Eksami alusosa harjutuse lahendus

Author: sim642

sols/proovieksam/EstologEvaluator.java

@@ -0,0 +1,72 @@
+package proovieksam;
+
+import proovieksam.ast.*;
+
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.NoSuchElementException;
+
+import static proovieksam.ast.EstologNode.*;
+
+public class EstologEvaluator {
+    private final Map<String, Boolean> env = new HashMap<>();
+
+    public static boolean eval(EstologProg prog) {
+        EstologEvaluator estologEvaluator = new EstologEvaluator();
+        return estologEvaluator.evalNode(prog);
+    }
+
+    private boolean evalNode(EstologNode node) {
+        return switch (node) {
+            case EstologLiteraal(boolean value) -> value;
+            case EstologMuutuja(String nimi) -> {
+                Boolean value = env.get(nimi);
+                if (value == null)
+                    throw new NoSuchElementException("Undefined variable " + nimi);
+                else
+                    yield value;
+            }
+            case EstologJa(EstologNode left, EstologNode right) ->
+                    evalNode(left) && evalNode(right);
+            case EstologVoi(EstologNode left, EstologNode right) ->
+                    evalNode(left) || evalNode(right);
+            case EstologVordus(EstologNode left, EstologNode right) ->
+                    evalNode(left) == evalNode(right);
+            case EstologKui(EstologNode kui, EstologNode siis, EstologNode muidu) -> {
+                if (evalNode(kui)) {
+                    yield evalNode(siis);
+                }
+                else if (muidu != null) {
+                    yield evalNode(muidu);
+                }
+                else {
+                    yield true; // kui MUIDU avaldis on puudu, tagastame true
+                }
+            }
+            case EstologDef(String nimi, EstologNode avaldis) -> {
+                env.put(nimi, evalNode(avaldis));
+                yield false; // ei kasutata
+            }
+            case EstologProg(EstologNode avaldis, List<EstologDef> defs) -> {
+                for (EstologDef def : defs)
+                    evalNode(def);
+                yield evalNode(avaldis);
+            }
+        };
+    }
+
+    static void main() {
+        EstologProg prog = prog(
+                kui(vordus(var("x"), var("y")), var("a"), var("b")),
+
+                def("x", lit(false)),
+                def("y", lit(true)),
+                def("a", ja(var("x"), var("y"))),
+                def("b", voi(var("x"), var("y")))
+        );
+
+        System.out.println(prog);
+        System.out.println(eval(prog));
+    }
+}