feat(objectionary#86): add one more puzzle

src/main/java/org/eolang/opeo/ast/InstanceField.java

@@ -72,6 +72,11 @@ public Iterable<Directive> toXmir() {
 
     @Override
     public List<AstNode> opcodes() {
+        //@checkstyle MethodBodyCommentsCheck (10 lines)
+        // @todo #86:90min Implement "GETFIELD" opcode compilation from 'InstanceField'.
+        //  The opcode should be compiled from the 'InstanceField' node correctly.
+        //  Right now we put dummy owner and descriptor.
+        //  Don't forget to remove this comment after the implementation is done and add new tests.
         final List<AstNode> res = new ArrayList<>(0);
         res.addAll(this.source.opcodes());
         res.add(new Opcode(Opcodes.GETFIELD, "???owner???", this.name, "???descriptor???"));

src/main/java/org/eolang/opeo/ast/Literal.java

@@ -61,7 +61,13 @@ public List<AstNode> opcodes() {
         } else if (this.object instanceof String) {
             result = Collections.singletonList(Literal.opcode((String) this.object));
         } else {
-            throw new UnsupportedOperationException("Not implemented yet");
+            throw new IllegalArgumentException(
+                String.format(
+                    "Unsupported literal type %s, value is %s",
+                    this.object.getClass().getName(),
+                    this.object
+                )
+            );
         }
         return result;
     }

src/main/java/org/eolang/opeo/ast/Reference.java

@@ -74,6 +74,6 @@ public Iterable<Directive> toXmir() {
 
     @Override
     public List<AstNode> opcodes() {
-        throw new UnsupportedOperationException("Not implemented yet");
+        return this.ref.get().opcodes();
     }
 }