dynamic.opaque_list

2 files changed, 41 insertions, 4 deletions

diff --git a/src/gleam/dynamic.gleam b/src/gleam/dynamic.gleam
index 89826ec..3778a47 100644
--- a/src/gleam/dynamic.gleam
+++ b/src/gleam/dynamic.gleam
@@ -113,14 +113,29 @@ pub external fn bool(from: Dynamic) -> Result(Bool, String) =
 pub external fn thunk(from: Dynamic) -> Result(fn() -> Dynamic, String) =
   "gleam_stdlib" "decode_thunk"
 
-external fn list_dynamic(from: Dynamic) -> Result(List(Dynamic), String) =
-  "gleam_stdlib" "decode_list"
-
 /// Check to see whether a Dynamic value is a list, and return the list if it
 /// is.
 ///
 /// ## Examples
 ///
+///    > opaque_list(from(["a", "b", "c"]))
+///    Ok([from("a"), from("b"), from("c")])
+///
+///    > opaque_list(1)
+///    Error("Expected an Int, got a binary")
+///
+pub external fn opaque_list(from: Dynamic) -> Result(List(Dynamic), String) =
+  "gleam_stdlib" "decode_list"
+
+/// Check to see whether a Dynamic value is a list of a particular type, and
+/// return the list if it is.
+///
+/// The second argument is a decoder function used to decode the elements of
+/// the list. The list is only decoded if all elements in the list can be
+/// successfully decoded using this function.
+///
+/// ## Examples
+///
 ///    > list(from(["a", "b", "c"]), string)
 ///    Ok(["a", "b", "c"])
 ///
@@ -135,7 +150,7 @@ pub fn list(
   containing decoder_type: fn(Dynamic) -> Result(inner, String),
 ) -> Result(List(inner), String) {
   dynamic
-  |> list_dynamic
+  |> opaque_list
   |> result.then(list_mod.traverse(_, decoder_type))
 }
 
diff --git a/test/gleam/dynamic_test.gleam b/test/gleam/dynamic_test.gleam
index 5b5a88c..410ae0e 100644
--- a/test/gleam/dynamic_test.gleam
+++ b/test/gleam/dynamic_test.gleam
@@ -316,3 +316,25 @@ pub fn map_test() {
   |> dynamic.map
   |> should.equal(Error("Expected a map, got an int"))
 }
+
+pub fn opaque_list_test() {
+  []
+  |> dynamic.from
+  |> dynamic.opaque_list
+  |> should.equal(Ok([]))
+
+  [1, 2]
+  |> dynamic.from
+  |> dynamic.opaque_list
+  |> should.equal(Ok([dynamic.from(1), dynamic.from(2)]))
+
+  [dynamic.from(1), dynamic.from(2.0)]
+  |> dynamic.from
+  |> dynamic.opaque_list
+  |> should.equal(Ok([dynamic.from(1), dynamic.from(2.0)]))
+
+  1
+  |> dynamic.from
+  |> dynamic.opaque_list
+  |> should.equal(Error("Expected a list, got an int"))
+}