Add iter.FromSeq{,2}{,Context} (#13)

* Checkpoint.

* Add test coverage.

* Add coverage.

* Add coverage.

iter/iter.go

@@ -5,6 +5,8 @@
 // (a preview of which is available in Go 1.22 when building with GOEXPERIMENT=rangefunc).
 package iter
 
+import "context"
+
 // Of is the interface implemented by iterators.
 // It is called "Of" so that when qualified with this package name
 // and instantiated with a member type,
@@ -98,3 +100,55 @@ func AllPairs[T, U any](inp Of[Pair[T, U]]) Seq2[T, U] {
 		}
 	}
 }
+
+// FromSeq converts a Go 1.23 iterator into an Of[T].
+func FromSeq[T any](seq Seq[T]) Of[T] {
+	return Go(func(ch chan<- T) error {
+		seq(func(v T) bool {
+			ch <- v
+			return true
+		})
+		return nil
+	})
+}
+
+// FromSeqContext converts a Go 1.23 iterator into an Of[T].
+func FromSeqContext[T any](ctx context.Context, seq Seq[T]) Of[T] {
+	return Go(func(ch chan<- T) error {
+		seq(func(v T) bool {
+			select {
+			case <-ctx.Done():
+				return false
+			case ch <- v:
+				return true
+			}
+		})
+		return ctx.Err()
+	})
+}
+
+// FromSeq2 converts a Go 1.23 pair iterator into an Of[Pair[T, U]].
+func FromSeq2[T, U any](seq Seq2[T, U]) Of[Pair[T, U]] {
+	return Go(func(ch chan<- Pair[T, U]) error {
+		seq(func(t T, u U) bool {
+			ch <- Pair[T, U]{X: t, Y: u}
+			return true
+		})
+		return nil
+	})
+}
+
+// FromSeq2Context converts a Go 1.23 pair iterator into an Of[Pair[T, U]].
+func FromSeq2Context[T, U any](ctx context.Context, seq Seq2[T, U]) Of[Pair[T, U]] {
+	return Go(func(ch chan<- Pair[T, U]) error {
+		seq(func(t T, u U) bool {
+			select {
+			case <-ctx.Done():
+				return false
+			case ch <- Pair[T, U]{X: t, Y: u}:
+				return true
+			}
+		})
+		return ctx.Err()
+	})
+}

iter/iter_test.go

@@ -1,6 +1,8 @@
 package iter
 
 import (
+	"context"
+	"errors"
 	"reflect"
 	"testing"
 )
@@ -63,3 +65,109 @@ func testSeq2[T, U any](t *testing.T, seq Seq2[T, U], wantT []T, wantU []U) {
 		t.Errorf("got %v, want %v", gotU, wantU)
 	}
 }
+
+func TestFromSeq(t *testing.T) {
+	seq := func(yield func(int) bool) {
+		for i := 0; i < 5; i++ {
+			if !yield(i) {
+				break
+			}
+		}
+	}
+	it := FromSeq(seq)
+	got, err := ToSlice(it)
+	if err != nil {
+		t.Fatal(err)
+	}
+	want := []int{0, 1, 2, 3, 4}
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("got %v, want %v", got, want)
+	}
+}
+
+func TestFromSeq2(t *testing.T) {
+	names := []string{"Alice", "Bob", "Carol"}
+	seq2 := func(yield func(int, string) bool) {
+		for i, name := range names {
+			if !yield(i, name) {
+				break
+			}
+		}
+	}
+	it := FromSeq2(seq2)
+	got, err := ToSlice(it)
+	if err != nil {
+		t.Fatal(err)
+	}
+	want := []Pair[int, string]{{0, "Alice"}, {1, "Bob"}, {2, "Carol"}}
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("got %v, want %v", got, want)
+	}
+}
+
+func TestFromSeqContext(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	seq := func(yield func(int) bool) {
+		for i := 0; i < 5; i++ {
+			if !yield(i) {
+				break
+			}
+		}
+	}
+
+	it := FromSeqContext(ctx, seq)
+
+	if !it.Next() {
+		t.Fatal("it.Next() returned false, want true")
+	}
+	val0 := it.Val()
+	if val0 != 0 {
+		t.Errorf("got %v, want 0", val0)
+	}
+
+	cancel()
+
+	got, err := ToSlice(it)
+	if !errors.Is(err, context.Canceled) {
+		t.Errorf("got %v, want %v", err, context.Canceled)
+	}
+	if len(got) > 0 {
+		t.Errorf("got %v, want []", got)
+	}
+}
+
+func TestFromSeq2Context(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	names := []string{"Alice", "Bob", "Carol"}
+	seq2 := func(yield func(int, string) bool) {
+		for i, name := range names {
+			if !yield(i, name) {
+				break
+			}
+		}
+	}
+
+	it := FromSeq2Context(ctx, seq2)
+
+	if !it.Next() {
+		t.Fatal("it.Next() returned false, want true")
+	}
+	val0 := it.Val()
+	if val0.X != 0 || val0.Y != "Alice" {
+		t.Errorf("got %v, want {0, Alice}", val0)
+	}
+
+	cancel()
+
+	got, err := ToSlice(it)
+	if !errors.Is(err, context.Canceled) {
+		t.Errorf("got %v, want %v", err, context.Canceled)
+	}
+	if len(got) > 0 {
+		t.Errorf("got %v, want []", got)
+	}
+}