Add example from lkuper's intern talk to the test suite.

Author: lkuper

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

@@ -0,0 +1,54 @@
+// Example from lkuper's intern talk, August 2012.
+
+trait Equal {
+    fn isEq(a: self) -> bool;
+}
+
+enum Color { cyan, magenta, yellow, black }
+
+impl Color : Equal {
+    fn isEq(a: Color) -> bool {
+        match (self, a) {
+          (cyan, cyan)       => { true  }
+          (magenta, magenta) => { true  }
+          (yellow, yellow)   => { true  }
+          (black, black)     => { true  }
+          _                  => { false }
+        }
+    }
+}
+
+enum ColorTree {
+    leaf(Color),
+    branch(@ColorTree, @ColorTree)
+}
+
+impl ColorTree : Equal {
+    fn isEq(a: ColorTree) -> bool {
+        match (self, a) {
+          (leaf(x), leaf(y)) => { x.isEq(y) }
+          (branch(l1, r1), branch(l2, r2)) => { 
+            (*l1).isEq(*l2) && (*r1).isEq(*r2)
+          }
+          _ => { false }
+        }
+    }
+}
+
+fn main() {
+    assert cyan.isEq(cyan);
+    assert magenta.isEq(magenta);
+    assert !cyan.isEq(yellow);
+    assert !magenta.isEq(cyan);
+
+    assert leaf(cyan).isEq(leaf(cyan));
+    assert !leaf(cyan).isEq(leaf(yellow));
+
+    assert branch(@leaf(magenta), @leaf(cyan))
+        .isEq(branch(@leaf(magenta), @leaf(cyan)));
+
+    assert !branch(@leaf(magenta), @leaf(cyan))
+        .isEq(branch(@leaf(magenta), @leaf(magenta)));
+
+    log(error, "Assertions all succeeded!");
+}