bring back empty() vs new(val)

list/list.go

@@ -5,11 +5,13 @@ import (
 	"strings"
 )
 
+
 type IList interface {
 	Conj(data any) IList
 	First() any
 	Rest() IList
 	String() string
+	IsEmpty() bool
 }
 
 type EmptyList struct{}
@@ -19,22 +21,21 @@ type List struct {
 	next  IList
 }
 
-func New() IList {
+func Empty() IList {
 	return new(EmptyList)
 }
 
-func single(val any) *List {
+var emptyList = Empty()
+
+func New(val any) *List {
 	this := new(List)
 	this.Value = val
-	this.next = nil
+	this.next = emptyList
 	return this
 }
 
 func (this *List) Conj(val any) IList {
-	if this == nil {
+	new_head := New(val)
-		return single(val)
-	}
-	new_head := single(val)
 	new_head.next = this
 	return new_head
 
@@ -45,31 +46,29 @@ func (this *EmptyList) Conj(val any) IList {
 }
 
 func Conj(this IList, val any) IList {
-	var l IList
 	if this == nil {
-		l = single(val)
+		return New(val)
 	} else {
-		l = this
+		return this.Conj(val)
 	}
-	return l.Conj(val)
 }
 
 func Rest(this IList) IList {
 	if this == nil {
-		return nil
+		return emptyList
 	}
 	return this.Rest()
 }
 
 func (this *List) Rest() IList {
 	if this == nil {
-		return nil
+		return emptyList
 	}
 	return this.next
 }
 
 func (this *EmptyList) Rest() IList {
-	return nil
+	return emptyList
 }
 
 func First(this *List) any {
@@ -84,15 +83,15 @@ func (this *List) First() any {
 }
 
 func (this *EmptyList) First() any {
-	return First(nil)
+	return nil
 }
 
 func IsEmpty(this IList) bool {
-	return this == nil
+	return this == nil || this.IsEmpty()
 }
 
 func (this *List) IsEmpty() bool {
-	return this == nil
+	return false
 }
 
 func (this *EmptyList) IsEmpty() bool {
@@ -100,21 +99,17 @@ func (this *EmptyList) IsEmpty() bool {
 }
 
 func String(this *List) string {
-	if this == nil {
+	if IsEmpty(this) {
 		return "()"
 	}
+
 	var sb strings.Builder
 	sb.WriteRune('(')
 	// Iterate and print elements
 	var e IList
-	for e = this; e != nil; e = Rest(e) {
+	for e = this; !IsEmpty(e); e = Rest(e) {
-		switch v := e.(type) {
+		sb.WriteString(fmt.Sprint(e.First()))
-		case *List:
+		sb.WriteRune(' ')
-			sb.WriteString(fmt.Sprint(v.Value))
-			sb.WriteRune(' ')
-		case *EmptyList:
-			break
-		}
 	}
 	return sb.String()[:sb.Len()-1] + ")"
 }
@@ -124,5 +119,5 @@ func (this *List) String() string {
 }
 
 func (this *EmptyList) String() string {
-	return String(nil)
+	return "()"
 }

list/list_test.go

@@ -5,25 +5,30 @@ import (
 	"testing"
 )
 
+func TestReadString(t *testing.T) {
+	assert.Equal(t, "()", Empty().String(), "should insert at head")
+}
+
 func TestReadConj(t *testing.T) {
-	l := New().Conj(5).Conj(6).Conj(7)
+	var l IList
-	assert.Equal(t, "(7 6 5)", l.String(), "should insert at head")
+	assert.Equal(t, "()", Empty().String(), "should insert at head")
-	l = Conj(New(), 4)
+	l = New(5)
-	assert.Equal(t, "(4 5)", l.String(), "should insert at head")
+	assert.Equal(t, "(5)", l.String(), "should insert at head")
+	l = Empty().Conj(4)
+	assert.Equal(t, "(4)", l.String(), "should insert at head")
 }
 
 func TestReadFirst(t *testing.T) {
-	l := New().Conj(5).Conj(6).Conj(7)
+	l := Empty().Conj(5).Conj(6).Conj(7)
 	assert.Equal(t, 7, l.First(), "should return first element")
-	assert.Equal(t, nil, New().First(), "should return nil")
+	assert.Equal(t, nil, Empty().First(), "should return nil")
 }
 
 func TestReadRest(t *testing.T) {
-	l := New().Conj(5).Conj(6).Conj(7)
+	l := Empty().Conj(5).Conj(6).Conj(7)
 	assert.Equal(t, "(6 5)", l.Rest().String(), "should return rest sublist")
 	assert.Equal(t, "(5)", l.Rest().Rest().String(), "should return rest sublist")
 	assert.Equal(t, "()", l.Rest().Rest().Rest().String(), "should return rest sublist")
-	var nilPtr *List = nil
+	assert.Equal(t, Empty(), Empty().Rest(), "should return rest sublist")
-	assert.Equal(t, nilPtr, New().Rest(), "should return rest sublist")
+	assert.Equal(t, Empty(), Rest(Empty().Rest()), "should return rest sublist")
-	assert.Equal(t, nilPtr, Rest(New().Rest()), "should return rest sublist")
 }

read/read_test.go

@@ -43,7 +43,7 @@ func TestReadListElem(t *testing.T) {
 func TestReadList(t *testing.T) {
 	input := "(1 2 3)"
 	l, err, pos := readList(input, 0, "user")
-	assert.Equal(t, list.New().Conj(3).Conj(2).Conj(1), l, "should read list")
+	assert.Equal(t, list.Empty().Conj(3).Conj(2).Conj(1), l, "should read list")
 	assert.Equal(t, nil, err, "should read without error")
 	assert.Equal(t, len(input), pos, "should read the whole string")
 }

vector/vector.go

@@ -52,7 +52,7 @@ func (this *Vector) String() string {
 }
 
 func ToList(this *Vector) list.IList {
-	l := list.New()
+	l := list.Empty()
 	for i := len(this._slice) - 1; i >= 0; i-- {
 		l = list.Conj(l, this._slice[i])
 	}