decode3

3 files changed, 62 insertions, 1 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index a4e13de..ee8c6f3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -17,7 +17,7 @@
 - The decoder functions of the `dynamic` module now return multiple errors.
 - The `dynamic.any`, `dynamic.element` and `dynamic.tuple*` functions are now
   partially applied.
-- The `dynamic` module gains the `decode2` function.
+- The `dynamic` module gains the `decode2`, `decode3` functions.
 - The `int` module gains the `digits` and `undigits` functions.
 
 ## v0.18.1 - 2021-12-19
diff --git a/src/gleam/dynamic.gleam b/src/gleam/dynamic.gleam
index 4571b20..9aea340 100644
--- a/src/gleam/dynamic.gleam
+++ b/src/gleam/dynamic.gleam
@@ -910,6 +910,40 @@ pub fn decode2(
   }
 }
 
+/// Decode 3 values from a `Dynamic` value.
+///
+/// ## Examples
+///
+/// ```gleam
+/// > from(#(1, 2.0, "3"))
+/// > |> decode2(MyRecord, element(0, int), element(1, float), element(2, string))
+/// Ok(MyRecord(1, 2.0, "3"))
+/// ```
+///
+/// ```gleam
+/// > from(#("", "", ""))
+/// > |> decode2(MyRecord, element(0, int), element(1, float), element(2, string))
+/// Error([
+///   DecodeError(expected: "Int", found: "String", path: ["0"]),
+///   DecodeError(expected: "Float", found: "String", path: ["1"]),
+/// ])
+/// ```
+///
+pub fn decode3(
+  constructor: fn(t1, t2, t3) -> t,
+  decode1: Decoder(t1),
+  decode2: Decoder(t2),
+  decode3: Decoder(t3),
+) -> Decoder(t) {
+  fn(value) {
+    case decode1(value), decode2(value), decode3(value) {
+      Ok(a), Ok(b), Ok(c) -> Ok(constructor(a, b, c))
+      a, b, c ->
+        Error(list.flatten([all_errors(a), all_errors(b), all_errors(c)]))
+    }
+  }
+}
+
 fn all_errors(result: Result(a, List(DecodeError))) -> List(DecodeError) {
   case result {
     Ok(_) -> []
diff --git a/test/gleam/dynamic_test.gleam b/test/gleam/dynamic_test.gleam
index 1bfc255..c597b4e 100644
--- a/test/gleam/dynamic_test.gleam
+++ b/test/gleam/dynamic_test.gleam
@@ -811,3 +811,30 @@ pub fn decode2_test() {
     DecodeError(expected: "Float", found: "Int", path: ["1"]),
   ]))
 }
+
+type Three(a, b, c) {
+  Three(a, b, c)
+}
+
+pub fn decode3_test() {
+  let decoder =
+    dynamic.decode3(
+      Three,
+      dynamic.element(0, dynamic.int),
+      dynamic.element(1, dynamic.float),
+      dynamic.element(2, dynamic.int),
+    )
+
+  #(1, 2.0, 3)
+  |> dynamic.from
+  |> decoder
+  |> should.equal(Ok(Three(1, 2.0, 3)))
+
+  #(1.3, 2, 3)
+  |> dynamic.from
+  |> decoder
+  |> should.equal(Error([
+    DecodeError(expected: "Int", found: "Float", path: ["0"]),
+    DecodeError(expected: "Float", found: "Int", path: ["1"]),
+  ]))
+}