Implement list Map

Author: tylertreat-wf

list/persistent.go

@@ -69,6 +69,10 @@ type PersistentList interface {
 	// FindIndex applies the predicate function to the list and returns the
 	// index of the first item which matches or -1 if there is no match.
 	FindIndex(func(interface{}) bool) int
+
+	// Map applies the function to each entry in the list and returns the
+	// resulting slice.
+	Map(func(interface{}) interface{}) []interface{}
 }
 
 type emptyList struct{}
@@ -133,6 +137,12 @@ func (e *emptyList) FindIndex(func(interface{}) bool) int {
 	return -1
 }
 
+// Map applies the function to each entry in the list and returns the resulting
+// slice.
+func (e *emptyList) Map(func(interface{}) interface{}) []interface{} {
+	return nil
+}
+
 type list struct {
 	head interface{}
 	tail PersistentList
@@ -237,3 +247,9 @@ func (l *list) FindIndex(pred func(interface{}) bool) int {
 		idx += 1
 	}
 }
+
+// Map applies the function to each entry in the list and returns the resulting
+// slice.
+func (l *list) Map(f func(interface{}) interface{}) []interface{} {
+	return append(l.tail.Map(f), f(l.head))
+}

list/persistent_test.go

@@ -276,3 +276,14 @@ func TestLength(t *testing.T) {
 	l = l.Add("bar").Add("baz")
 	assert.Equal(uint(3), l.Length())
 }
+
+func TestMap(t *testing.T) {
+	assert := assert.New(t)
+	f := func(x interface{}) interface{} {
+		return x.(int) * x.(int)
+	}
+	assert.Nil(Empty.Map(f))
+
+	l := Empty.Add(1).Add(2).Add(3).Add(4)
+	assert.Equal([]interface{}{1, 4, 9, 16}, l.Map(f))
+}