diff --git a/internal/builtins/hash.go b/internal/builtins/hash.go
index 072be42..eb84d6a 100644
--- a/internal/builtins/hash.go
+++ b/internal/builtins/hash.go
@@ -14,8 +14,8 @@ func HashOf(args ...object.Object) object.Object {
 		return newError(err.Error())
 	}
 
-	if hash, ok := args[0].(object.Hashable); ok {
-		return object.Integer{Value: int64(hash.HashKey().Value)}
+	if hash, ok := args[0].(object.Hasher); ok {
+		return object.Integer{Value: int64(hash.Hash().Value)}
 	}
 
 	return newError("TypeError: hash() expected argument #1 to be hashable")
diff --git a/internal/evaluator/evaluator.go b/internal/evaluator/evaluator.go
index 75752b2..1e156e1 100644
--- a/internal/evaluator/evaluator.go
+++ b/internal/evaluator/evaluator.go
@@ -61,8 +61,8 @@ func Eval(node ast.Node, env *object.Environment) object.Object {
 		}
 
 		if ident, ok := node.Left.(*ast.Identifier); ok {
-			if immutable, ok := value.(object.Immutable); ok {
-				env.Set(ident.Value, immutable.Clone())
+			if obj, ok := value.(object.Copyable); ok {
+				env.Set(ident.Value, obj.Copy())
 			} else {
 				env.Set(ident.Value, value)
 			}
@@ -105,8 +105,8 @@ func Eval(node ast.Node, env *object.Environment) object.Object {
 				if isError(key) {
 					return key
 				}
-				if hashKey, ok := key.(object.Hashable); ok {
-					hashed := hashKey.HashKey()
+				if hashKey, ok := key.(object.Hasher); ok {
+					hashed := hashKey.Hash()
 					hash.Pairs[hashed] = object.HashPair{Key: key, Value: value}
 				} else {
 					return newError("cannot index hash with %T", key)
@@ -630,12 +630,12 @@ func evalStringIndexExpression(str, index object.Object) object.Object {
 func evalHashIndexExpression(hash, index object.Object) object.Object {
 	hashObject := hash.(*object.Hash)
 
-	key, ok := index.(object.Hashable)
+	key, ok := index.(object.Hasher)
 	if !ok {
 		return newError("unusable as hash key: %s", index.Type())
 	}
 
-	pair, ok := hashObject.Pairs[key.HashKey()]
+	pair, ok := hashObject.Pairs[key.Hash()]
 	if !ok {
 		return NULL
 	}
@@ -664,7 +664,7 @@ func evalHashLiteral(node *ast.HashLiteral, env *object.Environment) object.Obje
 			return key
 		}
 
-		hashKey, ok := key.(object.Hashable)
+		hashKey, ok := key.(object.Hasher)
 		if !ok {
 			return newError("unusable as hash key: %s", key.Type())
 		}
@@ -674,7 +674,7 @@ func evalHashLiteral(node *ast.HashLiteral, env *object.Environment) object.Obje
 			return value
 		}
 
-		hashed := hashKey.HashKey()
+		hashed := hashKey.Hash()
 		pairs[hashed] = object.HashPair{
 			Key:   key,
 			Value: value,
diff --git a/internal/evaluator/evaluator_test.go b/internal/evaluator/evaluator_test.go
index 6260be7..4c5d78a 100644
--- a/internal/evaluator/evaluator_test.go
+++ b/internal/evaluator/evaluator_test.go
@@ -640,12 +640,12 @@ func TestHashLiterals(t *testing.T) {
 	}
 
 	expected := map[object.HashKey]int64{
-		(object.String{Value: "one"}).HashKey():   1,
-		(object.String{Value: "two"}).HashKey():   2,
-		(object.String{Value: "three"}).HashKey(): 3,
-		(object.Integer{Value: 4}).HashKey():      4,
-		TRUE.HashKey():                            5,
-		FALSE.HashKey():                           6,
+		(object.String{Value: "one"}).Hash():   1,
+		(object.String{Value: "two"}).Hash():   2,
+		(object.String{Value: "three"}).Hash(): 3,
+		(object.Integer{Value: 4}).Hash():      4,
+		TRUE.Hash():                            5,
+		FALSE.Hash():                           6,
 	}
 
 	if len(result.Pairs) != len(expected) {
@@ -671,8 +671,8 @@ func TestHashMerging(t *testing.T) {
 	}
 
 	expected := map[object.HashKey]int64{
-		(object.String{Value: "a"}).HashKey(): 1,
-		(object.String{Value: "b"}).HashKey(): 2,
+		(object.String{Value: "a"}).Hash(): 1,
+		(object.String{Value: "b"}).Hash(): 2,
 	}
 
 	if len(result.Pairs) != len(expected) {
diff --git a/internal/object/bool.go b/internal/object/bool.go
index 7c06f35..6ad3977 100644
--- a/internal/object/bool.go
+++ b/internal/object/bool.go
@@ -32,10 +32,24 @@ func (b Boolean) Inspect() string {
 	return fmt.Sprintf("%t", b.Value)
 }
 
-func (b Boolean) Clone() Object {
+// Copy implements the Copyable interface
+func (b Boolean) Copy() Object {
 	return Boolean{Value: b.Value}
 }
 
+// Hash implements the Hasher interface
+func (b Boolean) Hash() HashKey {
+	var value uint64
+
+	if b.Value {
+		value = 1
+	} else {
+		value = 0
+	}
+
+	return HashKey{Type: b.Type(), Value: value}
+}
+
 func (b Boolean) String() string {
 	return b.Inspect()
 }
diff --git a/internal/object/environment.go b/internal/object/environment.go
index 7d98b4c..60491d1 100644
--- a/internal/object/environment.go
+++ b/internal/object/environment.go
@@ -4,24 +4,31 @@ import "unicode"
 
 func NewEnclosedEnvironment(outer *Environment) *Environment {
 	env := NewEnvironment()
-	env.outer = outer
+	env.parent = outer
 	return env
 }
 
 func NewEnvironment() *Environment {
 	s := make(map[string]Object)
-	return &Environment{store: s, outer: nil}
+	return &Environment{store: s, parent: nil}
 }
 
 type Environment struct {
-	store map[string]Object
-	outer *Environment
+	store  map[string]Object
+	parent *Environment
+}
+
+// New creates a new copy of the environment with the current environment as parent
+func (e *Environment) New() *Environment {
+	env := NewEnvironment()
+	env.parent = e
+	return env
 }
 
 func (e *Environment) Get(name string) (Object, bool) {
 	obj, ok := e.store[name]
-	if !ok && e.outer != nil {
-		obj, ok = e.outer.Get(name)
+	if !ok && e.parent != nil {
+		obj, ok = e.parent.Get(name)
 	}
 	return obj, ok
 }
@@ -40,7 +47,7 @@ func (e *Environment) ExportedHash() *Hash {
 	for k, v := range e.store {
 		if unicode.IsUpper(rune(k[0])) {
 			s := String{Value: k}
-			pairs[s.HashKey()] = HashPair{Key: s, Value: v}
+			pairs[s.Hash()] = HashPair{Key: s, Value: v}
 		}
 	}
 	return &Hash{Pairs: pairs}
diff --git a/internal/object/error.go b/internal/object/error.go
index c06d632..33d64c5 100644
--- a/internal/object/error.go
+++ b/internal/object/error.go
@@ -18,7 +18,8 @@ func (e Error) Inspect() string {
 	return "Error: " + e.Message
 }
 
-func (e Error) Clone() Object {
+// Copy implements the Copyable interface
+func (e Error) Copy() Object {
 	return Error{Message: e.Message}
 }
 
diff --git a/internal/object/hash.go b/internal/object/hash.go
index 6ef3a39..e0d24c4 100644
--- a/internal/object/hash.go
+++ b/internal/object/hash.go
@@ -3,7 +3,6 @@ package object
 import (
 	"bytes"
 	"fmt"
-	"hash/fnv"
 	"strings"
 )
 
@@ -12,29 +11,6 @@ type HashKey struct {
 	Value uint64
 }
 
-func (b Boolean) HashKey() HashKey {
-	var value uint64
-
-	if b.Value {
-		value = 1
-	} else {
-		value = 0
-	}
-
-	return HashKey{Type: b.Type(), Value: value}
-}
-
-func (i Integer) HashKey() HashKey {
-	return HashKey{Type: i.Type(), Value: uint64(i.Value)}
-}
-
-func (s String) HashKey() HashKey {
-	h := fnv.New64a()
-	h.Write([]byte(s.Value))
-
-	return HashKey{Type: s.Type(), Value: h.Sum64()}
-}
-
 type HashPair struct {
 	Key   Object
 	Value Object
@@ -91,12 +67,12 @@ func (h *Hash) Add(other Object) (Object, error) {
 }
 
 func (h *Hash) Get(index Object) (Object, error) {
-	key, ok := index.(Hashable)
+	key, ok := index.(Hasher)
 	if !ok {
 		return nil, fmt.Errorf("invalid hash key %s", index.Type())
 	}
 
-	pair, found := h.Pairs[key.HashKey()]
+	pair, found := h.Pairs[key.Hash()]
 	if !found {
 		return Null{}, nil
 	}
@@ -105,12 +81,12 @@ func (h *Hash) Get(index Object) (Object, error) {
 }
 
 func (h *Hash) Set(index, other Object) error {
-	key, ok := index.(Hashable)
+	key, ok := index.(Hasher)
 	if !ok {
 		return fmt.Errorf("invalid hash key %s", index.Type())
 	}
 
-	h.Pairs[key.HashKey()] = HashPair{Key: index, Value: other}
+	h.Pairs[key.Hash()] = HashPair{Key: index, Value: other}
 
 	return nil
 }
@@ -122,8 +98,8 @@ func (h *Hash) Compare(other Object) int {
 		}
 		for _, pair := range h.Pairs {
 			left := pair.Value
-			hashed := left.(Hashable)
-			right, ok := obj.Pairs[hashed.HashKey()]
+			hashed := left.(Hasher)
+			right, ok := obj.Pairs[hashed.Hash()]
 			if !ok {
 				return -1
 			}
diff --git a/internal/object/int.go b/internal/object/int.go
index 2720028..3ffcd7c 100644
--- a/internal/object/int.go
+++ b/internal/object/int.go
@@ -18,10 +18,15 @@ func (i Integer) Inspect() string {
 	return fmt.Sprintf("%d", i.Value)
 }
 
-func (i Integer) Clone() Object {
+func (i Integer) Copy() Object {
 	return Integer{Value: i.Value}
 }
 
+// Hash implements the Hasher interface
+func (i Integer) Hash() HashKey {
+	return HashKey{Type: i.Type(), Value: uint64(i.Value)}
+}
+
 func (i Integer) String() string {
 	return i.Inspect()
 }
diff --git a/internal/object/module.go b/internal/object/module.go
index 67a068b..217798e 100644
--- a/internal/object/module.go
+++ b/internal/object/module.go
@@ -25,12 +25,12 @@ func (m Module) Inspect() string {
 }
 
 func (m Module) Get(index Object) (Object, error) {
-	key, ok := index.(Hashable)
+	key, ok := index.(Hasher)
 	if !ok {
 		return nil, fmt.Errorf("invalid module attribute %s", index.Type())
 	}
 
-	attr, found := m.Attrs.(*Hash).Pairs[key.HashKey()]
+	attr, found := m.Attrs.(*Hash).Pairs[key.Hash()]
 	if !found {
 		return Null{}, nil
 	}
diff --git a/internal/object/object.go b/internal/object/object.go
index 1ee0abb..614f683 100644
--- a/internal/object/object.go
+++ b/internal/object/object.go
@@ -54,17 +54,14 @@ func (t Type) String() string {
 	}
 }
 
-// Comparable is the interface for comparing two Object and their underlying
-// values. It is the responsibility of the caller (left) to check for types.
-// Returns `true` iif the types and values are identical, `false` otherwise.
+// Comparable is the interface for objects to implement suitable comparisons
 type Comparable interface {
 	Compare(other Object) int
 }
 
-// Immutable is the interface for all immutable objects which must implement
-// the Clone() method used by binding names to values.
-type Immutable interface {
-	Clone() Object
+// Copyable is the interface for creating copies of objects
+type Copyable interface {
+	Copy() Object
 }
 
 // Object represents a value and implementations are expected to implement
@@ -76,10 +73,9 @@ type Object interface {
 	Inspect() string
 }
 
-// Hashable is the interface for all hashable objects which must implement
-// the HashKey() method which returns a HashKey result.
-type Hashable interface {
-	HashKey() HashKey
+// Hasher is the interface for objects to provide suitable hash keys
+type Hasher interface {
+	Hash() HashKey
 }
 
 // BuiltinFunction represents the builtin function type
diff --git a/internal/object/object_test.go b/internal/object/object_test.go
index b74aa87..191c225 100644
--- a/internal/object/object_test.go
+++ b/internal/object/object_test.go
@@ -8,15 +8,15 @@ func TestStringHashKey(t *testing.T) {
 	diff1 := String{Value: "My name is johnny"}
 	diff2 := String{Value: "My name is johnny"}
 
-	if hello1.HashKey() != hello2.HashKey() {
+	if hello1.Hash() != hello2.Hash() {
 		t.Errorf("string with same content have different hash keys")
 	}
 
-	if diff1.HashKey() != diff2.HashKey() {
+	if diff1.Hash() != diff2.Hash() {
 		t.Errorf("string with same content have different hash keys")
 	}
 
-	if hello1.HashKey() == diff1.HashKey() {
+	if hello1.Hash() == diff1.Hash() {
 		t.Errorf("string with different content have same hash keys")
 	}
 }
diff --git a/internal/object/str.go b/internal/object/str.go
index 1faccca..dc27118 100644
--- a/internal/object/str.go
+++ b/internal/object/str.go
@@ -2,6 +2,7 @@ package object
 
 import (
 	"fmt"
+	"hash/fnv"
 	"strings"
 	"unicode/utf8"
 )
@@ -26,10 +27,18 @@ func (s String) Inspect() string {
 	return fmt.Sprintf("%#v", s.Value)
 }
 
-func (s String) Clone() Object {
+func (s String) Copy() Object {
 	return String{Value: s.Value}
 }
 
+// Hash implements the Hasher interface
+func (s String) Hash() HashKey {
+	h := fnv.New64a()
+	h.Write([]byte(s.Value))
+
+	return HashKey{Type: s.Type(), Value: h.Sum64()}
+}
+
 func (s String) String() string {
 	return s.Value
 }
diff --git a/internal/vm/vm.go b/internal/vm/vm.go
index bea2809..b8f8fb5 100644
--- a/internal/vm/vm.go
+++ b/internal/vm/vm.go
@@ -102,7 +102,7 @@ func (s *VMState) ExportedHash() *object.Hash {
 			if symbol.Scope == compiler.GlobalScope {
 				obj := s.Globals[symbol.Index]
 				s := object.String{Value: name}
-				pairs[s.HashKey()] = object.HashPair{Key: s, Value: obj}
+				pairs[s.Hash()] = object.HashPair{Key: s, Value: obj}
 			}
 		}
 	}
@@ -210,8 +210,8 @@ func (vm *VM) executeSetGlobal() error {
 	globalIndex := vm.currentFrame().ReadUint16()
 
 	ref := vm.pop()
-	if immutable, ok := ref.(object.Immutable); ok {
-		vm.state.Globals[globalIndex] = immutable.Clone()
+	if obj, ok := ref.(object.Copyable); ok {
+		vm.state.Globals[globalIndex] = obj.Copy()
 	} else {
 		vm.state.Globals[globalIndex] = ref
 	}
@@ -223,8 +223,8 @@ func (vm *VM) executeSetLocal() error {
 	localIndex := vm.currentFrame().ReadUint8()
 
 	ref := vm.pop()
-	if immutable, ok := ref.(object.Immutable); ok {
-		vm.stack[vm.currentFrame().basePointer+int(localIndex)] = immutable.Clone()
+	if obj, ok := ref.(object.Copyable); ok {
+		vm.stack[vm.currentFrame().basePointer+int(localIndex)] = obj.Copy()
 	} else {
 		vm.stack[vm.currentFrame().basePointer+int(localIndex)] = ref
 	}
@@ -241,12 +241,12 @@ func (vm *VM) buildHash(startIndex, endIndex int) (object.Object, error) {
 
 		pair := object.HashPair{Key: key, Value: value}
 
-		hashKey, ok := key.(object.Hashable)
+		hashKey, ok := key.(object.Hasher)
 		if !ok {
 			return nil, fmt.Errorf("unusable as hash key: %s", key.Type())
 		}
 
-		hashedPairs[hashKey.HashKey()] = pair
+		hashedPairs[hashKey.Hash()] = pair
 	}
 
 	return &object.Hash{Pairs: hashedPairs}, nil
diff --git a/internal/vm/vm_test.go b/internal/vm/vm_test.go
index b0b32b5..b4af1e8 100644
--- a/internal/vm/vm_test.go
+++ b/internal/vm/vm_test.go
@@ -379,15 +379,15 @@ func TestHashLiterals(t *testing.T) {
 		{
 			"{1: 2, 2: 3}",
 			map[object.HashKey]int64{
-				(object.Integer{Value: 1}).HashKey(): 2,
-				(object.Integer{Value: 2}).HashKey(): 3,
+				(object.Integer{Value: 1}).Hash(): 2,
+				(object.Integer{Value: 2}).Hash(): 3,
 			},
 		},
 		{
 			"{1 + 1: 2 * 2, 3 + 3: 4 * 4}",
 			map[object.HashKey]int64{
-				(object.Integer{Value: 2}).HashKey(): 4,
-				(object.Integer{Value: 6}).HashKey(): 16,
+				(object.Integer{Value: 2}).Hash(): 4,
+				(object.Integer{Value: 6}).Hash(): 16,
 			},
 		},
 	}
@@ -400,14 +400,14 @@ func TestHashMerging(t *testing.T) {
 		{
 			`{} + {"a": 1}`,
 			map[object.HashKey]int64{
-				(object.String{Value: "a"}).HashKey(): 1,
+				(object.String{Value: "a"}).Hash(): 1,
 			},
 		},
 		{
 			`{"a": 1} + {"b": 2}`,
 			map[object.HashKey]int64{
-				(object.String{Value: "a"}).HashKey(): 1,
-				(object.String{Value: "b"}).HashKey(): 2,
+				(object.String{Value: "a"}).Hash(): 1,
+				(object.String{Value: "b"}).Hash(): 2,
 			},
 		},
 	}
diff --git a/profile.go b/profile.go
index d184810..f67510d 100644
--- a/profile.go
+++ b/profile.go
@@ -6,15 +6,14 @@ import (
 	"flag"
 	"fmt"
 	"log"
+	"monkey/internal/compiler"
+	"monkey/internal/object"
+	"monkey/internal/parser"
+	"monkey/internal/vm"
 	"os"
 	"runtime"
 	"runtime/pprof"
 	"strings"
-
-	"git.mills.io/prologic/monkey-lang/internal/compiler"
-	"git.mills.io/prologic/monkey-lang/internal/object"
-	"git.mills.io/prologic/monkey-lang/internal/parser"
-	"git.mills.io/prologic/monkey-lang/internal/vm"
 )
 
 const defaultCode = `