Add new functions to the iterable package:

- Filter
- Find
- Partition

R=rsc
APPROVED=rsc
DELTA=117  (92 added, 17 deleted, 8 changed)
OCL=27135
CL=27240

2 files changed, 99 insertions, 24 deletions

diff --git a/src/lib/container/iterable.go b/src/lib/container/iterable.go
index 7963d14b5..a4a0d4c0f 100644
--- a/src/lib/container/iterable.go
+++ b/src/lib/container/iterable.go
@@ -10,15 +10,17 @@ package iterable
 
 import "vector"
 
-
 type Iterable interface {
 	// Iter should return a fresh channel each time it is called.
 	Iter() <-chan interface {}
 }
 
+func not(f func(interface {}) bool) (func(interface {}) bool) {
+  return func(e interface {}) bool { return !f(e) }
+}
 
 // All tests whether f is true for every element of iter.
-func All(iter Iterable, f func(e interface {}) bool) bool {
+func All(iter Iterable, f func(interface {}) bool) bool {
 	for e := range iter.Iter() {
 		if !f(e) {
 			return false
@@ -27,13 +29,11 @@ func All(iter Iterable, f func(e interface {}) bool) bool {
 	return true
 }
 
-
 // Any tests whether f is true for at least one element of iter.
-func Any(iter Iterable, f func(e interface {}) bool) bool {
-	return !All(iter, func(e interface {}) bool { return !f(e) });
+func Any(iter Iterable, f func(interface {}) bool) bool {
+	return !All(iter, not(f))
 }
 
-
 // Data returns a slice containing the elements of iter.
 func Data(iter Iterable) []interface {} {
 	vec := vector.New(0);
@@ -43,6 +43,41 @@ func Data(iter Iterable) []interface {} {
 	return vec.Data()
 }
 
+// filteredIterable is a struct that implements Iterable with each element
+// passed through a filter.
+type filteredIterable struct {
+	it Iterable;
+	f func(interface {}) bool;
+}
+
+func (f *filteredIterable) iterate(out chan<- interface {}) {
+	for e := range f.it.Iter() {
+		if f.f(e) {
+			out <- e
+		}
+	}
+	close(out)
+}
+
+func (f *filteredIterable) Iter() <-chan interface {} {
+	ch := make(chan interface {});
+	go f.iterate(ch);
+	return ch;
+}
+
+// Filter returns an Iterable that returns the elements of iter that satisfy f.
+func Filter(iter Iterable, f func(interface {}) bool) Iterable {
+	return &filteredIterable{ iter, f }
+}
+
+// Find returns the first element of iter that satisfies f.
+// Returns nil if no such element is found.
+func Find(iter Iterable, f func(interface {}) bool) interface {} {
+	for e := range Filter(iter, f).Iter() {
+		return e
+	}
+	return nil
+}
 
 // mappedIterable is a helper struct that implements Iterable, returned by Map.
 type mappedIterable struct {
@@ -50,31 +85,30 @@ type mappedIterable struct {
 	f func(interface {}) interface {};
 }
 
-
-func (m mappedIterable) iterate(out chan<- interface {}) {
+func (m *mappedIterable) iterate(out chan<- interface {}) {
 	for e := range m.it.Iter() {
 		out <- m.f(e)
 	}
 	close(out)
 }
 
-
-func (m mappedIterable) Iter() <-chan interface {} {
+func (m *mappedIterable) Iter() <-chan interface {} {
 	ch := make(chan interface {});
 	go m.iterate(ch);
 	return ch;
 }
 
-
 // Map returns an Iterable that returns the result of applying f to each
 // element of iter.
-func Map(iter Iterable, f func(e interface {}) interface {}) Iterable {
-	return mappedIterable{ iter, f }
+func Map(iter Iterable, f func(interface {}) interface {}) Iterable {
+	return &mappedIterable{ iter, f }
 }
 
+// Partition(iter, f) returns Filter(iter, f) and Filter(iter, !f).
+func Partition(iter Iterable, f func(interface {}) bool) (Iterable, Iterable)  {
+  return Filter(iter, f), Filter(iter, not(f))
+}
 
 // TODO:
-// - Find, Filter
 // - Inject
-// - Partition
 // - Zip
diff --git a/src/lib/container/iterable_test.go b/src/lib/container/iterable_test.go
index 9c7d29110..702ebe861 100644
--- a/src/lib/container/iterable_test.go
+++ b/src/lib/container/iterable_test.go
@@ -43,6 +43,17 @@ func addOne(n interface {}) interface {} {
 	return n.(int) + 1
 }
 
+// A stream of the natural numbers: 0, 1, 2, 3, ...
+type integerStream struct {}
+func (i integerStream) Iter() <-chan interface {} {
+  ch := make(chan interface {});
+  go func() {
+    for i := 0; ; i++ {
+      ch <- i
+    }
+  }();
+  return ch
+}
 
 func TestAll(t *testing.T) {
 	if !All(oneToFive, isPositive) {
@@ -53,7 +64,6 @@ func TestAll(t *testing.T) {
 	}
 }
 
-
 func TestAny(t *testing.T) {
 	if Any(oneToFive, isNegative) {
 		t.Error("Any(oneToFive, isNegative) == true")
@@ -63,16 +73,47 @@ func TestAny(t *testing.T) {
 	}
 }
 
-
-func TestMap(t *testing.T) {
-	res := Data(Map(Map(oneToFive, doubler), addOne));
-	if len(res) != len(oneToFive) {
-		t.Fatal("len(res) = %v, want %v", len(res), len(oneToFive))
+func assertArraysAreEqual(t *testing.T, res []interface {}, expected []int) {
+	if len(res) != len(expected) {
+		t.Errorf("len(res) = %v, want %v", len(res), len(expected));
+		goto missing
 	}
-	expected := []int{ 3, 5, 7, 9, 11 };
 	for i := range res {
-		if res[i].(int) != expected[i] {
-			t.Errorf("res[%v] = %v, want %v", i, res[i], expected[i])
+		if v := res[i].(int); v != expected[i] {
+			t.Errorf("res[%v] = %v, want %v", i, v, expected[i]);
+			goto missing
 		}
 	}
+	return;
+missing:
+	t.Errorf("res = %v\nwant  %v", res, expected);
+}
+
+func TestFilter(t *testing.T) {
+	ints := integerStream{};
+	moreInts := Filter(ints, isAbove3).Iter();
+	res := make([]interface {}, 3);
+	for i := 0; i < 3; i++ {
+		res[i] = <-moreInts;
+	}
+	assertArraysAreEqual(t, res, []int{ 4, 5, 6 })
+}
+
+func TestFind(t *testing.T) {
+	ints := integerStream{};
+	first := Find(ints, isAbove3);
+	if first.(int) != 4 {
+		t.Errorf("Find(ints, isAbove3) = %v, want 4", first)
+	}
+}
+
+func TestMap(t *testing.T) {
+	res := Data(Map(Map(oneToFive, doubler), addOne));
+	assertArraysAreEqual(t, res, []int{ 3, 5, 7, 9, 11 })
+}
+
+func TestPartition(t *testing.T) {
+	ti, fi := Partition(oneToFive, isEven);
+	assertArraysAreEqual(t, Data(ti), []int{ 2, 4 });
+	assertArraysAreEqual(t, Data(fi), []int{ 1, 3, 5 })
 }