (magenta, magenta) => { true  }
+          (yellow, yellow)   => { true  }
+          (black, black)     => { true  }
+          _                  => { false }
+        }
+    }
+}
+
+enum ColorTree {
+    leaf(Color),
+    branch(@ColorTree, @ColorTree)
+}
+
+impl ColorTree : Equal {
+    static fn isEq(a: ColorTree, b: ColorTree) -> bool {
+        match (a, b) {
+          (leaf(x), leaf(y)) => { isEq(x, y) }
+          (branch(l1, r1), branch(l2, r2)) => { 
+            isEq(*l1, *l2) && isEq(*r1, *r2)
+          }
+          _ => { false }
+        }
+    }
+}
+
+fn main() {
+    assert isEq(cyan, cyan);
+    assert isEq(magenta, magenta);
+    assert !isEq(cyan, yellow);
+    assert !isEq(magenta, cyan);
+
+    assert isEq(leaf(cyan), leaf(cyan));
+    assert !isEq(leaf(cyan), leaf(yellow));
+
+    assert isEq(branch(@leaf(magenta), @leaf(cyan)),
+                branch(@leaf(magenta), @leaf(cyan)));
+
+    assert !isEq(branch(@leaf(magenta), @leaf(cyan)),
+                 branch(@leaf(magenta), @leaf(magenta)));
+
+    log(error, "Assertions all succeeded!");
+}