further improvements

internal/vm/vm_test.go

@@ -130,7 +130,7 @@ func testExpectedObject(t *testing.T, expected interface{}, actual object.Object
 		}
 
 	case object.Null:
-		if actual != Null {
+		if actual != object.NULL {
 			t.Errorf("object is not Null: %T (%+v)", actual, actual)
 		}
 
@@ -302,14 +302,14 @@ func TestConditionals(t *testing.T) {
 		{"if (1 < 2) { 10 }", 10},
 		{"if (1 < 2) { 10 } else { 20 }", 10},
 		{"if (1 > 2) { 10 } else { 20 }", 20},
-		{"if (1 > 2) { 10 }", Null},
-		{"if (false) { 10 }", Null},
+		{"if (1 > 2) { 10 }", object.NULL},
+		{"if (false) { 10 }", object.NULL},
 		{"if ((if (false) { 10 })) { 10 } else { 20 }", 20},
-		{"if (true) { a := 5; }", Null},
-		{"if (true) { 10; a := 5; }", Null},
-		{"if (false) { 10 } else { b := 5; }", Null},
-		{"if (false) { 10 } else { 10; b := 5; }", Null},
-		{"if (true) { a := 5; } else { 10 }", Null},
+		{"if (true) { a := 5; }", object.NULL},
+		{"if (true) { 10; a := 5; }", object.NULL},
+		{"if (false) { 10 } else { b := 5; }", object.NULL},
+		{"if (false) { 10 } else { 10; b := 5; }", object.NULL},
+		{"if (true) { a := 5; } else { 10 }", object.NULL},
 		{"x := 0; if (true) { x = 1; }; if (false) { x = 2; }; x", 1},
 		{"if (1 < 2) { 10 } else if (1 == 2) { 20 }", 10},
 		{"if (1 > 2) { 10 } else if (1 == 2) { 20 } else { 30 }", 30},
@@ -430,13 +430,13 @@ func TestIndexExpressions(t *testing.T) {
 		{"[1, 2, 3][1]", 2},
 		{"[1, 2, 3][0 + 2]", 3},
 		{"[[1, 1, 1]][0][0]", 1},
-		{"[][0]", Null},
-		{"[1, 2, 3][99]", Null},
-		{"[1][-1]", Null},
+		{"[][0]", object.NULL},
+		{"[1, 2, 3][99]", object.NULL},
+		{"[1][-1]", object.NULL},
 		{"{1: 1, 2: 2}[1]", 1},
 		{"{1: 1, 2: 2}[2]", 2},
-		{"{1: 1}[0]", Null},
-		{"{}[0]", Null},
+		{"{1: 1}[0]", object.NULL},
+		{"{}[0]", object.NULL},
 		{`"abc"[0]`, "a"},
 		{`"abc"[1]`, "b"},
 		{`"abc"[2]`, "c"},
@@ -506,7 +506,7 @@ func TestFunctionsWithoutReturnValue(t *testing.T) {
         noReturn := fn() { };
         noReturn();
         `,
-			expected: Null,
+			expected: object.NULL,
 		},
 		{
 			input: `
@@ -515,7 +515,7 @@ func TestFunctionsWithoutReturnValue(t *testing.T) {
         noReturn();
         noReturnTwo();
         `,
-			expected: Null,
+			expected: object.NULL,
 		},
 	}
 
@@ -724,16 +724,16 @@ func TestBuiltinFunctions(t *testing.T) {
 		},
 		{`len([1, 2, 3])`, 3},
 		{`len([])`, 0},
-		{`print("hello", "world!")`, Null},
+		{`print("hello", "world!")`, object.NULL},
 		{`first([1, 2, 3])`, 1},
-		{`first([])`, Null},
+		{`first([])`, object.NULL},
 		{`first(1)`,
 			&object.Error{
 				Message: "TypeError: first() expected argument #1 to be `array` got `int`",
 			},
 		},
 		{`last([1, 2, 3])`, 3},
-		{`last([])`, Null},
+		{`last([])`, object.NULL},
 		{`last(1)`,
 			&object.Error{
 				Message: "TypeError: last() expected argument #1 to be `array` got `int`",