fixed mutability

compiler/compiler.go

@@ -210,13 +210,11 @@ func (c *Compiler) Compile(node ast.Node) error {
 		}
 
 		if symbol.Scope == GlobalScope {
-			c.emit(code.OpGetGlobal, symbol.Index)
+			c.emit(code.OpAssignGlobal, symbol.Index)
 		} else {
-			c.emit(code.OpGetLocal, symbol.Index)
+			c.emit(code.OpAssignLocal, symbol.Index)
 		}
 
-		c.emit(code.OpAssign)
-
 	case *ast.LetStatement:
 		symbol, ok := c.symbolTable.Resolve(node.Name.Value)
 		if !ok {