docs: add a todo

README.md

@@ -28,6 +28,7 @@ Monkey is an interpreted language written in Go. *This project is still under de
 + Works on 64-bit machines
 + Not production ready yet, need a few more details to be addressed
 + Function that allows for closures
++ Use Go's GC to prevent memory leak
 
 ## Components
 
@@ -59,7 +60,6 @@ Monkey is an interpreted language written in Go. *This project is still under de
 + [ ] check whether we need the token field in AST
 + [ ] test: increase test coverage to at least 80%
 + [ ] chore: dockerize it and publish an image to Docker Hub
-+ [ ] feat: check how to trigger the GC during runtime (in REPL)
 + [ ] feat: return can only be used in functions, do not allow plain return in REPL
 + [ ] feat: if expression with multiple branches
 + [ ] feat: check peek token type in parseExpression
@@ -69,7 +69,6 @@ Monkey is an interpreted language written in Go. *This project is still under de
 + [ ] feat: PrettyPrint, color, AST, etc
 + [ ] feat: sys call such as print(...)
 + [ ] feat: add a helper for available functions
-+ [ ] feat: consider how to write a GC
 + [ ] feat: switch between multiple value representation system using some flag
 + [ ] feat: class (object system)
 + [ ] feat: configuration with yaml or envrc

internal/object/environment.go

@@ -4,9 +4,10 @@ package object
 var _ Environment = (*environment)(nil)
 
 type Environment interface {
+	Keys() []string
 	Get(name string) (Object, bool)
 	Set(name string, val Object)
-	Copy() Environment
+	copy() Environment
 }
 
 type environment struct {
@@ -19,6 +20,19 @@ func NewEnvironment() Environment {
 	}
 }
 
+func NewClosureEnvironment(env Environment) Environment {
+	return env.copy()
+}
+
+func (e *environment) Keys() []string {
+	keys := make([]string, 0, len(e.store))
+	for k := range e.store {
+		keys = append(keys, k)
+	}
+
+	return keys
+}
+
 func (e *environment) Get(name string) (Object, bool) {
 	obj, ok := e.store[name]
 	return obj, ok
@@ -29,7 +43,7 @@ func (e *environment) Set(name string, val Object) {
 }
 
 // return a deep copy of the env
-func (e *environment) Copy() Environment {
+func (e *environment) copy() Environment {
 	env := NewEnvironment()
 	for k, v := range e.store {
 		env.Set(k, v)

internal/object/object.go

@@ -155,15 +155,12 @@ func (e *Error) IsTruthy() bool {
 type Func struct {
 	Parameters []*ast.IdentifierExpression
 	Body       *ast.BlockStatement
-	// the environment for the function scope, allowing closure
-	Env Environment
 }
 
 func NewFunc(params []*ast.IdentifierExpression, body *ast.BlockStatement, env Environment) *Func {
 	return &Func{
 		Parameters: params,
 		Body:       body,
-		Env:        env.Copy(),
 	}
 }
 

internal/repl/repl.go

@@ -41,15 +41,15 @@ type repl struct {
 
 func New(config Config) REPL {
 	return &repl{
-		history: make([]string, config.MaxHistory),
+		history: make([]string, 0, config.MaxHistory),
 	}
 }
 
 func (r *repl) Start(in io.ReadCloser, out io.WriteCloser, userName string) {
 	scanner := bufio.NewScanner(in)
 	l := lexer.New()
 	p := parser.New(l)
-	e := evaluator.New()
+	e := evaluator.New(object.NewEnvironment())
 
 	fmt.Print(MONKEY_FACE)
 	fmt.Printf("Hello %s! This is the Monkey programming language!\n", userName)