Support for empty value / uninitialized variable

src/main/java/com/scriptbasic/executors/operators/AbstractCompareOperator.java

@@ -68,6 +68,10 @@ protected RightValue evaluateOn(final RightValue leftOperand,
                 }
             }
         }
+        if (leftOperand == BasicEmptyValue.EMPTY_VALUE && rightOperand == BasicEmptyValue.EMPTY_VALUE) {
+            return new BasicBooleanValue(compareTo(BasicEmptyValue.EMPTY_VALUE.getNumericValue(),
+                                                   BasicEmptyValue.EMPTY_VALUE.getNumericValue()));
+        }
         throw new BasicRuntimeException("Type mismatch, left operand: " + leftOperand +
                 ", right operand: " + rightOperand);
     }

src/main/java/com/scriptbasic/executors/rightvalues/BasicBooleanValue.java

@@ -27,7 +27,7 @@ private static Boolean convertNumeric(
     public static Boolean asBoolean(final RightValue originalValue) throws BasicRuntimeException {
         final Boolean convertedValue;
 
-        if (originalValue == null) {
+        if (originalValue == null || originalValue == BasicEmptyValue.EMPTY_VALUE) {
             convertedValue = Boolean.FALSE;
         } else if (originalValue instanceof AbstractNumericRightValue) {
             convertedValue = convertNumeric((AbstractNumericRightValue) originalValue);

src/main/java/com/scriptbasic/executors/rightvalues/BasicDoubleValue.java

@@ -52,6 +52,9 @@ public static Double asDouble(final RightValue rv)
             // TODO elaborate the conversion with other object classes, like
             // Long, String...
         }
+        if (rv == BasicEmptyValue.EMPTY_VALUE) {
+            return 0.0;
+        }
         throw new BasicRuntimeException("Can not convert value to double");
     }
 

src/main/java/com/scriptbasic/executors/rightvalues/BasicEmptyValue.java

@@ -0,0 +1,16 @@
+package com.scriptbasic.executors.rightvalues;
+
+public class BasicEmptyValue extends AbstractNumericRightValue<Long, EmptyValue> {
+
+    public static final BasicEmptyValue EMPTY_VALUE = new BasicEmptyValue();
+
+    private BasicEmptyValue() {
+        setValue(EmptyValue.EMPTY_VALUE);
+    }
+
+    @Override
+    public Long getNumericValue() {
+        return 0L;
+    }
+
+}

src/main/java/com/scriptbasic/executors/rightvalues/BasicLongValue.java

@@ -48,6 +48,9 @@ public static Long asLong(final RightValue rv)
             // TODO elaborate the conversion with other object classes, like
             // Double, String...
         }
+        if (rv == BasicEmptyValue.EMPTY_VALUE) {
+            return 0L;
+        }
         throw new BasicRuntimeException("Can not convert value to long");
     }
 

src/main/java/com/scriptbasic/executors/rightvalues/BasicStringValue.java

@@ -12,6 +12,9 @@ public BasicStringValue(final String s) {
     public static String asString(final RightValue rv) throws BasicRuntimeException {
         try {
             final String resultString;
+            if (rv == BasicEmptyValue.EMPTY_VALUE) {
+                return "";
+            }
             if (rv == null
                     || ((AbstractPrimitiveRightValue<Object>) rv).getValue() == null) {
                 resultString = "undef";

src/main/java/com/scriptbasic/executors/rightvalues/EmptyValue.java

@@ -0,0 +1,14 @@
+package com.scriptbasic.executors.rightvalues;
+
+public class EmptyValue {
+
+    public static EmptyValue EMPTY_VALUE = new EmptyValue();
+
+    private EmptyValue() {
+    }
+
+    @Override
+    public String toString() {
+        return "";
+    }
+}

src/main/java/com/scriptbasic/executors/rightvalues/VariableAccess.java

@@ -13,6 +13,9 @@ public RightValue evaluate(final Interpreter interpreter)
             throws ScriptBasicException {
         final VariableMap variableMap = interpreter.getVariables();
         RightValue value = variableMap.getVariableValue(getVariableName());
+        if (value == null) {
+            value = BasicEmptyValue.EMPTY_VALUE;
+        }
         value = interpreter.getHook().variableRead(getVariableName(), value);
         return value;
     }

src/main/java/com/scriptbasic/utility/RightValueUtility.java

@@ -80,6 +80,8 @@ public static RightValue createRightValue(final Object value) {
                     new char[]{(Character) value}));
         } else if (value instanceof Boolean) {
             rightValue = new BasicBooleanValue((Boolean) value);
+        } else if (value == EmptyValue.EMPTY_VALUE) {
+            rightValue = BasicEmptyValue.EMPTY_VALUE;
         } else {
             rightValue = new BasicJavaObjectValue(value);
         }

src/test/java/com/scriptbasic/TestEngine.java

@@ -21,6 +21,7 @@
 
 import static org.junit.jupiter.api.Assertions.assertAll;
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
@@ -514,7 +515,7 @@ public void testSubroutineCallWArgumentsWRetval2() throws Exception {
             final var engine = ScriptBasic.engine();
             engine.eval("sub applePie(b,c)\nglobal a\na = c\nreturn 6\nEndSub");
             engine.subroutine(Long.class, "applePie").call("hello world");
-            assertNull(engine.variable(String.class, "a"));
+            assertNotNull(engine.variable(Object.class, "a"));
         }
 
         @Test
@@ -578,7 +579,7 @@ public void testSubroutineCallWArgumentsWRetval2007() throws Exception {
                     "EndSub");
             final var sub = engine.subroutine(null, "applePie");
             sub.call("hello world");
-            assertGlobalVariableIsNotDefined(engine, "a");
+            assertNotNull(engine.variable(Object.class, "a"));
         }
 
         @Test
@@ -599,7 +600,7 @@ public void testSubroutineCallWArgumentsWRetval007() throws Exception {
         }
 
         private void assertGlobalVariableIsNotDefined(final ScriptBasic engine, final String name) throws ScriptBasicException {
-            assertNull(engine.variable(Object.class, "a"));
+            assertNull(engine.variable(Object.class, name));
         }
 
         @Test

src/test/java/com/scriptbasic/executors/operators/TestOperators.java

@@ -121,6 +121,18 @@ public void testOperators() throws AnalysisException,
         a("a= 3.0 <> \"a\"", true);
         a("a= true = \"a\"", false);
 
+        // Comparison with uninitialized/empty variable
+        a("a= b = \"\"", true);
+        a("a= b = 0", true);
+        a("a= b = \"x\"", false);
+        a("a= b = 1", false);
+        a("a= b = c", true);
+        a("a= b <> c", false);
+        a("a= b < c", false);
+        a("a= b > c", false);
+        a("a= b <= c", true);
+        a("a= b >= c", true);
+
         a("a= \"x\" <> \"x\"", false);
         a("a= \"x\" <> \"y\"", true);
         a("a= \"x\" < \"y\"", true);

src/test/java/com/scriptbasic/testprograms/TestPrograms.java

@@ -91,7 +91,7 @@ public void testPrograms() throws Exception {
         }
         codeTest("TestSub1.bas", "6");
         codeTest("TestSub2.bas", "21");
-        codeTest("TestSub3.bas", "21undef");
+        codeTest("TestSub3.bas", "21");
         codeTest("TestSub4.bas", "123\n123\n123\n123\n");
         codeTest("TestSub5.bas", "1111");
         codeTest("TestWhile1.bas", "89");
@@ -126,7 +126,7 @@ public void testPrograms() throws Exception {
         codeTest("TestForLoop9.bas", "111213212223313233");
         codeTest("TestForLoop10.bas", "12323");
         codeTest("TestRuntimeFunction.bas", "1.01.5707963267948966");
-        codeTest("TestNullFunction.bas", "undefundef");
+        codeTest("TestNullFunction.bas", "undef");
         codeTest("TestMethodCall.bas",
             "" + Math.sin(1.0) + "\n" + Math.sin(1.0));
         map = new HashMap<>();
@@ -135,7 +135,7 @@ public void testPrograms() throws Exception {
 
         testRuntimeFail("TestBadArray1.bas");
         codeTest("TestBadArray2.bas", "");
-        codeTest("TestBadArray3.bas", "");
+        testRuntimeFail("TestBadArray3.bas");
         codeTest("BubbleSort.bas", "-1\n0\n2\n3\n7\n58\n99\n");
         codeTest("TestAbs.bas", "131355.377.7");
         codeTest("TestChomp.bas", "ttt");