feat: update structure

cs2030s/labs/Lab6/Test4.java

@@ -0,0 +1,92 @@
+import cs2030s.fp.Combiner;
+import cs2030s.fp.Memo;
+
+public class Test4 {
+  public static void main(String[] args) {
+    CS2030STest we = new CS2030STest();
+    
+    Combiner<String, Integer, Integer> concat = (x, y) -> {
+      System.out.println("combine");
+      return x.toString() + y.toString();
+    };
+    
+    Memo<Integer> twenty, thirty, modInt;
+    twenty = Memo.from(() -> 20);
+    thirty = Memo.from(() -> 30);
+    modInt = twenty.combine(thirty, (x, y) -> x * 100 + y);
+    Memo<String> modStr = twenty.combine(thirty, concat);
+    
+    we.expect(
+      "twenty",
+      twenty.toString(),
+      "?"
+    );
+    we.expect(
+      "thirty",
+      thirty.toString(),
+      "?"
+    );
+    we.expect(
+      "modInt",
+      modInt.toString(),
+      "?"
+    );
+    we.expect(
+      "modStr",
+      modStr.toString(),
+      "?"
+    );
+    
+    we.expect(
+      "modStr.get()",
+      modStr.get().toString(),
+      "2030"
+    );
+    
+    we.expect(
+      "twenty",
+      twenty.toString(),
+      "20"
+    );
+    we.expect(
+      "thirty",
+      thirty.toString(),
+      "30"
+    );
+    we.expect(
+      "modInt",
+      modInt.toString(),
+      "?"
+    );
+    
+    Combiner<String, Integer, Double> comb = (x, y) -> x.toString() + " + " + y.toString();
+    Memo<String> s = modInt.combine(Memo.from(0.1), comb);
+    we.expect(
+      "s",
+      s.toString(),
+      "?"
+    );
+    we.expect(
+      "s.get()",
+      s.get(),
+      "2030 + 0.1"
+    );
+    we.expect(
+      "modInt",
+      modInt.toString(),
+      "2030"
+    );
+    
+    Memo<Integer> x1 = Memo.from(1);
+    for (int i = 0; i < 10; i ++) {
+      final Memo<Integer> y1 = x1; // final just to ensure it is unchanged
+      final int j = i;
+      x1 = Memo.from(() -> { System.out.println(j); return y1.get() + y1.get(); });
+    }
+    we.expect(
+      "x.get()",
+      x1.get(),
+      1024
+    );
+  }
+}