Add Compact iterator

Author: BooleanCat

README.md

@@ -431,6 +431,19 @@ for number := range itx.FromChannel(items).Exclude(filter.IsZero) {
 > In order to prevent a deadlock, the channel must be closed before attemping to stop the iterator
 > when it's used in a pull style. See [iter.Pull](https://pkg.go.dev/iter#Pull).
 
+### Compact
+
+Compact yields all values from a delegate iterator that are not zero values. It is functionally
+equivalent to `it.Filter(delegate, filter.IsZero)`.
+
+```go
+words := it.Compact(slices.Values([]string{"foo", "", "bar", "", ""}))
+```
+
+<!-- prettier-ignore -->
+> [!NOTE]
+> The `itx` package does not contain `Compact` due to limitations with Go's type system.
+
 ### Cycle
 
 Cycle yields all values from an iterator before returning to the beginning and yielding all values

it/compact.go

@@ -0,0 +1,19 @@
+package it
+
+import "iter"
+
+// Compact yields all values from a delegate iterator that are not zero values.
+func Compact[V comparable](delegate func(func(V) bool)) iter.Seq[V] {
+	return func(yield func(V) bool) {
+		for value := range delegate {
+			var zero V
+			if zero == value {
+				continue
+			}
+
+			if !yield(value) {
+				return
+			}
+		}
+	}
+}

it/compact_test.go

@@ -0,0 +1,47 @@
+package it_test
+
+import (
+	"fmt"
+	"slices"
+	"testing"
+
+	"github.com/BooleanCat/go-functional/v2/internal/assert"
+	"github.com/BooleanCat/go-functional/v2/it"
+)
+
+func ExampleCompact() {
+	words := slices.Values([]string{"", "foo", "", "", "bar", ""})
+	fmt.Println(slices.Collect(it.Compact(words)))
+	// Output: [foo bar]
+}
+
+func TestCompactEmpty(t *testing.T) {
+	t.Parallel()
+
+	words := slices.Collect(it.Compact(it.Exhausted[string]()))
+	assert.Empty[string](t, words)
+}
+
+func TestCompactOnlyEmpty(t *testing.T) {
+	t.Parallel()
+
+	words := slices.Values([]string{"", "", "", ""})
+	assert.Empty[string](t, slices.Collect(it.Compact(words)))
+}
+
+func TestCompactOnlyNotEmpty(t *testing.T) {
+	t.Parallel()
+
+	words := slices.Values([]string{"foo", "bar"})
+	assert.SliceEqual(t, slices.Collect(it.Compact(words)), []string{"foo", "bar"})
+}
+
+func TestCompactYieldFalse(t *testing.T) {
+	t.Parallel()
+
+	words := it.Compact(slices.Values([]string{"foo", "bar"}))
+
+	words(func(string) bool {
+		return false
+	})
+}