fold test

2 files changed, 30 insertions, 5 deletions

diff --git a/src/gleam/iterator.gleam b/src/gleam/iterator.gleam
index 6634f23..b51987d 100644
--- a/src/gleam/iterator.gleam
+++ b/src/gleam/iterator.gleam
@@ -48,7 +48,9 @@ fn do_unfold(initial, f) {
 // TODO: test
 // TODO: document
 pub fn unfold(from initial: acc, with f: fn(acc) -> Step(element, acc)) -> Iterator(element) {
-  opaque(do_unfold(initial, f))
+  initial
+  |> do_unfold(_, f)
+  |> opaque
 }
 
 // TODO: test
@@ -82,10 +84,11 @@ fn do_fold(iterator, initial, f) {
   }
 }
 
-// TODO: test
 // TODO: document
 pub fn fold(over iterator: Iterator(e), from initial: acc, with f: fn(e, acc) -> acc) -> acc {
-  do_fold(unopaque(iterator), initial, f)
+  iterator
+  |> unopaque
+  |> do_fold(_, initial, f)
 }
 
 // TODO: test
@@ -134,7 +137,10 @@ fn do_map(iterator, f) {
 // TODO: test
 // TODO: document
 pub fn map(over iterator: Iterator(a), with f: fn(a) -> b) -> Iterator(b) {
-  opaque(do_map(unopaque(iterator), f))
+  iterator
+  |> unopaque
+  |> do_map(_, f)
+  |> opaque
 }
 
 fn do_filter(iterator, predicate) {
@@ -152,5 +158,8 @@ fn do_filter(iterator, predicate) {
 // TODO: test
 // TODO: document
 pub fn filter(iterator: Iterator(a), for predicate: fn(a) -> Bool) -> Iterator(a) {
-  opaque(do_filter(unopaque(iterator), predicate))
+  iterator
+  |> unopaque
+  |> do_filter(_, predicate)
+  |> opaque
 }
diff --git a/test/gleam/iterator_test.gleam b/test/gleam/iterator_test.gleam
index 2d9ee3f..46ac65a 100644
--- a/test/gleam/iterator_test.gleam
+++ b/test/gleam/iterator_test.gleam
@@ -39,3 +39,19 @@ pub fn take_test() {
   test(2, [0, 1, 2, 3, 4])
   test(22, [0, 1, 2, 3, 4])
 }
+
+// a |> from_list |> fold(_, a, f) == a |> list.fold(_, a, f)
+pub fn fold_test() {
+  let test = fn(subject, acc, f) {
+    subject
+    |> iterator.from_list
+    |> iterator.fold(_, acc, f)
+    |> expect.equal(_, list.fold(subject, acc, f))
+  }
+
+  let f = fn(e, acc) { [e | acc] }
+  test([], [], f)
+  test([1], [], f)
+  test([1, 2, 3], [], f)
+  test([1, 2, 3, 4, 5, 6, 7, 8], [], f)
+}