assert and test changes

compiler/compiler.go

@@ -91,9 +91,7 @@ func (c *Compiler) Compile(node ast.Node) error {
 			return err
 		}
 
-		if !c.lastInstructionIs(code.OpNoop) {
-			c.emit(code.OpPop)
-		}
+		c.emit(code.OpPop)
 
 	case *ast.InfixExpression:
 		if node.Operator == "<" || node.Operator == "<=" {
@@ -182,9 +180,6 @@ func (c *Compiler) Compile(node ast.Node) error {
 		}
 
 	case *ast.IfExpression:
-		if c.lastInstructionIs(code.OpPop) {
-			c.removeLastPop()
-		}
 		c.l++
 		err := c.Compile(node.Condition)
 		c.l--
@@ -240,6 +235,14 @@ func (c *Compiler) Compile(node ast.Node) error {
 		}
 		c.l--
 
+		if c.lastInstructionIs(code.OpPop) {
+			c.removeLastPop()
+		} else {
+			if !c.lastInstructionIs(code.OpReturn) {
+				c.emit(code.OpNull)
+			}
+		}
+
 	case *ast.AssignmentStatement:
 		symbol, ok := c.symbolTable.Resolve(node.Name.Value)
 		if !ok {
@@ -366,8 +369,13 @@ func (c *Compiler) Compile(node ast.Node) error {
 		if c.lastInstructionIs(code.OpPop) {
 			c.replaceLastPopWithReturn()
 		}
+
+		// If the function doesn't end with a return statement add one with a
+		// `return null;` and also handle the edge-case of empty functions.
 		if !c.lastInstructionIs(code.OpReturn) {
-			c.emit(code.OpNull)
+			if !c.lastInstructionIs(code.OpNull) {
+				c.emit(code.OpNull)
+			}
 			c.emit(code.OpReturn)
 		}