add Traverse to seq

seq/seq.go

@@ -286,3 +286,27 @@ func DropWhile(pred func(types.Elem) bool, s Seq) Seq {
 	}
 	return s
 }
+
+// Runs pred on each element in the sequence, descending recursively if it
+// encounters another Seq (without calling pred on that Seq). This amounts to a
+// depth-first traverse. If pred ever returns false the traverse will stop.
+// Returns false if the Traverse was stopped by pred, true otherwise.
+func Traverse(pred func(types.Elem) bool, s Seq) bool {
+	var el types.Elem
+	var ok bool
+	for {
+		el, s, ok = s.FirstRest()
+		if !ok {
+			return true
+		}
+		var predRet bool
+		if inners, ok := el.(Seq); ok {
+			predRet = Traverse(pred, inners)
+		} else {
+			predRet = pred(el)
+		}
+		if !predRet {
+			return false
+		}
+	}
+}

seq/seq_test.go

@@ -379,3 +379,49 @@ func TestDropWhile(t *T) {
 	assertEmpty(l, t)
 	assertEmpty(nl, t)
 }
+
+// Test Traversing a Seq until a given condition
+func TestTraverse(t *T) {
+	var acc int
+	pred := func(el types.Elem) bool {
+		acc += el.(types.GoType).V.(int)
+		return true
+	}
+
+	l := NewList()
+	acc = 0
+	Traverse(pred, l)
+	assertValue(acc, 0, t)
+
+	l2 := NewList(elemSliceV(0, 1, 2, 3)...)
+	acc = 0
+	Traverse(pred, l2)
+	assertValue(acc, 6, t)
+
+	l3 := NewList(
+		types.GoType{1},
+		types.GoType{2},
+		NewList(elemSliceV(4, 5, 6)...),
+		types.GoType{3},
+	)
+	acc = 0
+	Traverse(pred, l3)
+	assertValue(acc, 21, t)
+
+	pred = func(el types.Elem) bool {
+		i := el.(types.GoType).V.(int)
+		if i > 4 {
+			return false
+		}
+		acc += i
+		return true
+	}
+
+	acc = 0
+	Traverse(pred, l2)
+	assertValue(acc, 6, t)
+
+	acc = 0
+	Traverse(pred, l3)
+	assertValue(acc, 7, t)
+}